Commit message: wireless: radiotap: fix parsing buffer overrun

When parsing an invalid radiotap header, the parser can overrun
the buffer that is passed in because it doesn't correctly check
 1) the minimum radiotap header size
 2) the space for extended bitmaps

The first issue doesn't affect any in-kernel user as they all
check the minimum size before calling the radiotap function.
The second issue could potentially affect the kernel if an skb
is passed in that consists only of the radiotap header with a
lot of extended bitmaps that extend past the SKB. In that case
a read-only buffer overrun by at most 4 bytes is possible.

Fix this by adding the appropriate checks to the parser.

Cc: stable@vger.kernel.org
Reported-by: Evan Huus <eapache@gmail.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
CVE: CVE-2013-7027
CWE: CWE-119
Vulnerability description: The ieee80211_radiotap_iterator_init function in net/wireless/radiotap.c in the Linux kernel before 3.11.7 does not check whether a frame contains any data outside of the header, which might allow attackers to cause a denial of service (buffer over-read) via a crafted header.

Project: linux
File: radiotap.c

static void find_ns(struct ieee80211_radiotap_iterator *iterator,
		    uint32_t oui, uint8_t subns)
{
	int i;

	iterator->current_namespace = NULL;

	if (!iterator->_vns)
		return;

	for (i = 0; i < iterator->_vns->n_ns; i++) {
		if (iterator->_vns->ns[i].oui != oui)
			continue;
		if (iterator->_vns->ns[i].subns != subns)
			continue;

		iterator->current_namespace = &iterator->_vns->ns[i];
		break;
	}
}

Project: linux
File: radiotap.c

int ieee80211_radiotap_iterator_next(
	struct ieee80211_radiotap_iterator *iterator)
{
	while (1) {
		int hit = 0;
		int pad, align, size, subns;
		uint32_t oui;

		/* if no more EXT bits, that's it */
		if ((iterator->_arg_index % 32) == IEEE80211_RADIOTAP_EXT &&
		    !(iterator->_bitmap_shifter & 1))
			return -ENOENT;

		if (!(iterator->_bitmap_shifter & 1))
			goto next_entry; /* arg not present */

		/* get alignment/size of data */
		switch (iterator->_arg_index % 32) {
		case IEEE80211_RADIOTAP_RADIOTAP_NAMESPACE:
		case IEEE80211_RADIOTAP_EXT:
			align = 1;
			size = 0;
			break;
		case IEEE80211_RADIOTAP_VENDOR_NAMESPACE:
			align = 2;
			size = 6;
			break;
		default:
			if (!iterator->current_namespace ||
			    iterator->_arg_index >= iterator->current_namespace->n_bits) {
				if (iterator->current_namespace == &radiotap_ns)
					return -ENOENT;
				align = 0;
			} else {
				align = iterator->current_namespace->align_size[iterator->_arg_index].align;
				size = iterator->current_namespace->align_size[iterator->_arg_index].size;
			}
			if (!align) {
				/* skip all subsequent data */
				iterator->_arg = iterator->_next_ns_data;
				/* give up on this namespace */
				iterator->current_namespace = NULL;
				goto next_entry;
			}
			break;
		}

		/*
		 * arg is present, account for alignment padding
		 *
		 * Note that 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 = ((unsigned long)iterator->_arg -
		       (unsigned long)iterator->_rtheader) & (align - 1);

		if (pad)
			iterator->_arg += align - pad;

		if (iterator->_arg_index % 32 == IEEE80211_RADIOTAP_VENDOR_NAMESPACE) {
			int vnslen;

			if ((unsigned long)iterator->_arg + size -
			    (unsigned long)iterator->_rtheader >
			    (unsigned long)iterator->_max_length)
				return -EINVAL;

			oui = (*iterator->_arg << 16) |
				(*(iterator->_arg + 1) << 8) |
				*(iterator->_arg + 2);
			subns = *(iterator->_arg + 3);

			find_ns(iterator, oui, subns);

			vnslen = get_unaligned_le16(iterator->_arg + 4);
			iterator->_next_ns_data = iterator->_arg + size + vnslen;
			if (!iterator->current_namespace)
				size += vnslen;
		}

		/*
		 * 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;
		iterator->this_arg_size = size;

		/* internally move on the size of this arg */
		iterator->_arg += size;

		/*
		 * 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 ((unsigned long)iterator->_arg -
		    (unsigned long)iterator->_rtheader >
		    (unsigned long)iterator->_max_length)
			return -EINVAL;

		/* these special ones are valid in each bitmap word */
		switch (iterator->_arg_index % 32) {
		case IEEE80211_RADIOTAP_VENDOR_NAMESPACE:
			iterator->_reset_on_ext = 1;

			iterator->is_radiotap_ns = 0;
			/*
			 * If parser didn't register this vendor
			 * namespace with us, allow it to show it
			 * as 'raw. Do do that, set argument index
			 * to vendor namespace.
			 */
			iterator->this_arg_index =
				IEEE80211_RADIOTAP_VENDOR_NAMESPACE;
			if (!iterator->current_namespace)
				hit = 1;
			goto next_entry;
		case IEEE80211_RADIOTAP_RADIOTAP_NAMESPACE:
			iterator->_reset_on_ext = 1;
			iterator->current_namespace = &radiotap_ns;
			iterator->is_radiotap_ns = 1;
			goto next_entry;
		case IEEE80211_RADIOTAP_EXT:
			/*
			 * bit 31 was set, there is more
			 * -- move to next u32 bitmap
			 */
			iterator->_bitmap_shifter =
				get_unaligned_le32(iterator->_next_bitmap);
			iterator->_next_bitmap++;
			if (iterator->_reset_on_ext)
				iterator->_arg_index = 0;
			else
				iterator->_arg_index++;
			iterator->_reset_on_ext = 0;
			break;
		default:
			/* we've got a hit! */
			hit = 1;
 next_entry:
			iterator->_bitmap_shifter >>= 1;
			iterator->_arg_index++;
		}

		/* if we found a valid arg earlier, return it now */
		if (hit)
			return 0;
	}
}