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

Overview

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).

Affected

• Linux >= d646960f7986fefb460a2b062d5ccc8ccfeacc3a < b2ebdfe3d5b76e91f267a61cbc3f9a0e3f77071e
• Linux >= d646960f7986fefb460a2b062d5ccc8ccfeacc3a < e18d044bab6d3d0280639098c3fe6621692cbfe2
• Linux >= d646960f7986fefb460a2b062d5ccc8ccfeacc3a < 65a0ec7783b06068dda6745dd689bf4a91ee64aa
• Linux >= d646960f7986fefb460a2b062d5ccc8ccfeacc3a < 1964addc8dd535a05d5d3b55b4d1ac19ae31aa65
• Linux >= d646960f7986fefb460a2b062d5ccc8ccfeacc3a < 389986fd79e4d43f971a03b512645a1bb63c982f
• Linux >= d646960f7986fefb460a2b062d5ccc8ccfeacc3a < e87527b506c40db9af528714b7b1240918eb80fc
• Linux >= d646960f7986fefb460a2b062d5ccc8ccfeacc3a < 22e5177ba1196a0b272a6a46c2575eb940a939c4
• Linux >= d646960f7986fefb460a2b062d5ccc8ccfeacc3a < 0cfbdb0e13ab5b0765d77f96af67eb879cbc9736
• Linux >= d646960f7986fefb460a2b062d5ccc8ccfeacc3a < 55c68ac93e7dacc0f5f608b9c39dd4ff48cf28e8
• Linux 3.3

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.