5.10-stable review patch. If anyone has any objections, please let me know. ------------------ From: Doruk Tan Ozturk [ Upstream commit f4c7f37f0ab990952539dc68d931d65c3657600a ] nfc_llcp_recv_snl() walked the SNL TLV list using a u16 offset/length pair derived from skb->len, without bounding reads to the actual skb data. Three problems followed: - For a short frame (skb->len < LLCP_HEADER_SIZE), tlv_len underflowed. - The per-TLV header (type, length) was read without checking that two bytes remained. - A declared TLV length could run past the end of the buffer, and an SDREQ with length == 0 made "service_name_len = length - 1" underflow (size_t), driving an out-of-bounds read in the following strncmp() / nfc_llcp_sock_from_sn(). The SDRES case likewise read tlv[2]/tlv[3] without a length check. A nearby NFC device can reach this without authentication; LLCP link activation happens automatically after NFC-DEP. Walk the TLV list by pointer, bounded by skb_tail_pointer() over the linear skb data, and validate each TLV declared length before use. Add explicit length checks for SDREQ (>= 1) and SDRES (exactly 2). Found by 0sec automated security-research tooling (https://0sec.ai). Fixes: 19cfe5843e86 ("NFC: Initial SNL support") Signed-off-by: Doruk Tan Ozturk Reviewed-by: Simon Horman Link: https://patch.msgid.link/20260609202543.42282-1-doruk@0sec.ai Signed-off-by: David Heidelberg Signed-off-by: Sasha Levin --- net/nfc/llcp_core.c | 29 +++++++++++++++++++++-------- 1 file changed, 21 insertions(+), 8 deletions(-) diff --git a/net/nfc/llcp_core.c b/net/nfc/llcp_core.c index c5971ccd33ea9..a0b4559d8edc7 100644 --- a/net/nfc/llcp_core.c +++ b/net/nfc/llcp_core.c @@ -1295,10 +1295,9 @@ static void nfc_llcp_recv_snl(struct nfc_llcp_local *local, { struct nfc_llcp_sock *llcp_sock; u8 dsap, ssap, type, length, tid, sap; - const u8 *tlv; - u16 tlv_len, offset; + const u8 *tlv, *tlv_end; const char *service_name; - size_t service_name_len; + int service_name_len; struct nfc_llcp_sdp_tlv *sdp; HLIST_HEAD(llc_sdres_list); size_t sdres_tlvs_len; @@ -1314,22 +1313,34 @@ static void nfc_llcp_recv_snl(struct nfc_llcp_local *local, return; } + /* + * Walk the SNL TLV list in the linear part of the skb only, + * bounded by skb_tail_pointer(). Each TLV needs a two-byte + * header (type, length) and its declared length must fit before + * the end; this also keeps the walk safe for very short frames. + */ tlv = &skb->data[LLCP_HEADER_SIZE]; - tlv_len = skb->len - LLCP_HEADER_SIZE; - offset = 0; + tlv_end = skb_tail_pointer(skb); sdres_tlvs_len = 0; - while (offset < tlv_len) { + while (tlv + 2 < tlv_end) { type = tlv[0]; length = tlv[1]; + if (tlv + 2 + length > tlv_end) + break; + switch (type) { case LLCP_TLV_SDREQ: + if (length < 1) + break; + tid = tlv[2]; service_name = (char *) &tlv[3]; service_name_len = length - 1; - pr_debug("Looking for %.16s\n", service_name); + pr_debug("Looking for %.*s\n", service_name_len, + service_name); if (service_name_len == strlen("urn:nfc:sn:sdp") && !strncmp(service_name, "urn:nfc:sn:sdp", @@ -1389,6 +1400,9 @@ static void nfc_llcp_recv_snl(struct nfc_llcp_local *local, break; case LLCP_TLV_SDRES: + if (length != 2) + break; + mutex_lock(&local->sdreq_lock); pr_debug("LLCP_TLV_SDRES: searching tid %d\n", tlv[2]); @@ -1417,7 +1431,6 @@ static void nfc_llcp_recv_snl(struct nfc_llcp_local *local, break; } - offset += length + 2; tlv += length + 2; } -- 2.53.0