[PATCH v6] nfc: hci: fix out-of-bounds read in HCP header parsing

[Ashutosh Desai <ashutoshdesai993@gmail.com>]

Both nfc_hci_recv_from_llc() and nci_hci_data_received_cb() read
packet->header from skb->data at function entry without first checking
that the buffer holds at least one byte. A malicious NFC peer can send
a 0-byte HCP frame that passes through the SHDLC layer and reaches
these functions, causing an out-of-bounds heap read of packet->header.
The same 0-byte frame, if queued as a non-final fragment, also causes
the reassembly loop to underflow msg_len to UINT_MAX, triggering
skb_over_panic() when the reassembled skb is written.

Fix this by adding a pskb_may_pull() check at the entry of each
function before packet->header is first accessed. The existing
pskb_may_pull() checks before the reassembled hcp_skb is cast to
struct hcp_packet remain in place to guard the 2-byte HCP message
header.

Fixes: 8b8d2e08bf0d ("NFC: HCI support")
Fixes: 11f54f228643 ("NFC: nci: Add HCI over NCI protocol support")
Cc: stable@vger.kernel.org
Reviewed-by: Simon Horman <horms@kernel.org>
Signed-off-by: Ashutosh Desai <ashutoshdesai993@gmail.com>
---
Changes in v6:
- Add pskb_may_pull(skb, 1) at function entry in both functions before
  packet->header is first accessed, to fix OOB read on 0-byte frames
  and prevent integer underflow in the fragment reassembly path
  (Paolo Abeni)

V5 -> V6: add entry-point length checks per Paolo Abeni's review
V4 -> V5: fix whitespace damage
V3 -> V4: add Fixes tags
V2 -> V3: drop redundant checks from nfc_hci_msg_rx_work/nci_hci_msg_rx_work;
          remove incorrect Suggested-by tag
V1 -> V2: use pskb_may_pull() instead of skb->len check

v5: https://lore.kernel.org/netdev/20260416051522.4154698-1-ashutoshdesai993@gmail.com/
v4: https://lore.kernel.org/netdev/177614425081.3600288.2536320552978506086@gmail.com/
v3: https://lore.kernel.org/netdev/20260413024329.3293075-1-ashutoshdesai993@gmail.com/
v2: https://lore.kernel.org/netdev/20260409150825.2217133-1-ashutoshdesai993@gmail.com/
v1: https://lore.kernel.org/netdev/20260408223113.2009304-1-ashutoshdesai993@gmail.com/

 net/nfc/hci/core.c | 10 ++++++++++
 net/nfc/nci/hci.c  | 10 ++++++++++
 2 files changed, 20 insertions(+)

diff --git a/net/nfc/hci/core.c b/net/nfc/hci/core.c
index 0d33c81a15fe..ba6f0310ffd7 100644
--- a/net/nfc/hci/core.c
+++ b/net/nfc/hci/core.c
@@ -861,6 +861,11 @@ static void nfc_hci_recv_from_llc(struct nfc_hci_dev *hdev, struct sk_buff *skb)
 	struct sk_buff *frag_skb;
 	int msg_len;
 
+	if (!pskb_may_pull(skb, NFC_HCI_HCP_PACKET_HEADER_LEN)) {
+		kfree_skb(skb);
+		return;
+	}
+
 	packet = (struct hcp_packet *)skb->data;
 	if ((packet->header & ~NFC_HCI_FRAGMENT) == 0) {
 		skb_queue_tail(&hdev->rx_hcp_frags, skb);
@@ -904,6 +909,11 @@ static void nfc_hci_recv_from_llc(struct nfc_hci_dev *hdev, struct sk_buff *skb)
 	 * unblock waiting cmd context. Otherwise, enqueue to dispatch
 	 * in separate context where handler can also execute command.
 	 */
+	if (!pskb_may_pull(hcp_skb, NFC_HCI_HCP_HEADER_LEN)) {
+		kfree_skb(hcp_skb);
+		return;
+	}
+
 	packet = (struct hcp_packet *)hcp_skb->data;
 	type = HCP_MSG_GET_TYPE(packet->message.header);
 	if (type == NFC_HCI_HCP_RESPONSE) {
diff --git a/net/nfc/nci/hci.c b/net/nfc/nci/hci.c
index 40ae8e5a7ec7..c03e8a0bd3bd 100644
--- a/net/nfc/nci/hci.c
+++ b/net/nfc/nci/hci.c
@@ -439,6 +439,11 @@ void nci_hci_data_received_cb(void *context,
 		return;
 	}
 
+	if (!pskb_may_pull(skb, NCI_HCI_HCP_PACKET_HEADER_LEN)) {
+		kfree_skb(skb);
+		return;
+	}
+
 	packet = (struct nci_hcp_packet *)skb->data;
 	if ((packet->header & ~NCI_HCI_FRAGMENT) == 0) {
 		skb_queue_tail(&ndev->hci_dev->rx_hcp_frags, skb);
@@ -482,6 +487,11 @@ void nci_hci_data_received_cb(void *context,
 	 * unblock waiting cmd context. Otherwise, enqueue to dispatch
 	 * in separate context where handler can also execute command.
 	 */
+	if (!pskb_may_pull(hcp_skb, NCI_HCI_HCP_HEADER_LEN)) {
+		kfree_skb(hcp_skb);
+		return;
+	}
+
 	packet = (struct nci_hcp_packet *)hcp_skb->data;
 	type = NCI_HCP_MSG_GET_TYPE(packet->message.header);
 	if (type == NCI_HCI_HCP_RESPONSE) {
-- 
2.34.1