Re: kernel oops

From: Vegard Nossum
Date: Wed Jul 23 2008 - 11:12:03 EST


On Wed, Jul 23, 2008 at 2:52 PM, Andrei Popa <andrei.popa@xxxxxxxx> wrote:
> Hello,
> I installed gnokii-0.6.22-r2 and gave the command "gnokii --identify"
> and the kernel oopsed:
> BUG: unable to handle kernel NULL pointer dereference at 00000458
> IP: [<c0444b52>] mutex_unlock+0x0/0xb
> *pde = 00000000
> Oops: 0002 [#1] PREEMPT SMP
> Pid: 19043, comm: gnokii Not tainted (2.6.26-ineo7 #2)
> EIP: 0060:[<c0444b52>] EFLAGS: 00010246 CPU: 0
> EIP is at mutex_unlock+0x0/0xb
> [<c03830ae>] acm_tty_open+0x4c/0x214

This shouldn't be too hard; the code is trying to unlock the mutex
&acm->mutex even when "acm" is NULL. It seems that the label "err_out"
is otherwise unused, so it makes sense to move this one step further
down, so that it doesn't try to unlock the non-existant mutex.

If the problem is reproducible, you could try the patch below!


PS: I actually think the code has some other problems too. Shouldn't
&acm->mutex be locked before we even inspect acm->dev?

Reported-by: Andrei Popa <andrei.popa@xxxxxxxx>
Signed-off-by: Vegard Nossum <vegard.nossum@xxxxxxxxx>

diff --git a/drivers/usb/class/cdc-acm.c b/drivers/usb/class/cdc-acm.c
index 63c3404..74d03a7 100644
--- a/drivers/usb/class/cdc-acm.c
+++ b/drivers/usb/class/cdc-acm.c
@@ -525,8 +525,8 @@ static int acm_tty_open(struct tty_struct *tty, struct file *filp)

return rv;

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