[PATCH net] nfc: llcp: validate TLV length before parsing to fix OOB read

[Weiming Shi <bestswngs@gmail.com>]

nfc_llcp_parse_gb_tlv() and nfc_llcp_parse_connection_tlv() iterate over
a TLV array supplied by the remote peer. Each iteration reads the type
and length from tlv[0]/tlv[1] and then advances by length + 2, but the
loop only tests offset < tlv_array_len and never checks that the 2-byte
header fits in the remaining space. A truncated trailing entry is enough
to read past the buffer on the tlv[1] access.

The length byte then makes it worse. offset is a u8, so length + 2 wraps
at 256: length == 0xff advances by 0x101 and leaves offset unchanged, so
the loop stays live while tlv keeps moving forward. The parse walks well
past the buffer, and the next iteration's tlv[0]/tlv[1] read lands out of
bounds rather than the walk stopping one entry over.

nfc_llcp_parse_gb_tlv() runs on the general bytes of an activated
NFC-DEP link. An RF_INTF_ACTIVATED_NTF in listen mode reaches it via
nci_ntf_packet() -> nfc_tm_activated() -> nfc_llcp_set_remote_gb(), which
copies the peer's general bytes into the 48-byte remote_gb[] field of the
heap-allocated struct nfc_llcp_local; the wrapped walk runs off the end
of that allocation. nfc_llcp_parse_connection_tlv() is reached the same
way from CONNECT/CC PDUs, over tlv data taken from the received skb.

Bound each iteration to tlv_array_len before touching the header, and
widen offset to u16 so the advance can no longer wrap. Well-formed TLVs
are parsed as before; a malformed trailing entry ends the loop.

 BUG: KASAN: slab-out-of-bounds in nfc_llcp_parse_gb_tlv (net/nfc/llcp_commands.c:204)
 Read of size 1 by task kworker/u8:3
  nfc_llcp_parse_gb_tlv (net/nfc/llcp_commands.c:204)
  nfc_llcp_set_remote_gb (net/nfc/llcp_core.c:681)
  nfc_tm_activated (net/nfc/core.c:643 net/nfc/core.c:677)
  nci_ntf_packet (net/nfc/nci/ntf.c:883 net/nfc/nci/ntf.c:1015)
  nci_rx_work (net/nfc/nci/core.c:1564)

Fixes: d646960f7986 ("NFC: Initial LLCP support")
Reported-by: Xiang Mei <xmei5@asu.edu>
Assisted-by: Claude:claude-opus-4-8
Signed-off-by: Weiming Shi <bestswngs@gmail.com>
---
 net/nfc/llcp_commands.c | 16 ++++++++++++----
 1 file changed, 12 insertions(+), 4 deletions(-)

diff --git a/net/nfc/llcp_commands.c b/net/nfc/llcp_commands.c
index 291f26facbf3..3f0f8eef9890 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;
+	u8 type, length;
+	u16 offset = 0;
 
 	pr_debug("TLV array length %d\n", tlv_array_len);
 
 	if (local == NULL)
 		return -ENODEV;
 
-	while (offset < tlv_array_len) {
+	while (offset + 2 <= tlv_array_len) {
 		type = tlv[0];
 		length = tlv[1];
 
+		if (offset + 2 + length > tlv_array_len)
+			break;
+
 		pr_debug("type 0x%x length %d\n", type, length);
 
 		switch (type) {
@@ -243,17 +247,21 @@ 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;
+	u8 type, length;
+	u16 offset = 0;
 
 	pr_debug("TLV array length %d\n", tlv_array_len);
 
 	if (sock == NULL)
 		return -ENOTCONN;
 
-	while (offset < tlv_array_len) {
+	while (offset + 2 <= tlv_array_len) {
 		type = tlv[0];
 		length = tlv[1];
 
+		if (offset + 2 + length > tlv_array_len)
+			break;
+
 		pr_debug("type 0x%x length %d\n", type, length);
 
 		switch (type) {
-- 
2.43.0