[PATCH net-next] nfc: digital: Do not dump a NULL response in command completion

[Linmao Li]

digital_wq_cmd_complete() dumps the response data whenever cmd->resp is
not an error pointer.  However, a driver can legitimately complete a
command with no response skb at all.

digital_tg_send_psl_res() is the only caller that passes timeout=0,
meaning no response is expected once the command has been transmitted.
On that path trf7970a completes the command with

	trf->rx_skb = ERR_PTR(0);

which evaluates to NULL.  IS_ERR(NULL) is false, so the NULL response
passes the !IS_ERR() check and cmd->resp->data and cmd->resp->len are
dereferenced whenever the debug print site is enabled.  The driver
guards its own dump with "trf->rx_skb && !IS_ERR(trf->rx_skb)"; the
digital layer is missing the NULL half of that test.

Use IS_ERR_OR_NULL() so that NULL responses are skipped as well.  The
callback on that path, digital_tg_send_psl_res_complete(), never
dereferences resp and dev_kfree_skb() accepts NULL, so only the debug
dump needs fixing.

Fixes: 59ee2361c924 ("NFC Digital: Implement driver commands mechanism")
Signed-off-by: Linmao Li <lilinmao@xxxxxxxxxx>
---
A separate cleanup patch, "nfc: trf7970a: Use NULL when no response is
expected", replaces that ERR_PTR(0) with a plain NULL.  It does not
change behaviour (ERR_PTR(0) is NULL), so this fix is needed either way;
if that patch lands first, read "trf->rx_skb = NULL;" above.

Link: https://patch.msgid.link/20260706075743.564658-1-lilinmao@xxxxxxxxxx

 net/nfc/digital_core.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/nfc/digital_core.c b/net/nfc/digital_core.c
index 7cb1e6aaae90..18236221d898 100644
--- a/net/nfc/digital_core.c
+++ b/net/nfc/digital_core.c
@@ -127,7 +127,7 @@ static void digital_wq_cmd_complete(struct work_struct *work)
 
 	mutex_unlock(&ddev->cmd_lock);
 
-	if (!IS_ERR(cmd->resp))
+	if (!IS_ERR_OR_NULL(cmd->resp))
 		print_hex_dump_debug("DIGITAL RX: ", DUMP_PREFIX_NONE, 16, 1,
 				     cmd->resp->data, cmd->resp->len, false);
 
-- 
2.25.1