Re: [PATCH] usb: gadget/composite : Avoid crash with bad gadget drivers

From: Philippe De Swert
Date: Wed Aug 14 2013 - 18:40:11 EST


On 12/08/13 21:08, Felipe Balbi wrote:
On Fri, Aug 09, 2013 at 09:23:08PM +0300, Philippe De Swert wrote:
Some bad gadget drivers do not check the return status of usb_add_config.

fix the gadget driver

As stated in my comment (see below) that is indeed what should happen. But we cannot fix it in future new gadget drivers, is it thus not better
to avoid a crash? The gadget driver will not work as expected anyway when this occurs and the print will at least give an indication why.

Thus they get a not correctly initialized config and when this gadget gets
deactivated the whole kernel crashes. Since on initialization failure cdev
is set to NULL it can be used to detect this problem situation. It can be
argued that the faulty gadget driver should be fixed, but imho it is better
to avoid crashing the kernel and letting the gadget developer know he/she
is making a mistake. And have the developer of said gadget driver then fix
the problem of course.

Signed-off-by: Philippe De Swert <philippe.deswert@xxxxxxxxxxxxxxx>
drivers/usb/gadget/composite.c | 6 ++++++
1 file changed, 6 insertions(+)

diff --git a/drivers/usb/gadget/composite.c b/drivers/usb/gadget/composite.c
index 55f4df6..e019bb5 100644
--- a/drivers/usb/gadget/composite.c
+++ b/drivers/usb/gadget/composite.c
@@ -848,12 +848,18 @@ void usb_remove_config(struct usb_composite_dev *cdev,
unsigned long flags;

+ if (config->cdev == NULL) {
+ pr_warn("Calling usb_remove_config without a matching usb_add_config!\n");
+ goto end;
+ }

I would take a WARN() only, but let the crash happen and fix the gadget

Since the kernel will crash with a NULL dereference anyway is BUG_ON not a better approach then?


To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at
Please read the FAQ at