[PATCH] drivers/net/wan/hdlc_ppp: fix potential null pointer in ppp_cp_event logging

[Kriish Sharma]

Fixes warnings observed during compilation with -Wformat-overflow:

drivers/net/wan/hdlc_ppp.c: In function ‘ppp_cp_event’:
drivers/net/wan/hdlc_ppp.c:353:17: warning: ‘%s’ directive argument is null [-Wformat-overflow=]
  353 |                 netdev_info(dev, "%s down\n", proto_name(pid));
      |                 ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
drivers/net/wan/hdlc_ppp.c:342:17: warning: ‘%s’ directive argument is null [-Wformat-overflow=]
  342 |                 netdev_info(dev, "%s up\n", proto_name(pid));
      |                 ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Introduce local variable `pname` and fallback to "unknown" if proto_name(pid)
returns NULL.

Fixes: 262858079afd ("Add linux-next specific files for 20250926")
Signed-off-by: Kriish Sharma <kriish.sharma2006@xxxxxxxxx>
---
 drivers/net/wan/hdlc_ppp.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/drivers/net/wan/hdlc_ppp.c b/drivers/net/wan/hdlc_ppp.c
index 7496a2e9a282..f3b3fa8d46fd 100644
--- a/drivers/net/wan/hdlc_ppp.c
+++ b/drivers/net/wan/hdlc_ppp.c
@@ -339,7 +339,9 @@ static void ppp_cp_event(struct net_device *dev, u16 pid, u16 event, u8 code,
 		ppp_tx_cp(dev, pid, CP_CODE_REJ, ++ppp->seq, len, data);
 
 	if (old_state != OPENED && proto->state == OPENED) {
-		netdev_info(dev, "%s up\n", proto_name(pid));
+		const char *pname = proto_name(pid);
+
+		netdev_info(dev, "%s up\n", pname ? pname : "unknown");
 		if (pid == PID_LCP) {
 			netif_dormant_off(dev);
 			ppp_cp_event(dev, PID_IPCP, START, 0, 0, 0, NULL);
@@ -350,7 +352,9 @@ static void ppp_cp_event(struct net_device *dev, u16 pid, u16 event, u8 code,
 		}
 	}
 	if (old_state == OPENED && proto->state != OPENED) {
-		netdev_info(dev, "%s down\n", proto_name(pid));
+		const char *pname = proto_name(pid);
+
+		netdev_info(dev, "%s down\n", pname ? pname : "unknown");
 		if (pid == PID_LCP) {
 			netif_dormant_on(dev);
 			ppp_cp_event(dev, PID_IPCP, STOP, 0, 0, 0, NULL);
-- 
2.34.1