From 55c68ac93e7dacc0f5f608b9c39dd4ff48cf28e8 Mon Sep 17 00:00:00 2001 From: Doruk Tan Ozturk Date: Thu, 9 Jul 2026 15:12:29 +0200 Subject: [PATCH] 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). Fixes: d646960f7986 ("NFC: Initial LLCP support") Cc: stable@vger.kernel.org Assisted-by: 0sec:claude-opus-4-8 Signed-off-by: Doruk Tan Ozturk Reviewed-by: Simon Horman Link: https://patch.msgid.link/20260709131229.44477-1-doruk@0sec.ai Signed-off-by: David Heidelberg --- net/nfc/llcp_core.c | 10 ++++++---- 1 file changed, 6 insertions(+), 4 deletions(-) diff --git a/net/nfc/llcp_core.c b/net/nfc/llcp_core.c index e3b2627cb089..cac1b5487064 100644 --- a/net/nfc/llcp_core.c +++ b/net/nfc/llcp_core.c @@ -849,13 +849,16 @@ static struct nfc_llcp_sock *nfc_llcp_sock_get_sn(struct nfc_llcp_local *local, static const u8 *nfc_llcp_connect_sn(const struct sk_buff *skb, size_t *sn_len) { u8 type, length; - const u8 *tlv = &skb->data[2]; - size_t tlv_array_len = skb->len - LLCP_HEADER_SIZE, offset = 0; + const u8 *tlv = &skb->data[LLCP_HEADER_SIZE]; + const u8 *tlv_end = skb_tail_pointer(skb); - while (offset < tlv_array_len) { + while (tlv + 2 < tlv_end) { type = tlv[0]; length = tlv[1]; + if (tlv + 2 + length > tlv_end) + break; + pr_debug("type 0x%x length %d\n", type, length); if (type == LLCP_TLV_SN) { @@ -863,7 +866,6 @@ static const u8 *nfc_llcp_connect_sn(const struct sk_buff *skb, size_t *sn_len) return &tlv[2]; } - offset += length + 2; tlv += length + 2; }