/* * pcap-linux.c: Packet capture interface to the Linux kernel * * Copyright (c) 2000 Torsten Landschoff * Sebastian Krahmer * * License: BSD * * Redistribution and use in source and binary forms, with or without * modification, are permitted provided that the following conditions * are met: * * 1. Redistributions of source code must retain the above copyright * notice, this list of conditions and the following disclaimer. * 2. Redistributions in binary form must reproduce the above copyright * notice, this list of conditions and the following disclaimer in * the documentation and/or other materials provided with the * distribution. * 3. The names of the authors may not be used to endorse or promote * products derived from this software without specific prior * written permission. * * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR * IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. */ #ifndef lint static const char rcsid[] _U_ = "@(#) $Header: /tcpdump/master/libpcap/pcap-linux.c,v 1.98.2.4 2003/11/21 10:20:46 guy Exp $ (LBL)"; #endif /* * Known problems with 2.0[.x] kernels: * * - The loopback device gives every packet twice; on 2.2[.x] kernels, * if we use PF_PACKET, we can filter out the transmitted version * of the packet by using data in the "sockaddr_ll" returned by * "recvfrom()", but, on 2.0[.x] kernels, we have to use * PF_INET/SOCK_PACKET, which means "recvfrom()" supplies a * "sockaddr_pkt" which doesn't give us enough information to let * us do that. * * - We have to set the interface's IFF_PROMISC flag ourselves, if * we're to run in promiscuous mode, which means we have to turn * it off ourselves when we're done; the kernel doesn't keep track * of how many sockets are listening promiscuously, which means * it won't get turned off automatically when no sockets are * listening promiscuously. We catch "pcap_close()" and, for * interfaces we put into promiscuous mode, take them out of * promiscuous mode - which isn't necessarily the right thing to * do, if another socket also requested promiscuous mode between * the time when we opened the socket and the time when we close * the socket. * * - MSG_TRUNC isn't supported, so you can't specify that "recvfrom()" * return the amount of data that you could have read, rather than * the amount that was returned, so we can't just allocate a buffer * whose size is the snapshot length and pass the snapshot length * as the byte count, and also pass MSG_TRUNC, so that the return * value tells us how long the packet was on the wire. * * This means that, if we want to get the actual size of the packet, * so we can return it in the "len" field of the packet header, * we have to read the entire packet, not just the part that fits * within the snapshot length, and thus waste CPU time copying data * from the kernel that our caller won't see. * * We have to get the actual size, and supply it in "len", because * otherwise, the IP dissector in tcpdump, for example, will complain * about "truncated-ip", as the packet will appear to have been * shorter, on the wire, than the IP header said it should have been. */ #ifdef HAVE_CONFIG_H #include "config.h" #endif #include "pcap-int.h" #include "sll.h" #ifdef HAVE_DAG_API #include "pcap-dag.h" #endif /* HAVE_DAG_API */ #include #include #include #include #include #include #include #include #include #include #include #include /* * If PF_PACKET is defined, we can use {SOCK_RAW,SOCK_DGRAM}/PF_PACKET * sockets rather than SOCK_PACKET sockets. * * To use them, we include rather than * ; we do so because * * some Linux distributions (e.g., Slackware 4.0) have 2.2 or * later kernels and libc5, and don't provide a * file; * * not all versions of glibc2 have a file * that defines stuff needed for some of the 2.4-or-later-kernel * features, so if the system has a 2.4 or later kernel, we * still can't use those features. * * We're already including a number of other headers, and * this code is Linux-specific (no other OS has PF_PACKET sockets as * a raw packet capture mechanism), so it's not as if you gain any * useful portability by using * * XXX - should we just include even if PF_PACKET * isn't defined? It only defines one data structure in 2.0.x, so * it shouldn't cause any problems. */ #ifdef PF_PACKET # include /* * On at least some Linux distributions (for example, Red Hat 5.2), * there's no file, but PF_PACKET is defined if * you include , but doesn't define * any of the PF_PACKET stuff such as "struct sockaddr_ll" or any of * the PACKET_xxx stuff. * * So we check whether PACKET_HOST is defined, and assume that we have * PF_PACKET sockets only if it is defined. */ # ifdef PACKET_HOST # define HAVE_PF_PACKET_SOCKETS # endif /* PACKET_HOST */ #endif /* PF_PACKET */ #ifdef SO_ATTACH_FILTER #include #include #endif #ifndef __GLIBC__ typedef int socklen_t; #endif #ifndef MSG_TRUNC /* * This is being compiled on a system that lacks MSG_TRUNC; define it * with the value it has in the 2.2 and later kernels, so that, on * those kernels, when we pass it in the flags argument to "recvfrom()" * we're passing the right value and thus get the MSG_TRUNC behavior * we want. (We don't get that behavior on 2.0[.x] kernels, because * they didn't support MSG_TRUNC.) */ #define MSG_TRUNC 0x20 #endif #ifndef SOL_PACKET /* * This is being compiled on a system that lacks SOL_PACKET; define it * with the value it has in the 2.2 and later kernels, so that we can * set promiscuous mode in the good modern way rather than the old * 2.0-kernel crappy way. */ #define SOL_PACKET 263 #endif #define MAX_LINKHEADER_SIZE 256 /* * When capturing on all interfaces we use this as the buffer size. * Should be bigger then all MTUs that occur in real life. * 64kB should be enough for now. */ #define BIGGER_THAN_ALL_MTUS (64*1024) /* * Prototypes for internal functions */ static void map_arphrd_to_dlt(pcap_t *, int, int); static int live_open_old(pcap_t *, const char *, int, int, char *); static int live_open_new(pcap_t *, const char *, int, int, char *); static int pcap_read_linux(pcap_t *, int, pcap_handler, u_char *); static int pcap_read_packet(pcap_t *, pcap_handler, u_char *); static int pcap_stats_linux(pcap_t *, struct pcap_stat *); static int pcap_setfilter_linux(pcap_t *, struct bpf_program *); static void pcap_close_linux(pcap_t *); /* * Wrap some ioctl calls */ #ifdef HAVE_PF_PACKET_SOCKETS static int iface_get_id(int fd, const char *device, char *ebuf); #endif static int iface_get_mtu(int fd, const char *device, char *ebuf); static int iface_get_arptype(int fd, const char *device, char *ebuf); #ifdef HAVE_PF_PACKET_SOCKETS static int iface_bind(int fd, int ifindex, char *ebuf); #endif static int iface_bind_old(int fd, const char *device, char *ebuf); #ifdef SO_ATTACH_FILTER static int fix_program(pcap_t *handle, struct sock_fprog *fcode); static int fix_offset(struct bpf_insn *p); static int set_kernel_filter(pcap_t *handle, struct sock_fprog *fcode); static int reset_kernel_filter(pcap_t *handle); static struct sock_filter total_insn = BPF_STMT(BPF_RET | BPF_K, 0); static struct sock_fprog total_fcode = { 1, &total_insn }; #endif /* * Get a handle for a live capture from the given device. You can * pass NULL as device to get all packages (without link level * information of course). If you pass 1 as promisc the interface * will be set to promiscous mode (XXX: I think this usage should * be deprecated and functions be added to select that later allow * modification of that values -- Torsten). * * See also pcap(3). */ pcap_t * pcap_open_live(const char *device, int snaplen, int promisc, int to_ms, char *ebuf) { pcap_t *handle; int mtu; int err; int live_open_ok = 0; struct utsname utsname; #ifdef HAVE_DAG_API if (strstr(device, "dag")) { return dag_open_live(device, snaplen, promisc, to_ms, ebuf); } #endif /* HAVE_DAG_API */ /* Allocate a handle for this session. */ handle = malloc(sizeof(*handle)); if (handle == NULL) { snprintf(ebuf, PCAP_ERRBUF_SIZE, "malloc: %s", pcap_strerror(errno)); return NULL; } /* Initialize some components of the pcap structure. */ memset(handle, 0, sizeof(*handle)); handle->snapshot = snaplen; handle->md.timeout = to_ms; /* * NULL and "any" are special devices which give us the hint to * monitor all devices. */ if (!device || strcmp(device, "any") == 0) { device = NULL; handle->md.device = strdup("any"); if (promisc) { promisc = 0; /* Just a warning. */ snprintf(ebuf, PCAP_ERRBUF_SIZE, "Promiscuous mode not supported on the \"any\" device"); } } else handle->md.device = strdup(device); if (handle->md.device == NULL) { snprintf(ebuf, PCAP_ERRBUF_SIZE, "strdup: %s", pcap_strerror(errno) ); free(handle); return NULL; } /* * Current Linux kernels use the protocol family PF_PACKET to * allow direct access to all packets on the network while * older kernels had a special socket type SOCK_PACKET to * implement this feature. * While this old implementation is kind of obsolete we need * to be compatible with older kernels for a while so we are * trying both methods with the newer method preferred. */ if ((err = live_open_new(handle, device, promisc, to_ms, ebuf)) == 1) live_open_ok = 1; else if (err == 0) { /* Non-fatal error; try old way */ if (live_open_old(handle, device, promisc, to_ms, ebuf)) live_open_ok = 1; } if (!live_open_ok) { /* * Both methods to open the packet socket failed. Tidy * up and report our failure (ebuf is expected to be * set by the functions above). */ if (handle->md.device != NULL) free(handle->md.device); free(handle); return NULL; } /* * Compute the buffer size. * * If we're using SOCK_PACKET, this might be a 2.0[.x] kernel, * and might require special handling - check. */ if (handle->md.sock_packet && (uname(&utsname) < 0 || strncmp(utsname.release, "2.0", 3) == 0)) { /* * We're using a SOCK_PACKET structure, and either * we couldn't find out what kernel release this is, * or it's a 2.0[.x] kernel. * * In the 2.0[.x] kernel, a "recvfrom()" on * a SOCK_PACKET socket, with MSG_TRUNC set, will * return the number of bytes read, so if we pass * a length based on the snapshot length, it'll * return the number of bytes from the packet * copied to userland, not the actual length * of the packet. * * This means that, for example, the IP dissector * in tcpdump will get handed a packet length less * than the length in the IP header, and will * complain about "truncated-ip". * * So we don't bother trying to copy from the * kernel only the bytes in which we're interested, * but instead copy them all, just as the older * versions of libpcap for Linux did. * * The buffer therefore needs to be big enough to * hold the largest packet we can get from this * device. Unfortunately, we can't get the MRU * of the network; we can only get the MTU. The * MTU may be too small, in which case a packet larger * than the buffer size will be truncated *and* we * won't get the actual packet size. * * However, if the snapshot length is larger than * the buffer size based on the MTU, we use the * snapshot length as the buffer size, instead; * this means that with a sufficiently large snapshot * length we won't artificially truncate packets * to the MTU-based size. * * This mess just one of many problems with packet * capture on 2.0[.x] kernels; you really want a * 2.2[.x] or later kernel if you want packet capture * to work well. */ mtu = iface_get_mtu(handle->fd, device, ebuf); if (mtu == -1) { pcap_close_linux(handle); free(handle); return NULL; } handle->bufsize = MAX_LINKHEADER_SIZE + mtu; if (handle->bufsize < handle->snapshot) handle->bufsize = handle->snapshot; } else { /* * This is a 2.2[.x] or later kernel (we know that * either because we're not using a SOCK_PACKET * socket - PF_PACKET is supported only in 2.2 * and later kernels - or because we checked the * kernel version). * * We can safely pass "recvfrom()" a byte count * based on the snapshot length. */ handle->bufsize = handle->snapshot; } /* Allocate the buffer */ handle->buffer = malloc(handle->bufsize + handle->offset); if (!handle->buffer) { snprintf(ebuf, PCAP_ERRBUF_SIZE, "malloc: %s", pcap_strerror(errno)); pcap_close_linux(handle); free(handle); return NULL; } /* * "handle->fd" is a socket, so "select()" and "poll()" * should work on it. */ handle->selectable_fd = handle->fd; handle->read_op = pcap_read_linux; handle->setfilter_op = pcap_setfilter_linux; handle->set_datalink_op = NULL; /* can't change data link type */ handle->getnonblock_op = pcap_getnonblock_fd; handle->setnonblock_op = pcap_setnonblock_fd; handle->stats_op = pcap_stats_linux; handle->close_op = pcap_close_linux; return handle; } /* * Read at most max_packets from the capture stream and call the callback * for each of them. Returns the number of packets handled or -1 if an * error occured. */ static int pcap_read_linux(pcap_t *handle, int max_packets, pcap_handler callback, u_char *user) { /* * Currently, on Linux only one packet is delivered per read, * so we don't loop. */ return pcap_read_packet(handle, callback, user); } /* * Read a packet from the socket calling the handler provided by * the user. Returns the number of packets received or -1 if an * error occured. */ static int pcap_read_packet(pcap_t *handle, pcap_handler callback, u_char *userdata) { u_char *bp; int offset; #ifdef HAVE_PF_PACKET_SOCKETS struct sockaddr_ll from; struct sll_header *hdrp; #else struct sockaddr from; #endif socklen_t fromlen; int packet_len, caplen; struct pcap_pkthdr pcap_header; #ifdef HAVE_PF_PACKET_SOCKETS /* * If this is a cooked device, leave extra room for a * fake packet header. */ if (handle->md.cooked) offset = SLL_HDR_LEN; else offset = 0; #else /* * This system doesn't have PF_PACKET sockets, so it doesn't * support cooked devices. */ offset = 0; #endif /* Receive a single packet from the kernel */ bp = handle->buffer + handle->offset; do { /* * Has "pcap_breakloop()" been called? */ if (handle->break_loop) { /* * Yes - clear the flag that indicates that it * has, and return -2 as an indication that we * were told to break out of the loop. */ handle->break_loop = 0; return -2; } fromlen = sizeof(from); packet_len = recvfrom( handle->fd, bp + offset, handle->bufsize - offset, MSG_TRUNC, (struct sockaddr *) &from, &fromlen); } while (packet_len == -1 && errno == EINTR); /* Check if an error occured */ if (packet_len == -1) { if (errno == EAGAIN) return 0; /* no packet there */ else { snprintf(handle->errbuf, sizeof(handle->errbuf), "recvfrom: %s", pcap_strerror(errno)); return -1; } } #ifdef HAVE_PF_PACKET_SOCKETS /* * If this is from the loopback device, reject outgoing packets; * we'll see the packet as an incoming packet as well, and * we don't want to see it twice. * * We can only do this if we're using PF_PACKET; the address * returned for SOCK_PACKET is a "sockaddr_pkt" which lacks * the relevant packet type information. */ if (!handle->md.sock_packet && from.sll_ifindex == handle->md.lo_ifindex && from.sll_pkttype == PACKET_OUTGOING) return 0; #endif #ifdef HAVE_PF_PACKET_SOCKETS /* * If this is a cooked device, fill in the fake packet header. */ if (handle->md.cooked) { /* * Add the length of the fake header to the length * of packet data we read. */ packet_len += SLL_HDR_LEN; hdrp = (struct sll_header *)bp; /* * Map the PACKET_ value to a LINUX_SLL_ value; we * want the same numerical value to be used in * the link-layer header even if the numerical values * for the PACKET_ #defines change, so that programs * that look at the packet type field will always be * able to handle DLT_LINUX_SLL captures. */ switch (from.sll_pkttype) { case PACKET_HOST: hdrp->sll_pkttype = htons(LINUX_SLL_HOST); break; case PACKET_BROADCAST: hdrp->sll_pkttype = htons(LINUX_SLL_BROADCAST); break; case PACKET_MULTICAST: hdrp->sll_pkttype = htons(LINUX_SLL_MULTICAST); break; case PACKET_OTHERHOST: hdrp->sll_pkttype = htons(LINUX_SLL_OTHERHOST); break; case PACKET_OUTGOING: hdrp->sll_pkttype = htons(LINUX_SLL_OUTGOING); break; default: hdrp->sll_pkttype = -1; break; } hdrp->sll_hatype = htons(from.sll_hatype); hdrp->sll_halen = htons(from.sll_halen); memcpy(hdrp->sll_addr, from.sll_addr, (from.sll_halen > SLL_ADDRLEN) ? SLL_ADDRLEN : from.sll_halen); hdrp->sll_protocol = from.sll_protocol; } #endif /* * XXX: According to the kernel source we should get the real * packet len if calling recvfrom with MSG_TRUNC set. It does * not seem to work here :(, but it is supported by this code * anyway. * To be honest the code RELIES on that feature so this is really * broken with 2.2.x kernels. * I spend a day to figure out what's going on and I found out * that the following is happening: * * The packet comes from a random interface and the packet_rcv * hook is called with a clone of the packet. That code inserts * the packet into the receive queue of the packet socket. * If a filter is attached to that socket that filter is run * first - and there lies the problem. The default filter always * cuts the packet at the snaplen: * * # tcpdump -d * (000) ret #68 * * So the packet filter cuts down the packet. The recvfrom call * says "hey, it's only 68 bytes, it fits into the buffer" with * the result that we don't get the real packet length. This * is valid at least until kernel 2.2.17pre6. * * We currently handle this by making a copy of the filter * program, fixing all "ret" instructions with non-zero * operands to have an operand of 65535 so that the filter * doesn't truncate the packet, and supplying that modified * filter to the kernel. */ caplen = packet_len; if (caplen > handle->snapshot) caplen = handle->snapshot; /* Run the packet filter if not using kernel filter */ if (!handle->md.use_bpf && handle->fcode.bf_insns) { if (bpf_filter(handle->fcode.bf_insns, bp, packet_len, caplen) == 0) { /* rejected by filter */ return 0; } } /* Fill in our own header data */ if (ioctl(handle->fd, SIOCGSTAMP, &pcap_header.ts) == -1) { snprintf(handle->errbuf, sizeof(handle->errbuf), "ioctl: %s", pcap_strerror(errno)); return -1; } pcap_header.caplen = caplen; pcap_header.len = packet_len; /* * Count the packet. * * Arguably, we should count them before we check the filter, * as on many other platforms "ps_recv" counts packets * handed to the filter rather than packets that passed * the filter, but if filtering is done in the kernel, we * can't get a count of packets that passed the filter, * and that would mean the meaning of "ps_recv" wouldn't * be the same on all Linux systems. * * XXX - it's not the same on all systems in any case; * ideally, we should have a "get the statistics" call * that supplies more counts and indicates which of them * it supplies, so that we supply a count of packets * handed to the filter only on platforms where that * information is available. * * We count them here even if we can get the packet count * from the kernel, as we can only determine at run time * whether we'll be able to get it from the kernel (if * HAVE_TPACKET_STATS isn't defined, we can't get it from * the kernel, but if it is defined, the library might * have been built with a 2.4 or later kernel, but we * might be running on a 2.2[.x] kernel without Alexey * Kuznetzov's turbopacket patches, and thus the kernel * might not be able to supply those statistics). We * could, I guess, try, when opening the socket, to get * the statistics, and if we can not increment the count * here, but it's not clear that always incrementing * the count is more expensive than always testing a flag * in memory. */ handle->md.stat.ps_recv++; /* Call the user supplied callback function */ callback(userdata, &pcap_header, bp); return 1; } /* * Get the statistics for the given packet capture handle. * Reports the number of dropped packets iff the kernel supports * the PACKET_STATISTICS "getsockopt()" argument (2.4 and later * kernels, and 2.2[.x] kernels with Alexey Kuznetzov's turbopacket * patches); otherwise, that information isn't available, and we lie * and report 0 as the count of dropped packets. */ static int pcap_stats_linux(pcap_t *handle, struct pcap_stat *stats) { #ifdef HAVE_TPACKET_STATS struct tpacket_stats kstats; socklen_t len = sizeof (struct tpacket_stats); #endif #ifdef HAVE_TPACKET_STATS /* * Try to get the packet counts from the kernel. */ if (getsockopt(handle->fd, SOL_PACKET, PACKET_STATISTICS, &kstats, &len) > -1) { /* * In "linux/net/packet/af_packet.c", at least in the * 2.4.9 kernel, "tp_packets" is incremented for every * packet that passes the packet filter *and* is * successfully queued on the socket; "tp_drops" is * incremented for every packet dropped because there's * not enough free space in the socket buffer. * * When the statistics are returned for a PACKET_STATISTICS * "getsockopt()" call, "tp_drops" is added to "tp_packets", * so that "tp_packets" counts all packets handed to * the PF_PACKET socket, including packets dropped because * there wasn't room on the socket buffer - but not * including packets that didn't pass the filter. * * In the BSD BPF, the count of received packets is * incremented for every packet handed to BPF, regardless * of whether it passed the filter. * * We can't make "pcap_stats()" work the same on both * platforms, but the best approximation is to return * "tp_packets" as the count of packets and "tp_drops" * as the count of drops. */ handle->md.stat.ps_recv = kstats.tp_packets; handle->md.stat.ps_drop = kstats.tp_drops; } else { /* * If the error was EOPNOTSUPP, fall through, so that * if you build the library on a system with * "struct tpacket_stats" and run it on a system * that doesn't, it works as it does if the library * is built on a system without "struct tpacket_stats". */ if (errno != EOPNOTSUPP) { snprintf(handle->errbuf, PCAP_ERRBUF_SIZE, "pcap_stats: %s", pcap_strerror(errno)); return -1; } } #endif /* * On systems where the PACKET_STATISTICS "getsockopt()" argument * is supported on PF_PACKET sockets: * * "ps_recv" counts only packets that *passed* the filter, * not packets that didn't pass the filter. This includes * packets later dropped because we ran out of buffer space. * * "ps_drop" counts packets dropped because we ran out of * buffer space. It doesn't count packets dropped by the * interface driver. It counts only packets that passed * the filter. * * Both statistics include packets not yet read from the * kernel by libpcap, and thus not yet seen by the application. * * On systems where the PACKET_STATISTICS "getsockopt()" argument * is not supported on PF_PACKET sockets: * * "ps_recv" counts only packets that *passed* the filter, * not packets that didn't pass the filter. It does not * count packets dropped because we ran out of buffer * space. * * "ps_drop" is not supported. * * "ps_recv" doesn't include packets not yet read from * the kernel by libpcap. */ *stats = handle->md.stat; return 0; } /* * Description string for the "any" device. */ static const char any_descr[] = "Pseudo-device that captures on all interfaces"; int pcap_platform_finddevs(pcap_if_t **alldevsp, char *errbuf) { if (pcap_add_if(alldevsp, "any", 0, any_descr, errbuf) < 0) return (-1); #ifdef HAVE_DAG_API if (dag_platform_finddevs(alldevsp, errbuf) < 0) return (-1); #endif /* HAVE_DAG_API */ return (0); } /* * Attach the given BPF code to the packet capture device. */ static int pcap_setfilter_linux(pcap_t *handle, struct bpf_program *filter) { #ifdef SO_ATTACH_FILTER struct sock_fprog fcode; int can_filter_in_kernel; int err = 0; #endif if (!handle) return -1; if (!filter) { strncpy(handle->errbuf, "setfilter: No filter specified", sizeof(handle->errbuf)); return -1; } /* Make our private copy of the filter */ if (install_bpf_program(handle, filter) < 0) /* install_bpf_program() filled in errbuf */ return -1; /* * Run user level packet filter by default. Will be overriden if * installing a kernel filter succeeds. */ handle->md.use_bpf = 0; /* Install kernel level filter if possible */ #ifdef SO_ATTACH_FILTER #ifdef USHRT_MAX if (handle->fcode.bf_len > USHRT_MAX) { /* * fcode.len is an unsigned short for current kernel. * I have yet to see BPF-Code with that much * instructions but still it is possible. So for the * sake of correctness I added this check. */ fprintf(stderr, "Warning: Filter too complex for kernel\n"); fcode.filter = NULL; can_filter_in_kernel = 0; } else #endif /* USHRT_MAX */ { /* * Oh joy, the Linux kernel uses struct sock_fprog instead * of struct bpf_program and of course the length field is * of different size. Pointed out by Sebastian * * Oh, and we also need to fix it up so that all "ret" * instructions with non-zero operands have 65535 as the * operand, and so that, if we're in cooked mode, all * memory-reference instructions use special magic offsets * in references to the link-layer header and assume that * the link-layer payload begins at 0; "fix_program()" * will do that. */ switch (fix_program(handle, &fcode)) { case -1: default: /* * Fatal error; just quit. * (The "default" case shouldn't happen; we * return -1 for that reason.) */ return -1; case 0: /* * The program performed checks that we can't make * work in the kernel. */ can_filter_in_kernel = 0; break; case 1: /* * We have a filter that'll work in the kernel. */ can_filter_in_kernel = 1; break; } } if (can_filter_in_kernel) { if ((err = set_kernel_filter(handle, &fcode)) == 0) { /* Installation succeded - using kernel filter. */ handle->md.use_bpf = 1; } else if (err == -1) /* Non-fatal error */ { /* * Print a warning if we weren't able to install * the filter for a reason other than "this kernel * isn't configured to support socket filters. */ if (errno != ENOPROTOOPT && errno != EOPNOTSUPP) { fprintf(stderr, "Warning: Kernel filter failed: %s\n", pcap_strerror(errno)); } } } /* * If we're not using the kernel filter, get rid of any kernel * filter that might've been there before, e.g. because the * previous filter could work in the kernel, or because some other * code attached a filter to the socket by some means other than * calling "pcap_setfilter()". Otherwise, the kernel filter may * filter out packets that would pass the new userland filter. */ if (!handle->md.use_bpf) reset_kernel_filter(handle); /* * Free up the copy of the filter that was made by "fix_program()". */ if (fcode.filter != NULL) free(fcode.filter); if (err == -2) /* Fatal error */ return -1; #endif /* SO_ATTACH_FILTER */ return 0; } /* * Linux uses the ARP hardware type to identify the type of an * interface. pcap uses the DLT_xxx constants for this. This * function takes a pointer to a "pcap_t", and an ARPHRD_xxx * constant, as arguments, and sets "handle->linktype" to the * appropriate DLT_XXX constant and sets "handle->offset" to * the appropriate value (to make "handle->offset" plus link-layer * header length be a multiple of 4, so that the link-layer payload * will be aligned on a 4-byte boundary when capturing packets). * (If the offset isn't set here, it'll be 0; add code as appropriate * for cases where it shouldn't be 0.) * * If "cooked_ok" is non-zero, we can use DLT_LINUX_SLL and capture * in cooked mode; otherwise, we can't use cooked mode, so we have * to pick some type that works in raw mode, or fail. * * Sets the link type to -1 if unable to map the type. */ static void map_arphrd_to_dlt(pcap_t *handle, int arptype, int cooked_ok) { switch (arptype) { case ARPHRD_ETHER: case ARPHRD_METRICOM: case ARPHRD_LOOPBACK: handle->linktype = DLT_EN10MB; handle->offset = 2; break; case ARPHRD_EETHER: handle->linktype = DLT_EN3MB; break; case ARPHRD_AX25: handle->linktype = DLT_AX25; break; case ARPHRD_PRONET: handle->linktype = DLT_PRONET; break; case ARPHRD_CHAOS: handle->linktype = DLT_CHAOS; break; #ifndef ARPHRD_IEEE802_TR #define ARPHRD_IEEE802_TR 800 /* From Linux 2.4 */ #endif case ARPHRD_IEEE802_TR: case ARPHRD_IEEE802: handle->linktype = DLT_IEEE802; handle->offset = 2; break; case ARPHRD_ARCNET: handle->linktype = DLT_ARCNET_LINUX; break; #ifndef ARPHRD_FDDI /* From Linux 2.2.13 */ #define ARPHRD_FDDI 774 #endif case ARPHRD_FDDI: handle->linktype = DLT_FDDI; handle->offset = 3; break; #ifndef ARPHRD_ATM /* FIXME: How to #include this? */ #define ARPHRD_ATM 19 #endif case ARPHRD_ATM: /* * The Classical IP implementation in ATM for Linux * supports both what RFC 1483 calls "LLC Encapsulation", * in which each packet has an LLC header, possibly * with a SNAP header as well, prepended to it, and * what RFC 1483 calls "VC Based Multiplexing", in which * different virtual circuits carry different network * layer protocols, and no header is prepended to packets. * * They both have an ARPHRD_ type of ARPHRD_ATM, so * you can't use the ARPHRD_ type to find out whether * captured packets will have an LLC header, and, * while there's a socket ioctl to *set* the encapsulation * type, there's no ioctl to *get* the encapsulation type. * * This means that * * programs that dissect Linux Classical IP frames * would have to check for an LLC header and, * depending on whether they see one or not, dissect * the frame as LLC-encapsulated or as raw IP (I * don't know whether there's any traffic other than * IP that would show up on the socket, or whether * there's any support for IPv6 in the Linux * Classical IP code); * * filter expressions would have to compile into * code that checks for an LLC header and does * the right thing. * * Both of those are a nuisance - and, at least on systems * that support PF_PACKET sockets, we don't have to put * up with those nuisances; instead, we can just capture * in cooked mode. That's what we'll do, if we can. * Otherwise, we'll just fail. */ if (cooked_ok) handle->linktype = DLT_LINUX_SLL; else handle->linktype = -1; break; #ifndef ARPHRD_IEEE80211 /* From Linux 2.4.6 */ #define ARPHRD_IEEE80211 801 #endif case ARPHRD_IEEE80211: handle->linktype = DLT_IEEE802_11; break; #ifndef ARPHRD_IEEE80211_PRISM /* From Linux 2.4.18 */ #define ARPHRD_IEEE80211_PRISM 802 #endif case ARPHRD_IEEE80211_PRISM: handle->linktype = DLT_PRISM_HEADER; break; case ARPHRD_PPP: /* * Some PPP code in the kernel supplies no link-layer * header whatsoever to PF_PACKET sockets; other PPP * code supplies PPP link-layer headers ("syncppp.c"); * some PPP code might supply random link-layer * headers (PPP over ISDN - there's code in Ethereal, * for example, to cope with PPP-over-ISDN captures * with which the Ethereal developers have had to cope, * heuristically trying to determine which of the * oddball link-layer headers particular packets have). * * As such, we just punt, and run all PPP interfaces * in cooked mode, if we can; otherwise, we just treat * it as DLT_RAW, for now - if somebody needs to capture, * on a 2.0[.x] kernel, on PPP devices that supply a * link-layer header, they'll have to add code here to * map to the appropriate DLT_ type (possibly adding a * new DLT_ type, if necessary). */ if (cooked_ok) handle->linktype = DLT_LINUX_SLL; else { /* * XXX - handle ISDN types here? We can't fall * back on cooked sockets, so we'd have to * figure out from the device name what type of * link-layer encapsulation it's using, and map * that to an appropriate DLT_ value, meaning * we'd map "isdnN" devices to DLT_RAW (they * supply raw IP packets with no link-layer * header) and "isdY" devices to a new DLT_I4L_IP * type that has only an Ethernet packet type as * a link-layer header. * * But sometimes we seem to get random crap * in the link-layer header when capturing on * ISDN devices.... */ handle->linktype = DLT_RAW; } break; #ifndef ARPHRD_CISCO #define ARPHRD_CISCO 513 /* previously ARPHRD_HDLC */ #endif case ARPHRD_CISCO: handle->linktype = DLT_C_HDLC; break; /* Not sure if this is correct for all tunnels, but it * works for CIPE */ case ARPHRD_TUNNEL: #ifndef ARPHRD_SIT #define ARPHRD_SIT 776 /* From Linux 2.2.13 */ #endif case ARPHRD_SIT: case ARPHRD_CSLIP: case ARPHRD_SLIP6: case ARPHRD_CSLIP6: case ARPHRD_ADAPT: case ARPHRD_SLIP: #ifndef ARPHRD_RAWHDLC #define ARPHRD_RAWHDLC 518 #endif case ARPHRD_RAWHDLC: #ifndef ARPHRD_DLCI #define ARPHRD_DLCI 15 #endif case ARPHRD_DLCI: /* * XXX - should some of those be mapped to DLT_LINUX_SLL * instead? Should we just map all of them to DLT_LINUX_SLL? */ handle->linktype = DLT_RAW; break; #ifndef ARPHRD_FRAD #define ARPHRD_FRAD 770 #endif case ARPHRD_FRAD: handle->linktype = DLT_FRELAY; break; case ARPHRD_LOCALTLK: handle->linktype = DLT_LTALK; break; #ifndef ARPHRD_FCPP #define ARPHRD_FCPP 784 #endif case ARPHRD_FCPP: #ifndef ARPHRD_FCAL #define ARPHRD_FCAL 785 #endif case ARPHRD_FCAL: #ifndef ARPHRD_FCPL #define ARPHRD_FCPL 786 #endif case ARPHRD_FCPL: #ifndef ARPHRD_FCFABRIC #define ARPHRD_FCFABRIC 787 #endif case ARPHRD_FCFABRIC: /* * We assume that those all mean RFC 2625 IP-over- * Fibre Channel, with the RFC 2625 header at * the beginning of the packet. */ handle->linktype = DLT_IP_OVER_FC; break; case ARPHRD_IRDA: /* Don't expect IP packet out of this interfaces... */ handle->linktype = DLT_LINUX_IRDA; /* We need to save packet direction for IrDA decoding, * so let's use "Linux-cooked" mode. Jean II */ //handle->md.cooked = 1; break; default: handle->linktype = -1; break; } } /* ===== Functions to interface to the newer kernels ================== */ /* * Try to open a packet socket using the new kernel interface. * Returns 0 on failure. * FIXME: 0 uses to mean success (Sebastian) */ static int live_open_new(pcap_t *handle, const char *device, int promisc, int to_ms, char *ebuf) { #ifdef HAVE_PF_PACKET_SOCKETS int sock_fd = -1, device_id, arptype; int err; int fatal_err = 0; struct packet_mreq mr; /* One shot loop used for error handling - bail out with break */ do { /* * Open a socket with protocol family packet. If a device is * given we try to open it in raw mode otherwise we use * the cooked interface. */ sock_fd = device ? socket(PF_PACKET, SOCK_RAW, htons(ETH_P_ALL)) : socket(PF_PACKET, SOCK_DGRAM, htons(ETH_P_ALL)); if (sock_fd == -1) { snprintf(ebuf, PCAP_ERRBUF_SIZE, "socket: %s", pcap_strerror(errno) ); break; } /* It seems the kernel supports the new interface. */ handle->md.sock_packet = 0; /* * Get the interface index of the loopback device. * If the attempt fails, don't fail, just set the * "md.lo_ifindex" to -1. * * XXX - can there be more than one device that loops * packets back, i.e. devices other than "lo"? If so, * we'd need to find them all, and have an array of * indices for them, and check all of them in * "pcap_read_packet()". */ handle->md.lo_ifindex = iface_get_id(sock_fd, "lo", ebuf); /* * Default value for offset to align link-layer payload * on a 4-byte boundary. */ handle->offset = 0; /* * What kind of frames do we have to deal with? Fall back * to cooked mode if we have an unknown interface type. */ if (device) { /* Assume for now we don't need cooked mode. */ handle->md.cooked = 0; arptype = iface_get_arptype(sock_fd, device, ebuf); if (arptype == -1) { fatal_err = 1; break; } map_arphrd_to_dlt(handle, arptype, 1); if (handle->linktype == -1 || handle->linktype == DLT_LINUX_SLL || handle->linktype == DLT_LINUX_IRDA || (handle->linktype == DLT_EN10MB && (strncmp("isdn", device, 4) == 0 || strncmp("isdY", device, 4) == 0))) { /* * Unknown interface type (-1), or a * device we explicitly chose to run * in cooked mode (e.g., PPP devices), * or an ISDN device (whose link-layer * type we can only determine by using * APIs that may be different on different * kernels) - reopen in cooked mode. */ if (close(sock_fd) == -1) { snprintf(ebuf, PCAP_ERRBUF_SIZE, "close: %s", pcap_strerror(errno)); break; } sock_fd = socket(PF_PACKET, SOCK_DGRAM, htons(ETH_P_ALL)); if (sock_fd == -1) { snprintf(ebuf, PCAP_ERRBUF_SIZE, "socket: %s", pcap_strerror(errno)); break; } handle->md.cooked = 1; if (handle->linktype == -1) { /* * Warn that we're falling back on * cooked mode; we may want to * update "map_arphrd_to_dlt()" * to handle the new type. */ snprintf(ebuf, PCAP_ERRBUF_SIZE, "arptype %d not " "supported by libpcap - " "falling back to cooked " "socket", arptype); } /* IrDA capture is not a real "cooked" capture, * it's IrLAP frames, not IP packets. */ if(handle->linktype != DLT_LINUX_IRDA) handle->linktype = DLT_LINUX_SLL; } device_id = iface_get_id(sock_fd, device, ebuf); if (device_id == -1) break; if ((err = iface_bind(sock_fd, device_id, ebuf)) < 0) { if (err == -2) fatal_err = 1; break; } } else { /* * This is cooked mode. */ handle->md.cooked = 1; handle->linktype = DLT_LINUX_SLL; /* * XXX - squelch GCC complaints about * uninitialized variables; if we can't * select promiscuous mode on all interfaces, * we should move the code below into the * "if (device)" branch of the "if" and * get rid of the next statement. */ device_id = -1; } /* * Select promiscuous mode on if "promisc" is set. * * Do not turn allmulti mode on if we don't select * promiscuous mode - on some devices (e.g., Orinoco * wireless interfaces), allmulti mode isn't supported * and the driver implements it by turning promiscuous * mode on, and that screws up the operation of the * card as a normal networking interface, and on no * other platform I know of does starting a non- * promiscuous capture affect which multicast packets * are received by the interface. */ /* * Hmm, how can we set promiscuous mode on all interfaces? * I am not sure if that is possible at all. */ if (device && promisc) { memset(&mr, 0, sizeof(mr)); mr.mr_ifindex = device_id; mr.mr_type = PACKET_MR_PROMISC; if (setsockopt(sock_fd, SOL_PACKET, PACKET_ADD_MEMBERSHIP, &mr, sizeof(mr)) == -1) { snprintf(ebuf, PCAP_ERRBUF_SIZE, "setsockopt: %s", pcap_strerror(errno)); break; } } /* Save the socket FD in the pcap structure */ handle->fd = sock_fd; return 1; } while(0); if (sock_fd != -1) close(sock_fd); if (fatal_err) return -2; else return 0; #else strncpy(ebuf, "New packet capturing interface not supported by build " "environment", PCAP_ERRBUF_SIZE); return 0; #endif } #ifdef HAVE_PF_PACKET_SOCKETS /* * Return the index of the given device name. Fill ebuf and return * -1 on failure. */ static int iface_get_id(int fd, const char *device, char *ebuf) { struct ifreq ifr; memset(&ifr, 0, sizeof(ifr)); strncpy(ifr.ifr_name, device, sizeof(ifr.ifr_name)); if (ioctl(fd, SIOCGIFINDEX, &ifr) == -1) { snprintf(ebuf, PCAP_ERRBUF_SIZE, "ioctl: %s", pcap_strerror(errno)); return -1; } return ifr.ifr_ifindex; } /* * Bind the socket associated with FD to the given device. */ static int iface_bind(int fd, int ifindex, char *ebuf) { struct sockaddr_ll sll; int err; socklen_t errlen = sizeof(err); memset(&sll, 0, sizeof(sll)); sll.sll_family = AF_PACKET; sll.sll_ifindex = ifindex; sll.sll_protocol = htons(ETH_P_ALL); if (bind(fd, (struct sockaddr *) &sll, sizeof(sll)) == -1) { snprintf(ebuf, PCAP_ERRBUF_SIZE, "bind: %s", pcap_strerror(errno)); return -1; } /* Any pending errors, e.g., network is down? */ if (getsockopt(fd, SOL_SOCKET, SO_ERROR, &err, &errlen) == -1) { snprintf(ebuf, PCAP_ERRBUF_SIZE, "getsockopt: %s", pcap_strerror(errno)); return -2; } if (err > 0) { snprintf(ebuf, PCAP_ERRBUF_SIZE, "bind: %s", pcap_strerror(err)); return -2; } return 0; } #endif /* ===== Functions to interface to the older kernels ================== */ /* * With older kernels promiscuous mode is kind of interesting because we * have to reset the interface before exiting. The problem can't really * be solved without some daemon taking care of managing usage counts. * If we put the interface into promiscuous mode, we set a flag indicating * that we must take it out of that mode when the interface is closed, * and, when closing the interface, if that flag is set we take it out * of promiscuous mode. */ /* * List of pcaps for which we turned promiscuous mode on by hand. * If there are any such pcaps, we arrange to call "pcap_close_all()" * when we exit, and have it close all of them to turn promiscuous mode * off. */ static struct pcap *pcaps_to_close; /* * TRUE if we've already called "atexit()" to cause "pcap_close_all()" to * be called on exit. */ static int did_atexit; static void pcap_close_all(void) { struct pcap *handle; while ((handle = pcaps_to_close) != NULL) pcap_close(handle); } static void pcap_close_linux( pcap_t *handle ) { struct pcap *p, *prevp; struct ifreq ifr; if (handle->md.clear_promisc) { /* * We put the interface into promiscuous mode; take * it out of promiscuous mode. * * XXX - if somebody else wants it in promiscuous mode, * this code cannot know that, so it'll take it out * of promiscuous mode. That's not fixable in 2.0[.x] * kernels. */ memset(&ifr, 0, sizeof(ifr)); strncpy(ifr.ifr_name, handle->md.device, sizeof(ifr.ifr_name)); if (ioctl(handle->fd, SIOCGIFFLAGS, &ifr) == -1) { fprintf(stderr, "Can't restore interface flags (SIOCGIFFLAGS failed: %s).\n" "Please adjust manually.\n" "Hint: This can't happen with Linux >= 2.2.0.\n", strerror(errno)); } else { if (ifr.ifr_flags & IFF_PROMISC) { /* * Promiscuous mode is currently on; turn it * off. */ ifr.ifr_flags &= ~IFF_PROMISC; if (ioctl(handle->fd, SIOCSIFFLAGS, &ifr) == -1) { fprintf(stderr, "Can't restore interface flags (SIOCSIFFLAGS failed: %s).\n" "Please adjust manually.\n" "Hint: This can't happen with Linux >= 2.2.0.\n", strerror(errno)); } } } /* * Take this pcap out of the list of pcaps for which we * have to take the interface out of promiscuous mode. */ for (p = pcaps_to_close, prevp = NULL; p != NULL; prevp = p, p = p->md.next) { if (p == handle) { /* * Found it. Remove it from the list. */ if (prevp == NULL) { /* * It was at the head of the list. */ pcaps_to_close = p->md.next; } else { /* * It was in the middle of the list. */ prevp->md.next = p->md.next; } break; } } } if (handle->md.device != NULL) free(handle->md.device); handle->md.device = NULL; if (handle->buffer != NULL) free(handle->buffer); if (handle->fd >= 0) close(handle->fd); } /* * Try to open a packet socket using the old kernel interface. * Returns 0 on failure. * FIXME: 0 uses to mean success (Sebastian) */ static int live_open_old(pcap_t *handle, const char *device, int promisc, int to_ms, char *ebuf) { int arptype; struct ifreq ifr; do { /* Open the socket */ handle->fd = socket(PF_INET, SOCK_PACKET, htons(ETH_P_ALL)); if (handle->fd == -1) { snprintf(ebuf, PCAP_ERRBUF_SIZE, "socket: %s", pcap_strerror(errno)); break; } /* It worked - we are using the old interface */ handle->md.sock_packet = 1; /* ...which means we get the link-layer header. */ handle->md.cooked = 0; /* Bind to the given device */ if (!device) { strncpy(ebuf, "pcap_open_live: The \"any\" device isn't supported on 2.0[.x]-kernel systems", PCAP_ERRBUF_SIZE); break; } if (iface_bind_old(handle->fd, device, ebuf) == -1) break; /* * Try to get the link-layer type. */ arptype = iface_get_arptype(handle->fd, device, ebuf); if (arptype == -1) break; /* * Try to find the DLT_ type corresponding to that * link-layer type. */ map_arphrd_to_dlt(handle, arptype, 0); if (handle->linktype == -1) { snprintf(ebuf, PCAP_ERRBUF_SIZE, "unknown arptype %d", arptype); break; } /* Go to promisc mode if requested */ if (promisc) { memset(&ifr, 0, sizeof(ifr)); strncpy(ifr.ifr_name, device, sizeof(ifr.ifr_name)); if (ioctl(handle->fd, SIOCGIFFLAGS, &ifr) == -1) { snprintf(ebuf, PCAP_ERRBUF_SIZE, "ioctl: %s", pcap_strerror(errno)); break; } if ((ifr.ifr_flags & IFF_PROMISC) == 0) { /* * Promiscuous mode isn't currently on, * so turn it on, and remember that * we should turn it off when the * pcap_t is closed. */ /* * If we haven't already done so, arrange * to have "pcap_close_all()" called when * we exit. */ if (!did_atexit) { if (atexit(pcap_close_all) == -1) { /* * "atexit()" failed; don't * put the interface in * promiscuous mode, just * give up. */ strncpy(ebuf, "atexit failed", PCAP_ERRBUF_SIZE); break; } did_atexit = 1; } ifr.ifr_flags |= IFF_PROMISC; if (ioctl(handle->fd, SIOCSIFFLAGS, &ifr) == -1) { snprintf(ebuf, PCAP_ERRBUF_SIZE, "ioctl: %s", pcap_strerror(errno)); break; } handle->md.clear_promisc = 1; /* * Add this to the list of pcaps * to close when we exit. */ handle->md.next = pcaps_to_close; pcaps_to_close = handle; } } /* * Default value for offset to align link-layer payload * on a 4-byte boundary. */ handle->offset = 0; return 1; } while (0); pcap_close_linux(handle); return 0; } /* * Bind the socket associated with FD to the given device using the * interface of the old kernels. */ static int iface_bind_old(int fd, const char *device, char *ebuf) { struct sockaddr saddr; int err; socklen_t errlen = sizeof(err); memset(&saddr, 0, sizeof(saddr)); strncpy(saddr.sa_data, device, sizeof(saddr.sa_data)); if (bind(fd, &saddr, sizeof(saddr)) == -1) { snprintf(ebuf, PCAP_ERRBUF_SIZE, "bind: %s", pcap_strerror(errno)); return -1; } /* Any pending errors, e.g., network is down? */ if (getsockopt(fd, SOL_SOCKET, SO_ERROR, &err, &errlen) == -1) { snprintf(ebuf, PCAP_ERRBUF_SIZE, "getsockopt: %s", pcap_strerror(errno)); return -1; } if (err > 0) { snprintf(ebuf, PCAP_ERRBUF_SIZE, "bind: %s", pcap_strerror(err)); return -1; } return 0; } /* ===== System calls available on all supported kernels ============== */ /* * Query the kernel for the MTU of the given interface. */ static int iface_get_mtu(int fd, const char *device, char *ebuf) { struct ifreq ifr; if (!device) return BIGGER_THAN_ALL_MTUS; memset(&ifr, 0, sizeof(ifr)); strncpy(ifr.ifr_name, device, sizeof(ifr.ifr_name)); if (ioctl(fd, SIOCGIFMTU, &ifr) == -1) { snprintf(ebuf, PCAP_ERRBUF_SIZE, "ioctl: %s", pcap_strerror(errno)); return -1; } return ifr.ifr_mtu; } /* * Get the hardware type of the given interface as ARPHRD_xxx constant. */ static int iface_get_arptype(int fd, const char *device, char *ebuf) { struct ifreq ifr; memset(&ifr, 0, sizeof(ifr)); strncpy(ifr.ifr_name, device, sizeof(ifr.ifr_name)); if (ioctl(fd, SIOCGIFHWADDR, &ifr) == -1) { snprintf(ebuf, PCAP_ERRBUF_SIZE, "ioctl: %s", pcap_strerror(errno)); return -1; } return ifr.ifr_hwaddr.sa_family; } #ifdef SO_ATTACH_FILTER static int fix_program(pcap_t *handle, struct sock_fprog *fcode) { size_t prog_size; register int i; register struct bpf_insn *p; struct bpf_insn *f; int len; /* * Make a copy of the filter, and modify that copy if * necessary. */ prog_size = sizeof(*handle->fcode.bf_insns) * handle->fcode.bf_len; len = handle->fcode.bf_len; f = (struct bpf_insn *)malloc(prog_size); if (f == NULL) { snprintf(handle->errbuf, sizeof(handle->errbuf), "malloc: %s", pcap_strerror(errno)); return -1; } memcpy(f, handle->fcode.bf_insns, prog_size); fcode->len = len; fcode->filter = (struct sock_filter *) f; for (i = 0; i < len; ++i) { p = &f[i]; /* * What type of instruction is this? */ switch (BPF_CLASS(p->code)) { case BPF_RET: /* * It's a return instruction; is the snapshot * length a constant, rather than the contents * of the accumulator? */ if (BPF_MODE(p->code) == BPF_K) { /* * Yes - if the value to be returned, * i.e. the snapshot length, is anything * other than 0, make it 65535, so that * the packet is truncated by "recvfrom()", * not by the filter. * * XXX - there's nothing we can easily do * if it's getting the value from the * accumulator; we'd have to insert * code to force non-zero values to be * 65535. */ if (p->k != 0) p->k = 65535; } break; case BPF_LD: case BPF_LDX: /* * It's a load instruction; is it loading * from the packet? */ switch (BPF_MODE(p->code)) { case BPF_ABS: case BPF_IND: case BPF_MSH: /* * Yes; are we in cooked mode? */ if (handle->md.cooked) { /* * Yes, so we need to fix this * instruction. */ if (fix_offset(p) < 0) { /* * We failed to do so. * Return 0, so our caller * knows to punt to userland. */ return 0; } } break; } break; } } return 1; /* we succeeded */ } static int fix_offset(struct bpf_insn *p) { /* * What's the offset? */ if (p->k >= SLL_HDR_LEN) { /* * It's within the link-layer payload; that starts at an * offset of 0, as far as the kernel packet filter is * concerned, so subtract the length of the link-layer * header. */ p->k -= SLL_HDR_LEN; } else if (p->k == 14) { /* * It's the protocol field; map it to the special magic * kernel offset for that field. */ p->k = SKF_AD_OFF + SKF_AD_PROTOCOL; } else { /* * It's within the header, but it's not one of those * fields; we can't do that in the kernel, so punt * to userland. */ return -1; } return 0; } static int set_kernel_filter(pcap_t *handle, struct sock_fprog *fcode) { int total_filter_on = 0; int save_mode; int ret; int save_errno; /* * The socket filter code doesn't discard all packets queued * up on the socket when the filter is changed; this means * that packets that don't match the new filter may show up * after the new filter is put onto the socket, if those * packets haven't yet been read. * * This means, for example, that if you do a tcpdump capture * with a filter, the first few packets in the capture might * be packets that wouldn't have passed the filter. * * We therefore discard all packets queued up on the socket * when setting a kernel filter. (This isn't an issue for * userland filters, as the userland filtering is done after * packets are queued up.) * * To flush those packets, we put the socket in read-only mode, * and read packets from the socket until there are no more to * read. * * In order to keep that from being an infinite loop - i.e., * to keep more packets from arriving while we're draining * the queue - we put the "total filter", which is a filter * that rejects all packets, onto the socket before draining * the queue. * * This code deliberately ignores any errors, so that you may * get bogus packets if an error occurs, rather than having * the filtering done in userland even if it could have been * done in the kernel. */ if (setsockopt(handle->fd, SOL_SOCKET, SO_ATTACH_FILTER, &total_fcode, sizeof(total_fcode)) == 0) { char drain[1]; /* * Note that we've put the total filter onto the socket. */ total_filter_on = 1; /* * Save the socket's current mode, and put it in * non-blocking mode; we drain it by reading packets * until we get an error (which is normally a * "nothing more to be read" error). */ save_mode = fcntl(handle->fd, F_GETFL, 0); if (save_mode != -1 && fcntl(handle->fd, F_SETFL, save_mode | O_NONBLOCK) >= 0) { while (recv(handle->fd, &drain, sizeof drain, MSG_TRUNC) >= 0) ; save_errno = errno; fcntl(handle->fd, F_SETFL, save_mode); if (save_errno != EAGAIN) { /* Fatal error */ reset_kernel_filter(handle); snprintf(handle->errbuf, sizeof(handle->errbuf), "recv: %s", pcap_strerror(save_errno)); return -2; } } } /* * Now attach the new filter. */ ret = setsockopt(handle->fd, SOL_SOCKET, SO_ATTACH_FILTER, fcode, sizeof(*fcode)); if (ret == -1 && total_filter_on) { /* * Well, we couldn't set that filter on the socket, * but we could set the total filter on the socket. * * This could, for example, mean that the filter was * too big to put into the kernel, so we'll have to * filter in userland; in any case, we'll be doing * filtering in userland, so we need to remove the * total filter so we see packets. */ save_errno = errno; /* * XXX - if this fails, we're really screwed; * we have the total filter on the socket, * and it won't come off. What do we do then? */ reset_kernel_filter(handle); errno = save_errno; } return ret; } static int reset_kernel_filter(pcap_t *handle) { /* setsockopt() barfs unless it get a dummy parameter */ int dummy; return setsockopt(handle->fd, SOL_SOCKET, SO_DETACH_FILTER, &dummy, sizeof(dummy)); } #endif