CVE-2026-80800: nfc: llcp: bound the connect_sn TLV walk to the skb

CVE-2026-80800: nfc: llcp: bound the connect_sn TLV walk to the skb

[Greg Kroah-Hartman]

From: Greg Kroah-Hartman <gregkh@kernel.org>

Description
===========

In the Linux kernel, the following vulnerability has been resolved:

nfc: llcp: bound the connect_sn TLV walk to the skb

Commit 27256cdb290e ("nfc: llcp: bound SNL TLV parsing to the skb and
add length checks") fixed the unbounded TLV walk in nfc_llcp_recv_snl(),
and commit d8bd2dedbde5 ("nfc: llcp: fix OOB read and u8 offset wrap in
TLV parsers") subsequently bounded nfc_llcp_parse_gb_tlv() and
nfc_llcp_parse_connection_tlv(). One sibling parser sharing the same
pattern remains unbounded: nfc_llcp_connect_sn().

nfc_llcp_connect_sn() walks a TLV list, reading a two-byte header
(type, length) followed by length bytes of value, without checking that
the two header bytes or the declared length stay within the buffer. It
returns a pointer to a service name of up to 255 bytes that may point
past the end of the skb; it is subsequently consumed by memcmp() in
nfc_llcp_sock_from_sn(). In addition tlv_array_len was computed as
"skb->len - LLCP_HEADER_SIZE" in size_t, so a CONNECT/CC frame shorter
than the LLCP header underflows to a huge length and the walk runs far
past the buffer.

nfc_llcp_connect_sn() is reachable from nfc_llcp_recv_connect() and
nfc_llcp_recv_cc(), i.e. from received CONNECT and CC PDUs. A nearby
NFC device can reach this without authentication; LLCP link activation
happens automatically after NFC-DEP, and the nfc_llcp_rx_skb()
dispatcher applies no minimum-length guard.

Walk the TLV list by pointer, bounded by skb_tail_pointer(skb), and
validate each declared length before use, matching the approach already
used for nfc_llcp_recv_snl(). Starting the walk at
&skb->data[LLCP_HEADER_SIZE] against the tail pointer also removes the
size_t underflow for short frames.

Found by 0sec automated security-research tooling (https://0sec.ai).

The Linux kernel CVE team has assigned CVE-2026-80800 to this issue.


Affected and fixed versions
===========================

	Issue introduced in 3.3 with commit d646960f7986fefb460a2b062d5ccc8ccfeacc3a and fixed in 5.10.267 with commit b2ebdfe3d5b76e91f267a61cbc3f9a0e3f77071e
	Issue introduced in 3.3 with commit d646960f7986fefb460a2b062d5ccc8ccfeacc3a and fixed in 5.15.218 with commit e18d044bab6d3d0280639098c3fe6621692cbfe2
	Issue introduced in 3.3 with commit d646960f7986fefb460a2b062d5ccc8ccfeacc3a and fixed in 6.1.185 with commit 65a0ec7783b06068dda6745dd689bf4a91ee64aa
	Issue introduced in 3.3 with commit d646960f7986fefb460a2b062d5ccc8ccfeacc3a and fixed in 6.6.154 with commit 1964addc8dd535a05d5d3b55b4d1ac19ae31aa65
	Issue introduced in 3.3 with commit d646960f7986fefb460a2b062d5ccc8ccfeacc3a and fixed in 6.12.106 with commit 389986fd79e4d43f971a03b512645a1bb63c982f
	Issue introduced in 3.3 with commit d646960f7986fefb460a2b062d5ccc8ccfeacc3a and fixed in 6.18.47 with commit e87527b506c40db9af528714b7b1240918eb80fc
	Issue introduced in 3.3 with commit d646960f7986fefb460a2b062d5ccc8ccfeacc3a and fixed in 7.1.11 with commit 22e5177ba1196a0b272a6a46c2575eb940a939c4
	Issue introduced in 3.3 with commit d646960f7986fefb460a2b062d5ccc8ccfeacc3a and fixed in 7.2.1 with commit 0cfbdb0e13ab5b0765d77f96af67eb879cbc9736
	Issue introduced in 3.3 with commit d646960f7986fefb460a2b062d5ccc8ccfeacc3a and fixed in 7.3-rc1 with commit 55c68ac93e7dacc0f5f608b9c39dd4ff48cf28e8

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2026-80800
will be updated if fixes are backported, please check that for the most
up to date information about this issue.


Affected files
==============

The file(s) affected by this issue are:
	net/nfc/llcp_core.c


Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/b2ebdfe3d5b76e91f267a61cbc3f9a0e3f77071e
	https://git.kernel.org/stable/c/e18d044bab6d3d0280639098c3fe6621692cbfe2
	https://git.kernel.org/stable/c/65a0ec7783b06068dda6745dd689bf4a91ee64aa
	https://git.kernel.org/stable/c/1964addc8dd535a05d5d3b55b4d1ac19ae31aa65
	https://git.kernel.org/stable/c/389986fd79e4d43f971a03b512645a1bb63c982f
	https://git.kernel.org/stable/c/e87527b506c40db9af528714b7b1240918eb80fc
	https://git.kernel.org/stable/c/22e5177ba1196a0b272a6a46c2575eb940a939c4
	https://git.kernel.org/stable/c/0cfbdb0e13ab5b0765d77f96af67eb879cbc9736
	https://git.kernel.org/stable/c/55c68ac93e7dacc0f5f608b9c39dd4ff48cf28e8