/* * Radiotap parser * * Copyright 2007 Andy Green */ #include #include #include /* function prototypes and related defs are in include/net/cfg80211.h */ /** * ieee80211_radiotap_iterator_init - radiotap parser iterator initialization * @iterator: radiotap_iterator to initialize * @radiotap_header: radiotap header to parse * @max_length: total length we can parse into (eg, whole packet length) * * Returns: 0 or a negative error code if there is a problem. * * This function initializes an opaque iterator struct which can then * be passed to ieee80211_radiotap_iterator_next() to visit every radiotap * argument which is present in the header. It knows about extended * present headers and handles them. * * How to use: * call __ieee80211_radiotap_iterator_init() to init a semi-opaque iterator * struct ieee80211_radiotap_iterator (no need to init the struct beforehand) * checking for a good 0 return code. Then loop calling * __ieee80211_radiotap_iterator_next()... it returns either 0, * -ENOENT if there are no more args to parse, or -EINVAL if there is a problem. * The iterator's @this_arg member points to the start of the argument * associated with the current argument index that is present, which can be * found in the iterator's @this_arg_index member. This arg index corresponds * to the IEEE80211_RADIOTAP_... defines. * * Radiotap header length: * You can find the CPU-endian total radiotap header length in * iterator->max_length after executing ieee80211_radiotap_iterator_init() * successfully. * * Alignment Gotcha: * You must take care when dereferencing iterator.this_arg * for multibyte types... the pointer is not aligned. Use * get_unaligned((type *)iterator.this_arg) to dereference * iterator.this_arg for type "type" safely on all arches. * * Example code: * See Documentation/networking/radiotap-headers.txt */ int ieee80211_radiotap_iterator_init( struct ieee80211_radiotap_iterator *iterator, struct ieee80211_radiotap_header *radiotap_header, int max_length) { /* Linux only supports version 0 radiotap format */ if (radiotap_header->it_version) return -EINVAL; /* sanity check for allowed length and radiotap length field */ if (max_length < get_unaligned_le16(&radiotap_header->it_len)) return -EINVAL; iterator->rtheader = radiotap_header; iterator->max_length = get_unaligned_le16(&radiotap_header->it_len); iterator->arg_index = 0; iterator->bitmap_shifter = get_unaligned_le32(&radiotap_header->it_present); iterator->arg = (u8 *)radiotap_header + sizeof(*radiotap_header); iterator->this_arg = NULL; /* find payload start allowing for extended bitmap(s) */ if (unlikely(iterator->bitmap_shifter & (1<arg) & (1 << IEEE80211_RADIOTAP_EXT)) { iterator->arg += sizeof(u32); /* * check for insanity where the present bitmaps * keep claiming to extend up to or even beyond the * stated radiotap header length */ if (((ulong)iterator->arg - (ulong)iterator->rtheader) > iterator->max_length) return -EINVAL; } iterator->arg += sizeof(u32); /* * no need to check again for blowing past stated radiotap * header length, because ieee80211_radiotap_iterator_next * checks it before it is dereferenced */ } /* we are all initialized happily */ return 0; } EXPORT_SYMBOL(ieee80211_radiotap_iterator_init); /** * ieee80211_radiotap_iterator_next - return next radiotap parser iterator arg * @iterator: radiotap_iterator to move to next arg (if any) * * Returns: 0 if there is an argument to handle, * -ENOENT if there are no more args or -EINVAL * if there is something else wrong. * * This function provides the next radiotap arg index (IEEE80211_RADIOTAP_*) * in @this_arg_index and sets @this_arg to point to the * payload for the field. It takes care of alignment handling and extended * present fields. @this_arg can be changed by the caller (eg, * incremented to move inside a compound argument like * IEEE80211_RADIOTAP_CHANNEL). The args pointed to are in * little-endian format whatever the endianess of your CPU. * * Alignment Gotcha: * You must take care when dereferencing iterator.this_arg * for multibyte types... the pointer is not aligned. Use * get_unaligned((type *)iterator.this_arg) to dereference * iterator.this_arg for type "type" safely on all arches. */ int ieee80211_radiotap_iterator_next( struct ieee80211_radiotap_iterator *iterator) { /* * small length lookup table for all radiotap types we heard of * starting from b0 in the bitmap, so we can walk the payload * area of the radiotap header * * There is a requirement to pad args, so that args * of a given length must begin at a boundary of that length * -- but note that compound args are allowed (eg, 2 x u16 * for IEEE80211_RADIOTAP_CHANNEL) so total arg length is not * a reliable indicator of alignment requirement. * * upper nybble: content alignment for arg * lower nybble: content length for arg */ static const u8 rt_sizes[] = { [IEEE80211_RADIOTAP_TSFT] = 0x88, [IEEE80211_RADIOTAP_FLAGS] = 0x11, [IEEE80211_RADIOTAP_RATE] = 0x11, [IEEE80211_RADIOTAP_CHANNEL] = 0x24, [IEEE80211_RADIOTAP_FHSS] = 0x22, [IEEE80211_RADIOTAP_DBM_ANTSIGNAL] = 0x11, [IEEE80211_RADIOTAP_DBM_ANTNOISE] = 0x11, [IEEE80211_RADIOTAP_LOCK_QUALITY] = 0x22, [IEEE80211_RADIOTAP_TX_ATTENUATION] = 0x22, [IEEE80211_RADIOTAP_DB_TX_ATTENUATION] = 0x22, [IEEE80211_RADIOTAP_DBM_TX_POWER] = 0x11, [IEEE80211_RADIOTAP_ANTENNA] = 0x11, [IEEE80211_RADIOTAP_DB_ANTSIGNAL] = 0x11, [IEEE80211_RADIOTAP_DB_ANTNOISE] = 0x11, [IEEE80211_RADIOTAP_RX_FLAGS] = 0x22, [IEEE80211_RADIOTAP_TX_FLAGS] = 0x22, [IEEE80211_RADIOTAP_RTS_RETRIES] = 0x11, [IEEE80211_RADIOTAP_DATA_RETRIES] = 0x11, /* * add more here as they are defined in * include/net/ieee80211_radiotap.h */ }; /* * for every radiotap entry we can at * least skip (by knowing the length)... */ while (iterator->arg_index < sizeof(rt_sizes)) { int hit = 0; int pad; if (!(iterator->bitmap_shifter & 1)) goto next_entry; /* arg not present */ /* * arg is present, account for alignment padding * 8-bit args can be at any alignment * 16-bit args must start on 16-bit boundary * 32-bit args must start on 32-bit boundary * 64-bit args must start on 64-bit boundary * * note that total arg size can differ from alignment of * elements inside arg, so we use upper nybble of length * table to base alignment on * * also note: these alignments are ** relative to the * start of the radiotap header **. There is no guarantee * that the radiotap header itself is aligned on any * kind of boundary. * * the above is why get_unaligned() is used to dereference * multibyte elements from the radiotap area */ pad = (((ulong)iterator->arg) - ((ulong)iterator->rtheader)) & ((rt_sizes[iterator->arg_index] >> 4) - 1); if (pad) iterator->arg += (rt_sizes[iterator->arg_index] >> 4) - pad; /* * this is what we will return to user, but we need to * move on first so next call has something fresh to test */ iterator->this_arg_index = iterator->arg_index; iterator->this_arg = iterator->arg; hit = 1; /* internally move on the size of this arg */ iterator->arg += rt_sizes[iterator->arg_index] & 0x0f; /* * check for insanity where we are given a bitmap that * claims to have more arg content than the length of the * radiotap section. We will normally end up equalling this * max_length on the last arg, never exceeding it. */ if (((ulong)iterator->arg - (ulong)iterator->rtheader) > iterator->max_length) return -EINVAL; next_entry: iterator->arg_index++; if (unlikely((iterator->arg_index & 31) == 0)) { /* completed current u32 bitmap */ if (iterator->bitmap_shifter & 1) { /* b31 was set, there is more */ /* move to next u32 bitmap */ iterator->bitmap_shifter = get_unaligned_le32(iterator->next_bitmap); iterator->next_bitmap++; } else /* no more bitmaps: end */ iterator->arg_index = sizeof(rt_sizes); } else /* just try the next bit */ iterator->bitmap_shifter >>= 1; /* if we found a valid arg earlier, return it now */ if (hit) return 0; } /* we don't know how to handle any more args, we're done */ return -ENOENT; } EXPORT_SYMBOL(ieee80211_radiotap_iterator_next);