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

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Message-ID: <CAKb7UvhTPfJhbp+h_y_C8KJa19syZX+rVN0F9S_Lkqkzc+fDoA@mail.gmail.com>
Date:	Wed, 1 Jul 2015 14:06:02 -0400
From:	Ilia Mirkin <imirkin@...m.mit.edu>
To:	Emil Velikov <emil.l.velikov@...il.com>
Cc:	Colin Ian King <colin.king@...onical.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 1:59 PM, Emil Velikov <emil.l.velikov@...il.com> wrote:
> On 1 July 2015 at 18:37, Ilia Mirkin <imirkin@...m.mit.edu> wrote:
>> 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...
> There is one:
>
> drm/nouveau/nvkm/engine/disp/nv50.c: if (nvif_unpack(args->v1, 1, 1, true))
>
> Seems like a recent addition though,  I don't recall it with back when
> was introduced.

It follows a call to nvif_unpack(0) though, which will initialize ret.
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