diff options
Diffstat (limited to 'net/wireless/radiotap.c')
| -rw-r--r-- | net/wireless/radiotap.c | 257 |
1 files changed, 257 insertions, 0 deletions
diff --git a/net/wireless/radiotap.c b/net/wireless/radiotap.c new file mode 100644 index 0000000..68c11d0 --- /dev/null +++ b/net/wireless/radiotap.c @@ -0,0 +1,257 @@ +/* + * Radiotap parser + * + * Copyright 2007 Andy Green <andy@warmcat.com> + */ + +#include <net/cfg80211.h> +#include <net/ieee80211_radiotap.h> +#include <asm/unaligned.h> + +/* 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 < le16_to_cpu(get_unaligned(&radiotap_header->it_len))) + return -EINVAL; + + iterator->rtheader = radiotap_header; + iterator->max_length = le16_to_cpu(get_unaligned( + &radiotap_header->it_len)); + iterator->arg_index = 0; + iterator->bitmap_shifter = le32_to_cpu(get_unaligned( + &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<<IEEE80211_RADIOTAP_EXT))) { + while (le32_to_cpu(get_unaligned((__le32 *)iterator->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 + /* + * 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 = le32_to_cpu( + get_unaligned(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); |
