Re: [PATCH v2] net: core: Prevent from dereferencing null pointer when

[Myungho Jung <mhjungk@gmail.com>]

On Mon, Apr 24, 2017 at 09:44:50PM -0400, David Miller wrote:
> From: Myungho Jung <mhjungk@gmail.com>
> Date: Mon, 24 Apr 2017 18:00:52 -0700
> 
> > On Mon, Apr 24, 2017 at 12:02:35PM -0400, David Miller wrote:
> >> From: Myungho Jung <mhjungk@gmail.com>
> >> Date: Thu, 20 Apr 2017 16:59:20 -0700
> >> 
> >> > Added NULL check to make __dev_kfree_skb_irq consistent with kfree
> >> > family of functions.
> >> > 
> >> > Link: https://bugzilla.kernel.org/show_bug.cgi?id=195289
> >> > 
> >> > Signed-off-by: Myungho Jung <mhjungk@gmail.com>
> >> > ---
> >> > Changes in v2:
> >> >  - Correct category in subject
> >> 
> >> This subject line is an incomplete sentence.
> >> 
> >> This patch prevents dereferenccing a null pointer when "what"?
> > 
> > As it was reported on bugzilla, it would happen when plugging p54 usb device
> > to RPi2. But, i'm not 100% sure that this patch will resolve the issue because
> > the reporter didn't try my patch yet and I don't have the device to test.
> > 
> > And there might be some other places calling the function without checking
> > null pointer. The thing is that only the function don't check null among
> > kfree functions. So, I just hope this patch will prevent potential oops
> > issues.
> 
> It doesn't check for a NULL pointer because it is almost exclusively
> used in the interrupt paths where we know we have a non-NULL skb.

Yes, actually null is checked before calling the function in most
cases. That's why my first patch was applied not to net/core but to
p54 driver because I was worried about duplicated checking.

But, Christian suggested this patch to make it consistent with other
kfree functions and consume_skb, and Eric agreed with that.

Thanks,
Myungho