Subject: [PATCH net 1/2] NFC: digital: Bounds check NFC-A cascade depth in SDD response handler

From: Greg Kroah-Hartman <[email-masked]>
Date: Thu, 9 Apr 2026 17:18:14 +0200

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: "David S. Miller" <[email-masked]>
Cc: Eric Dumazet <[email-masked]>
Cc: Jakub Kicinski <[email-masked]>
Cc: Paolo Abeni <[email-masked]>
Cc: Simon Horman <[email-masked]>
Cc: Greg Kroah-Hartman <[email-masked]>
Cc: Kees Cook <[email-masked]>
Cc: Thierry Escande <[email-masked]>
Cc: Samuel Ortiz <[email-masked]>
Fixes: 2c66daecc409 ("NFC Digital: Add NFC-A technology support")
Cc: stable <[email-masked]>
Assisted-by: gregkh_clanker_t1000
Signed-off-by: Greg Kroah-Hartman <[email-masked]>
---
 net/nfc/digital_technology.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/net/nfc/digital_technology.c b/net/nfc/digital_technology.c
index 63f1b721c71d..ae63c5eb06fa 100644
--- a/net/nfc/digital_technology.c
+++ b/net/nfc/digital_technology.c
@@ -424,6 +424,12 @@ static void digital_in_recv_sdd_res(struct nfc_digital_dev *ddev, void *arg,
 		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;
-- 
2.53.0