linux-kernel - Re: [PATCH] drm/nouveau: usif_ioctl: ensure returns are initialized

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Date:	Wed, 1 Jul 2015 13:37:15 -0400
From:	Ilia Mirkin <imirkin@...m.mit.edu>
To:	Colin Ian King <colin.king@...onical.com>
Cc:	Emil Velikov <emil.l.velikov@...il.com>,
	Ben Skeggs <bskeggs@...hat.com>,
	"dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] drm/nouveau: usif_ioctl: ensure returns are initialized

On Wed, Jul 1, 2015 at 1:18 PM, Colin Ian King <colin.king@...onical.com> wrote:
> On 01/07/15 18:12, Emil Velikov wrote:
>> On 1 July 2015 at 17:56, Ilia Mirkin <imirkin@...m.mit.edu> wrote:
>>> On Wed, Jul 1, 2015 at 12:51 PM, Colin King <colin.king@...onical.com> wrote:
>>>> From: Colin Ian King <colin.king@...onical.com>
>>>>
>>>> Various usif_ioctl helper functions do not initialize the
>>>> return variable ret and some of the error handling return
>>>> paths just return garbage values that were on the stack (or
>>>> in a register).  I believe that in all the cases, the
>>>> initial ret variable should be set to -EINVAL and subsequent
>>>> paths through these helper functions set it appropriately
>>>> otherwise.
>>>>
>>>> Found via static analysis using cppcheck:
>>>>
>>>> [drivers/gpu/drm/nouveau/nouveau_usif.c:138]:
>>>>     (error) Uninitialized variable: ret
>>>
>>> It sure would seem that way, wouldn't it?
>>>
>>> #define nvif_unpack(d,vl,vh,m) ({                                              \
>>>         if ((vl) == 0 || ret == -ENOSYS) {                                     \
>>>                 int _size = sizeof(d);                                         \
>>>                 if (_size <= size && (d).version >= (vl) &&                    \
>>>                                      (d).version <= (vh)) {                    \
>>>                         data = (u8 *)data + _size;                             \
>>>                         size = size - _size;                                   \
>>>                         ret = ((m) || !size) ? 0 : -E2BIG;                     \
>>>                 } else {                                                       \
>>>                         ret = -ENOSYS;                                         \
>>>                 }                                                              \
>>>         }                                                                      \
>>>         (ret == 0);                                                            \
>>> })
>>>
>>> So actually it does get initialized, and I guess cppcheck doesn't know
>>> about macros?
>
> Hrm, what about the case when ((vl) == 0 || ret == -ENOSYS) is false,
> where is ret being set in that case?

Is that actually the case for any of the callsites? gcc would complain
about that...
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