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Sun, 05 Jul 2026 04:56:09 -0700 (PDT) Received: from PeakBook-Mini.tail8e484.ts.net ([178.197.219.178]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-493c636ec8asm238396105e9.1.2026.07.05.04.56.08 (version=TLS1_3 cipher=TLS_CHACHA20_POLY1305_SHA256 bits=256/256); Sun, 05 Jul 2026 04:56:09 -0700 (PDT) From: Doruk Tan Ozturk To: David Heidelberg , oe-linux-nfc@lists.linux.dev Cc: Simon Horman , David Laight , netdev@vger.kernel.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org, Doruk Tan Ozturk Subject: [PATCH net] nfc: llcp: bound the remaining LLCP TLV parsers to their buffers Date: Sun, 5 Jul 2026 13:56:07 +0200 Message-ID: <20260705115607.60844-1-doruk@0sec.ai> X-Mailer: git-send-email 2.53.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 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(), but three sibling parsers that share the exact same pattern were left unbounded: - nfc_llcp_parse_gb_tlv() - nfc_llcp_parse_connection_tlv() - nfc_llcp_connect_sn() Each 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. nfc_llcp_connect_sn() then 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(). nfc_llcp_parse_connection_tlv() is worse: it tracks the walk offset in a u8, so a single crafted TLV with length == 254 advances the offset by 256, which wraps to 0. The loop condition "offset < tlv_array_len" then never makes progress while the tlv pointer keeps marching forward, producing an infinite loop with a runaway out-of-bounds read and a guaranteed oops even without KASAN. nfc_llcp_parse_connection_tlv() and nfc_llcp_connect_sn() are 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 each TLV list by pointer, bounded by the end of the buffer (skb_tail_pointer() for connect_sn, tlv_array + tlv_array_len for the gb and connection parsers), and validate each declared length before use, matching the approach already used for nfc_llcp_recv_snl(). Dropping the u8 offset also removes the wrap, and for very short connect frames this avoids the size_t underflow of "skb->len - LLCP_HEADER_SIZE". 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 --- net/nfc/llcp_commands.c | 18 ++++++++++++------ net/nfc/llcp_core.c | 10 ++++++---- 2 files changed, 18 insertions(+), 10 deletions(-) diff --git a/net/nfc/llcp_commands.c b/net/nfc/llcp_commands.c index 291f26facbf3..1a0a2f4aca70 100644 --- a/net/nfc/llcp_commands.c +++ b/net/nfc/llcp_commands.c @@ -193,17 +193,21 @@ int nfc_llcp_parse_gb_tlv(struct nfc_llcp_local *local, const u8 *tlv_array, u16 tlv_array_len) { const u8 *tlv = tlv_array; - u8 type, length, offset = 0; + const u8 *tlv_end = tlv_array + tlv_array_len; + u8 type, length; pr_debug("TLV array length %d\n", tlv_array_len); if (local == NULL) return -ENODEV; - 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); switch (type) { @@ -227,7 +231,6 @@ int nfc_llcp_parse_gb_tlv(struct nfc_llcp_local *local, break; } - offset += length + 2; tlv += length + 2; } @@ -243,17 +246,21 @@ int nfc_llcp_parse_connection_tlv(struct nfc_llcp_sock *sock, const u8 *tlv_array, u16 tlv_array_len) { const u8 *tlv = tlv_array; - u8 type, length, offset = 0; + const u8 *tlv_end = tlv_array + tlv_array_len; + u8 type, length; pr_debug("TLV array length %d\n", tlv_array_len); if (sock == NULL) return -ENOTCONN; - 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); switch (type) { @@ -270,7 +277,6 @@ int nfc_llcp_parse_connection_tlv(struct nfc_llcp_sock *sock, break; } - offset += length + 2; tlv += length + 2; } diff --git a/net/nfc/llcp_core.c b/net/nfc/llcp_core.c index aed5fe1afef0..0de20279e046 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; } -- 2.43.0