[PATCH] usb: gadget: u_ether: Fix NULL pointer deref in eth_get_drvinfo

[Kuen-Han Tsai <khtsai@google.com>]

Commit ec35c1969650 ("usb: gadget: f_ncm: Fix net_device lifecycle with
device_move") reparents the gadget device to /sys/devices/virtual during
unbind, clearing the gadget pointer. If the userspace tool queries on
the surviving interface during this detached window, this leads to a
NULL pointer dereference.

Unable to handle kernel NULL pointer dereference
Call trace:
 eth_get_drvinfo+0x50/0x90
 ethtool_get_drvinfo+0x5c/0x1f0
 __dev_ethtool+0xaec/0x1fe0
 dev_ethtool+0x134/0x2e0
 dev_ioctl+0x338/0x560

Add a NULL check for dev->gadget in eth_get_drvinfo(). When detached,
skip copying the fw_version and bus_info strings, which is natively
handled by ethtool_get_drvinfo for empty strings.

Suggested-by: Val Packett <val@packett.cool>
Reported-by: Val Packett <val@packett.cool>
Closes: https://lore.kernel.org/linux-usb/10890524-cf83-4a71-b879-93e2b2cc1fcc@packett.cool/
Fixes: ec35c1969650 ("usb: gadget: f_ncm: Fix net_device lifecycle with device_move")
Cc: stable@vger.kernel.org
Signed-off-by: Kuen-Han Tsai <khtsai@google.com>
---
 drivers/usb/gadget/function/u_ether.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/usb/gadget/function/u_ether.c b/drivers/usb/gadget/function/u_ether.c
index 1a9e7c495e2e..a653fae9c0cb 100644
--- a/drivers/usb/gadget/function/u_ether.c
+++ b/drivers/usb/gadget/function/u_ether.c
@@ -113,8 +113,10 @@ static void eth_get_drvinfo(struct net_device *net, struct ethtool_drvinfo *p)
 
 	strscpy(p->driver, "g_ether", sizeof(p->driver));
 	strscpy(p->version, UETH__VERSION, sizeof(p->version));
-	strscpy(p->fw_version, dev->gadget->name, sizeof(p->fw_version));
-	strscpy(p->bus_info, dev_name(&dev->gadget->dev), sizeof(p->bus_info));
+	if (dev->gadget) {
+		strscpy(p->fw_version, dev->gadget->name, sizeof(p->fw_version));
+		strscpy(p->bus_info, dev_name(&dev->gadget->dev), sizeof(p->bus_info));
+	}
 }
 
 /* REVISIT can also support:

---
base-commit: d0d9b1f4f5391e6a00cee81d73ed2e8f98446d5f
change-id: 20260316-eth-null-deref-0304bb048267

Best regards,
-- 
Kuen-Han Tsai <khtsai@google.com>