/* * INET An implementation of the TCP/IP protocol suite for the LINUX * operating system. INET is implemented using the BSD Socket * interface as the means of communication with the user level. * * The IP fragmentation functionality. * * Version: $Id: ip_fragment.c,v 1.59 2002/01/12 07:54:56 davem Exp $ * * Authors: Fred N. van Kempen <waltje@uWalt.NL.Mugnet.ORG> * Alan Cox <Alan.Cox@linux.org> * * Fixes: * Alan Cox : Split from ip.c , see ip_input.c for history. * David S. Miller : Begin massive cleanup... * Andi Kleen : Add sysctls. * xxxx : Overlapfrag bug. * Ultima : ip_expire() kernel panic. * Bill Hawes : Frag accounting and evictor fixes. * John McDonald : 0 length frag bug. * Alexey Kuznetsov: SMP races, threading, cleanup. * Patrick McHardy : LRU queue of frag heads for evictor. */ #include <linux/compiler.h> #include <linux/module.h> #include <linux/types.h> #include <linux/mm.h> #include <linux/jiffies.h> #include <linux/skbuff.h> #include <linux/list.h> #include <linux/ip.h> #include <linux/icmp.h> #include <linux/netdevice.h> #include <linux/jhash.h> #include <linux/random.h> #include <net/sock.h> #include <net/ip.h> #include <net/icmp.h> #include <net/checksum.h> #include <net/inetpeer.h> #include <linux/tcp.h> #include <linux/udp.h> #include <linux/inet.h> #include <linux/netfilter_ipv4.h> /* NOTE. Logic of IP defragmentation is parallel to corresponding IPv6 * code now. If you change something here, _PLEASE_ update ipv6/reassembly.c * as well. Or notify me, at least. --ANK */ /* Fragment cache limits. We will commit 256K at one time. Should we * cross that limit we will prune down to 192K. This should cope with * even the most extreme cases without allowing an attacker to measurably * harm machine performance. */ int sysctl_ipfrag_high_thresh __read_mostly = 256*1024; int sysctl_ipfrag_low_thresh __read_mostly = 192*1024; int sysctl_ipfrag_max_dist __read_mostly = 64; /* Important NOTE! Fragment queue must be destroyed before MSL expires. * RFC791 is wrong proposing to prolongate timer each fragment arrival by TTL. */ int sysctl_ipfrag_time __read_mostly = IP_FRAG_TIME; struct ipfrag_skb_cb { struct inet_skb_parm h; int offset; }; #define FRAG_CB(skb) ((struct ipfrag_skb_cb*)((skb)->cb)) /* Describe an entry in the "incomplete datagrams" queue. */ struct ipq { struct hlist_node list; struct list_head lru_list; /* lru list member */ u32 user; __be32 saddr; __be32 daddr; __be16 id; u8 protocol; u8 last_in; #define COMPLETE 4 #define FIRST_IN 2 #define LAST_IN 1 struct sk_buff *fragments; /* linked list of received fragments */ int len; /* total length of original datagram */ int meat; spinlock_t lock; atomic_t refcnt; struct timer_list timer; /* when will this queue expire? */ ktime_t stamp; int iif; unsigned int rid; struct inet_peer *peer; }; /* Hash table. */ #define IPQ_HASHSZ 64 /* Per-bucket lock is easy to add now. */ static struct hlist_head ipq_hash[IPQ_HASHSZ]; static DEFINE_RWLOCK(ipfrag_lock); static u32 ipfrag_hash_rnd; static LIST_HEAD(ipq_lru_list); int ip_frag_nqueues = 0; static __inline__ void __ipq_unlink(struct ipq *qp) { hlist_del(&qp->list); list_del(&qp->lru_list); ip_frag_nqueues--; } static __inline__ void ipq_unlink(struct ipq *ipq) { write_lock(&ipfrag_lock); __ipq_unlink(ipq); write_unlock(&ipfrag_lock); } static unsigned int ipqhashfn(__be16 id, __be32 saddr, __be32 daddr, u8 prot) { return jhash_3words((__force u32)id << 16 | prot, (__force u32)saddr, (__force u32)daddr, ipfrag_hash_rnd) & (IPQ_HASHSZ - 1); } static struct timer_list ipfrag_secret_timer; int sysctl_ipfrag_secret_interval __read_mostly = 10 * 60 * HZ; static void ipfrag_secret_rebuild(unsigned long dummy) { unsigned long now = jiffies; int i; write_lock(&ipfrag_lock); get_random_bytes(&ipfrag_hash_rnd, sizeof(u32)); for (i = 0; i < IPQ_HASHSZ; i++) { struct ipq *q; struct hlist_node *p, *n; hlist_for_each_entry_safe(q, p, n, &ipq_hash[i], list) { unsigned int hval = ipqhashfn(q->id, q->saddr, q->daddr, q->protocol); if (hval != i) { hlist_del(&q->list); /* Relink to new hash chain. */ hlist_add_head(&q->list, &ipq_hash[hval]); } } } write_unlock(&ipfrag_lock); mod_timer(&ipfrag_secret_timer, now + sysctl_ipfrag_secret_interval); } atomic_t ip_frag_mem = ATOMIC_INIT(0); /* Memory used for fragments */ /* Memory Tracking Functions. */ static __inline__ void frag_kfree_skb(struct sk_buff *skb, int *work) { if (work) *work -= skb->truesize; atomic_sub(skb->truesize, &ip_frag_mem); kfree_skb(skb); } static __inline__ void frag_free_queue(struct ipq *qp, int *work) { if (work) *work -= sizeof(struct ipq); atomic_sub(sizeof(struct ipq), &ip_frag_mem); kfree(qp); } static __inline__ struct ipq *frag_alloc_queue(void) { struct ipq *qp = kmalloc(sizeof(struct ipq), GFP_ATOMIC); if (!qp) return NULL; atomic_add(sizeof(struct ipq), &ip_frag_mem); return qp; } /* Destruction primitives. */ /* Complete destruction of ipq. */ static void ip_frag_destroy(struct ipq *qp, int *work) { struct sk_buff *fp; BUG_TRAP(qp->last_in&COMPLETE); BUG_TRAP(del_timer(&qp->timer) == 0); if (qp->peer) inet_putpeer(qp->peer); /* Release all fragment data. */ fp = qp->fragments; while (fp) { struct sk_buff *xp = fp->next; frag_kfree_skb(fp, work); fp = xp; } /* Finally, release the queue descriptor itself. */ frag_free_queue(qp, work); } static __inline__ void ipq_put(struct ipq *ipq, int *work) { if (atomic_dec_and_test(&ipq->refcnt)) ip_frag_destroy(ipq, work); } /* Kill ipq entry. It is not destroyed immediately, * because caller (and someone more) holds reference count. */ static void ipq_kill(struct ipq *ipq) { if (del_timer(&ipq->timer)) atomic_dec(&ipq->refcnt); if (!(ipq->last_in & COMPLETE)) { ipq_unlink(ipq); atomic_dec(&ipq->refcnt); ipq->last_in |= COMPLETE; } } /* Memory limiting on fragments. Evictor trashes the oldest * fragment queue until we are back under the threshold. */ static void ip_evictor(void) { struct ipq *qp; struct list_head *tmp; int work; work = atomic_read(&ip_frag_mem) - sysctl_ipfrag_low_thresh; if (work <= 0) return; while (work > 0) { read_lock(&ipfrag_lock); if (list_empty(&ipq_lru_list)) { read_unlock(&ipfrag_lock); return; } tmp = ipq_lru_list.next; qp = list_entry(tmp, struct ipq, lru_list); atomic_inc(&qp->refcnt); read_unlock(&ipfrag_lock); spin_lock(&qp->lock); if (!(qp->last_in&COMPLETE)) ipq_kill(qp); spin_unlock(&qp->lock); ipq_put(qp, &work); IP_INC_STATS_BH(IPSTATS_MIB_REASMFAILS); } } /* * Oops, a fragment queue timed out. Kill it and send an ICMP reply. */ static void ip_expire(unsigned long arg) { struct ipq *qp = (struct ipq *) arg; spin_lock(&qp->lock); if (qp->last_in & COMPLETE) goto out; ipq_kill(qp); IP_INC_STATS_BH(IPSTATS_MIB_REASMTIMEOUT); IP_INC_STATS_BH(IPSTATS_MIB_REASMFAILS); if ((qp->last_in&FIRST_IN) && qp->fragments != NULL) { struct sk_buff *head = qp->fragments; /* Send an ICMP "Fragment Reassembly Timeout" message. */ if ((head->dev = dev_get_by_index(qp->iif)) != NULL) { icmp_send(head, ICMP_TIME_EXCEEDED, ICMP_EXC_FRAGTIME, 0); dev_put(head->dev); } } out: spin_unlock(&qp->lock); ipq_put(qp, NULL); } /* Creation primitives. */ static struct ipq *ip_frag_intern(struct ipq *qp_in) { struct ipq *qp; #ifdef CONFIG_SMP struct hlist_node *n; #endif unsigned int hash; write_lock(&ipfrag_lock); hash = ipqhashfn(qp_in->id, qp_in->saddr, qp_in->daddr, qp_in->protocol); #ifdef CONFIG_SMP /* With SMP race we have to recheck hash table, because * such entry could be created on other cpu, while we * promoted read lock to write lock. */ hlist_for_each_entry(qp, n, &ipq_hash[hash], list) { if (qp->id == qp_in->id && qp->saddr == qp_in->saddr && qp->daddr == qp_in->daddr && qp->protocol == qp_in->protocol && qp->user == qp_in->user) { atomic_inc(&qp->refcnt); write_unlock(&ipfrag_lock); qp_in->last_in |= COMPLETE; ipq_put(qp_in, NULL); return qp; } } #endif qp = qp_in; if (!mod_timer(&qp->timer, jiffies + sysctl_ipfrag_time)) atomic_inc(&qp->refcnt); atomic_inc(&qp->refcnt); hlist_add_head(&qp->list, &ipq_hash[hash]); INIT_LIST_HEAD(&qp->lru_list); list_add_tail(&qp->lru_list, &ipq_lru_list); ip_frag_nqueues++; write_unlock(&ipfrag_lock); return qp; } /* Add an entry to the 'ipq' queue for a newly received IP datagram. */ static struct ipq *ip_frag_create(struct iphdr *iph, u32 user) { struct ipq *qp; if ((qp = frag_alloc_queue()) == NULL) goto out_nomem; qp->protocol = iph->protocol; qp->last_in = 0; qp->id = iph->id; qp->saddr = iph->saddr; qp->daddr = iph->daddr; qp->user = user; qp->len = 0; qp->meat = 0; qp->fragments = NULL; qp->iif = 0; qp->peer = sysctl_ipfrag_max_dist ? inet_getpeer(iph->saddr, 1) : NULL; /* Initialize a timer for this entry. */ init_timer(&qp->timer); qp->timer.data = (unsigned long) qp; /* pointer to queue */ qp->timer.function = ip_expire; /* expire function */ spin_lock_init(&qp->lock); atomic_set(&qp->refcnt, 1); return ip_frag_intern(qp); out_nomem: LIMIT_NETDEBUG(KERN_ERR "ip_frag_create: no memory left !\n"); return NULL; } /* Find the correct entry in the "incomplete datagrams" queue for * this IP datagram, and create new one, if nothing is found. */ static inline struct ipq *ip_find(struct iphdr *iph, u32 user) { __be16 id = iph->id; __be32 saddr = iph->saddr; __be32 daddr = iph->daddr; __u8 protocol = iph->protocol; unsigned int hash; struct ipq *qp; struct hlist_node *n; read_lock(&ipfrag_lock); hash = ipqhashfn(id, saddr, daddr, protocol); hlist_for_each_entry(qp, n, &ipq_hash[hash], list) { if (qp->id == id && qp->saddr == saddr && qp->daddr == daddr && qp->protocol == protocol && qp->user == user) { atomic_inc(&qp->refcnt); read_unlock(&ipfrag_lock); return qp; } } read_unlock(&ipfrag_lock); return ip_frag_create(iph, user); } /* Is the fragment too far ahead to be part of ipq? */ static inline int ip_frag_too_far(struct ipq *qp) { struct inet_peer *peer = qp->peer; unsigned int max = sysctl_ipfrag_max_dist; unsigned int start, end; int rc; if (!peer || !max) return 0; start = qp->rid; end = atomic_inc_return(&peer->rid); qp->rid = end; rc = qp->fragments && (end - start) > max; if (rc) { IP_INC_STATS_BH(IPSTATS_MIB_REASMFAILS); } return rc; } static int ip_frag_reinit(struct ipq *qp) { struct sk_buff *fp; if (!mod_timer(&qp->timer, jiffies + sysctl_ipfrag_time)) { atomic_inc(&qp->refcnt); return -ETIMEDOUT; } fp = qp->fragments; do { struct sk_buff *xp = fp->next; frag_kfree_skb(fp, NULL); fp = xp; } while (fp); qp->last_in = 0; qp->len = 0; qp->meat = 0; qp->fragments = NULL; qp->iif = 0; return 0; } /* Add new segment to existing queue. */ static void ip_frag_queue(struct ipq *qp, struct sk_buff *skb) { struct sk_buff *prev, *next; int flags, offset; int ihl, end; if (qp->last_in & COMPLETE) goto err; if (!(IPCB(skb)->flags & IPSKB_FRAG_COMPLETE) && unlikely(ip_frag_too_far(qp)) && unlikely(ip_frag_reinit(qp))) { ipq_kill(qp); goto err; } offset = ntohs(ip_hdr(skb)->frag_off); flags = offset & ~IP_OFFSET; offset &= IP_OFFSET; offset <<= 3; /* offset is in 8-byte chunks */ ihl = ip_hdrlen(skb); /* Determine the position of this fragment. */ end = offset + skb->len - ihl; /* Is this the final fragment? */ if ((flags & IP_MF) == 0) { /* If we already have some bits beyond end * or have different end, the segment is corrrupted. */ if (end < qp->len || ((qp->last_in & LAST_IN) && end != qp->len)) goto err; qp->last_in |= LAST_IN; qp->len = end; } else { if (end&7) { end &= ~7; if (skb->ip_summed != CHECKSUM_UNNECESSARY) skb->ip_summed = CHECKSUM_NONE; } if (end > qp->len) { /* Some bits beyond end -> corruption. */ if (qp->last_in & LAST_IN) goto err; qp->len = end; } } if (end == offset) goto err; if (pskb_pull(skb, ihl) == NULL) goto err; if (pskb_trim_rcsum(skb, end-offset)) goto err; /* Find out which fragments are in front and at the back of us * in the chain of fragments so far. We must know where to put * this fragment, right? */ prev = NULL; for (next = qp->fragments; next != NULL; next = next->next) { if (FRAG_CB(next)->offset >= offset) break; /* bingo! */ prev = next; } /* We found where to put this one. Check for overlap with * preceding fragment, and, if needed, align things so that * any overlaps are eliminated. */ if (prev) { int i = (FRAG_CB(prev)->offset + prev->len) - offset; if (i > 0) { offset += i; if (end <= offset) goto err; if (!pskb_pull(skb, i)) goto err; if (skb->ip_summed != CHECKSUM_UNNECESSARY) skb->ip_summed = CHECKSUM_NONE; } } while (next && FRAG_CB(next)->offset < end) { int i = end - FRAG_CB(next)->offset; /* overlap is 'i' bytes */ if (i < next->len) { /* Eat head of the next overlapped fragment * and leave the loop. The next ones cannot overlap. */ if (!pskb_pull(next, i)) goto err; FRAG_CB(next)->offset += i; qp->meat -= i; if (next->ip_summed != CHECKSUM_UNNECESSARY) next->ip_summed = CHECKSUM_NONE; break; } else { struct sk_buff *free_it = next; /* Old fragment is completely overridden with * new one drop it. */ next = next->next; if (prev) prev->next = next; else qp->fragments = next; qp->meat -= free_it->len; frag_kfree_skb(free_it, NULL); } } FRAG_CB(skb)->offset = offset; /* Insert this fragment in the chain of fragments. */ skb->next = next; if (prev) prev->next = skb; else qp->fragments = skb; if (skb->dev) qp->iif = skb->dev->ifindex; skb->dev = NULL; qp->stamp = skb->tstamp; qp->meat += skb->len; atomic_add(skb->truesize, &ip_frag_mem); if (offset == 0) qp->last_in |= FIRST_IN; write_lock(&ipfrag_lock); list_move_tail(&qp->lru_list, &ipq_lru_list); write_unlock(&ipfrag_lock); return; err: kfree_skb(skb); } /* Build a new IP datagram from all its fragments. */ static struct sk_buff *ip_frag_reasm(struct ipq *qp, struct net_device *dev) { struct iphdr *iph; struct sk_buff *fp, *head = qp->fragments; int len; int ihlen; ipq_kill(qp); BUG_TRAP(head != NULL); BUG_TRAP(FRAG_CB(head)->offset == 0); /* Allocate a new buffer for the datagram. */ ihlen = ip_hdrlen(head); len = ihlen + qp->len; if (len > 65535) goto out_oversize; /* Head of list must not be cloned. */ if (skb_cloned(head) && pskb_expand_head(head, 0, 0, GFP_ATOMIC)) goto out_nomem; /* If the first fragment is fragmented itself, we split * it to two chunks: the first with data and paged part * and the second, holding only fragments. */ if (skb_shinfo(head)->frag_list) { struct sk_buff *clone; int i, plen = 0; if ((clone = alloc_skb(0, GFP_ATOMIC)) == NULL) goto out_nomem; clone->next = head->next; head->next = clone; skb_shinfo(clone)->frag_list = skb_shinfo(head)->frag_list; skb_shinfo(head)->frag_list = NULL; for (i=0; i<skb_shinfo(head)->nr_frags; i++) plen += skb_shinfo(head)->frags[i].size; clone->len = clone->data_len = head->data_len - plen; head->data_len -= clone->len; head->len -= clone->len; clone->csum = 0; clone->ip_summed = head->ip_summed; atomic_add(clone->truesize, &ip_frag_mem); } skb_shinfo(head)->frag_list = head->next; skb_push(head, head->data - skb_network_header(head)); atomic_sub(head->truesize, &ip_frag_mem); for (fp=head->next; fp; fp = fp->next) { head->data_len += fp->len; head->len += fp->len; if (head->ip_summed != fp->ip_summed) head->ip_summed = CHECKSUM_NONE; else if (head->ip_summed == CHECKSUM_COMPLETE) head->csum = csum_add(head->csum, fp->csum); head->truesize += fp->truesize; atomic_sub(fp->truesize, &ip_frag_mem); } head->next = NULL; head->dev = dev; head->tstamp = qp->stamp; iph = ip_hdr(head); iph->frag_off = 0; iph->tot_len = htons(len); IP_INC_STATS_BH(IPSTATS_MIB_REASMOKS); qp->fragments = NULL; return head; out_nomem: LIMIT_NETDEBUG(KERN_ERR "IP: queue_glue: no memory for gluing " "queue %p\n", qp); goto out_fail; out_oversize: if (net_ratelimit()) printk(KERN_INFO "Oversized IP packet from %d.%d.%d.%d.\n", NIPQUAD(qp->saddr)); out_fail: IP_INC_STATS_BH(IPSTATS_MIB_REASMFAILS); return NULL; } /* Process an incoming IP datagram fragment. */ struct sk_buff *ip_defrag(struct sk_buff *skb, u32 user) { struct ipq *qp; struct net_device *dev; IP_INC_STATS_BH(IPSTATS_MIB_REASMREQDS); /* Start by cleaning up the memory. */ if (atomic_read(&ip_frag_mem) > sysctl_ipfrag_high_thresh) ip_evictor(); dev = skb->dev; /* Lookup (or create) queue header */ if ((qp = ip_find(ip_hdr(skb), user)) != NULL) { struct sk_buff *ret = NULL; spin_lock(&qp->lock); ip_frag_queue(qp, skb); if (qp->last_in == (FIRST_IN|LAST_IN) && qp->meat == qp->len) ret = ip_frag_reasm(qp, dev); spin_unlock(&qp->lock); ipq_put(qp, NULL); return ret; } IP_INC_STATS_BH(IPSTATS_MIB_REASMFAILS); kfree_skb(skb); return NULL; } void __init ipfrag_init(void) { ipfrag_hash_rnd = (u32) ((num_physpages ^ (num_physpages>>7)) ^ (jiffies ^ (jiffies >> 6))); init_timer(&ipfrag_secret_timer); ipfrag_secret_timer.function = ipfrag_secret_rebuild; ipfrag_secret_timer.expires = jiffies + sysctl_ipfrag_secret_interval; add_timer(&ipfrag_secret_timer); } EXPORT_SYMBOL(ip_defrag);