[PATCH] gpib: agilent_82357a: don't check a NULL serial string

[Joe Simmons-Talbott <joest@redhat.com>]

The agilent_82357a driver uses the USB device serial string for device
matching but does not verify that the string exists before passing it
to strcmp().

Verify that the device has a serial number before accessing it to avoid
triggering a NULL-pointer dereference with devices that don't provide
a serial number (iSerialNumber = 0).

Similar to commit aa79f996eb41 ("i2c: cp2615: fix serial string
NULL-deref at probe").

Found by Claude:sonnet-4.5

Signed-off-by: Joe Simmons-Talbott <joest@redhat.com>
---
 drivers/gpib/agilent_82357a/agilent_82357a.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/gpib/agilent_82357a/agilent_82357a.c b/drivers/gpib/agilent_82357a/agilent_82357a.c
index e1349afbf933..da046ea40f11 100644
--- a/drivers/gpib/agilent_82357a/agilent_82357a.c
+++ b/drivers/gpib/agilent_82357a/agilent_82357a.c
@@ -1298,7 +1298,7 @@ static inline int agilent_82357a_device_match(struct usb_interface *interface,
 	if (gpib_match_device_path(&interface->dev, config->device_path) == 0)
 		return 0;
 	if (config->serial_number &&
-	    strcmp(usbdev->serial, config->serial_number) != 0)
+	    (!usbdev->serial || strcmp(usbdev->serial, config->serial_number) != 0))
 		return 0;
 
 	return 1;
-- 
2.53.0