[PATCH] usbip: stub: keep URB array state consistent on errors

[Weiming Shi <bestswngs@gmail.com>]

stub_priv_alloc() links a zeroed stub_priv to priv_init before the URB
array is allocated.  The error handler may therefore consume the object
after stub_recv_cmd_submit() reports SDEV_EVENT_ERROR_MALLOC.

Do not publish num_urbs until the array exists.  If a later URB allocation
fails, clear the freed array pointer and count before the event handler can
walk them.  This prevents a NULL dereference on array-allocation failure
and freed-array reads that can lead to invalid URB use or a double free on
later failures.

Fixes: ea44d190764b ("usbip: Implement SG support to vhci-hcd and stub driver")
Cc: stable@vger.kernel.org # 5.4+
Reported-by: co+66c3f58096d0bde8@bugs.sh
Closes: https://lore.kernel.org/all/J3vQPnNHSkQ6YUiFvu1bk8ai3Q8aZ7a9J1Y7%40bugs.sh/
Assisted-by: Codex:gpt-5
Signed-off-by: Weiming Shi <bestswngs@gmail.com>
---
 drivers/usb/usbip/stub_rx.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/usb/usbip/stub_rx.c b/drivers/usb/usbip/stub_rx.c
index 1e9ae578810d9..33058fb05b2f4 100644
--- a/drivers/usb/usbip/stub_rx.c
+++ b/drivers/usb/usbip/stub_rx.c
@@ -534,10 +534,10 @@ static void stub_recv_cmd_submit(struct stub_device *sdev,
 	}
 
 	/* allocate urb array */
-	priv->num_urbs = num_urbs;
 	priv->urbs = kmalloc_objs(*priv->urbs, num_urbs);
 	if (!priv->urbs)
 		goto err_urbs;
+	priv->num_urbs = num_urbs;
 
 	/* setup a urb */
 	if (support_sg) {
@@ -641,6 +641,8 @@ static void stub_recv_cmd_submit(struct stub_device *sdev,
 
 err_urb:
 	kfree(priv->urbs);
+	priv->urbs = NULL;
+	priv->num_urbs = 0;
 err_urbs:
 	kfree(buffer);
 	sgl_free(sgl);
-- 
2.55.0