[PATCH 6.6 074/166] NFC: digital: Bounds check NFC-A cascade depth in SDD response handler

Greg Kroah-Hartman
2026-04-24T13:36:40Z

From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

commit 46ce8be2ced389bccd84bcc04a12cf2f4d0c22d1 upstream.

The NFC-A anti-collision cascade in digital_in_recv_sdd_res() appends 3
or 4 bytes to target->nfcid1 on each round, but the number of cascade
rounds is controlled entirely by the peer device. The peer sets the
cascade tag in the SDD_RES (deciding 3 vs 4 bytes) and the
cascade-incomplete bit in the SEL_RES (deciding whether another round
follows).

ISO 14443-3 limits NFC-A to three cascade levels and target->nfcid1 is
sized accordingly (NFC_NFCID1_MAXSIZE = 10), but nothing in the driver
actually enforces this. This means a malicious peer can keep the
cascade running, writing past the heap-allocated nfc_target with each
round.

Fix this by rejecting the response when the accumulated UID would exceed
the buffer.

Commit e329e71013c9 ("NFC: nci: Bounds check struct nfc_target arrays")
fixed similar missing checks against the same field on the NCI path.

Cc: Simon Horman <horms@kernel.org>
Cc: Kees Cook <kees@kernel.org>
Cc: Thierry Escande <thierry.escande@linux.intel.com>
Cc: Samuel Ortiz <sameo@linux.intel.com>
Fixes: 2c66daecc409 ("NFC Digital: Add NFC-A technology support")
Cc: stable <stable@kernel.org>
Assisted-by: gregkh_clanker_t1000
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Link: https://patch.msgid.link/2026040913-figure-seducing-bd3f@gregkh
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
net/nfc/digital_technology.c | 6 ++++++
1 file changed, 6 insertions(+)

--- a/net/nfc/digital_technology.c
+++ b/net/nfc/digital_technology.c
@@ -424,6 +424,12 @@ static void digital_in_recv_sdd_res(stru
size = 4;
}

+ if (target->nfcid1_len + size > NFC_NFCID1_MAXSIZE) {
+ PROTOCOL_ERR("4.7.2.1");
+ rc = -EPROTO;
+ goto exit;
+ }
+
memcpy(target->nfcid1 + target->nfcid1_len, sdd_res->nfcid1 + offset,
size);
target->nfcid1_len += size;