[PATCH net] NFC: digital: bound SENSF response copy into nfc_target

[Michael Bommarito <michael.bommarito@gmail.com>]

digital_in_recv_sensf_res() copies the received SENSF response into
struct nfc_target without bounding the copy to target.sensf_res. A full
on-wire digital_sensf_res is 19 bytes long, while nfc_target stores 18
bytes, so full-length or oversized responses can overwrite adjacent
stack fields before digital_target_found() sees the target.

Reject payloads larger than struct digital_sensf_res and clamp the copy
into target.sensf_res so valid 19-byte responses keep working while the
destination buffer remains bounded.

This was confirmed by injecting an oversized SENSF_RES frame via a
patched nfcsim driver, producing a kernel panic with the overflow
pattern visible on the stack:

  Kernel panic - not syncing: Kernel mode fault at addr 0x0
  Stack:
   4141414141414141 4141414141414141 4141414141414141 ...

Found by static analysis with Coccinelle (memcpy-from-TLV pattern
derived from CVE-2019-14814).

Fixes: 8c0695e4998d ("NFC Digital: Add NFC-F technology support")
Cc: stable@vger.kernel.org
Assisted-by: Claude:claude-opus-4-6
Assisted-by: Codex:gpt-5-4
Signed-off-by: Michael Bommarito <michael.bommarito@gmail.com>
---
 net/nfc/digital_technology.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/net/nfc/digital_technology.c b/net/nfc/digital_technology.c
index 63f1b721c71d..5ef49f813f70 100644
--- a/net/nfc/digital_technology.c
+++ b/net/nfc/digital_technology.c
@@ -768,12 +768,18 @@ static void digital_in_recv_sensf_res(struct nfc_digital_dev *ddev, void *arg,
 
 	skb_pull(resp, 1);
 
+	if (resp->len > sizeof(struct digital_sensf_res)) {
+		rc = -EIO;
+		goto exit;
+	}
+
 	memset(&target, 0, sizeof(struct nfc_target));
 
 	sensf_res = (struct digital_sensf_res *)resp->data;
 
-	memcpy(target.sensf_res, sensf_res, resp->len);
-	target.sensf_res_len = resp->len;
+	target.sensf_res_len = min_t(unsigned int, resp->len,
+				     sizeof(target.sensf_res));
+	memcpy(target.sensf_res, sensf_res, target.sensf_res_len);
 
 	memcpy(target.nfcid2, sensf_res->nfcid2, NFC_NFCID2_MAXSIZE);
 	target.nfcid2_len = NFC_NFCID2_MAXSIZE;
-- 
2.53.0