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

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Message-ID: <CACvgo52S5gxzOsckG6iretST-mMeBqKhNTREbpmqJGWD26h-Rg@mail.gmail.com>
Date:	Wed, 1 Jul 2015 18:12:48 +0100
From:	Emil Velikov <emil.l.velikov@...il.com>
To:	Ilia Mirkin <imirkin@...m.mit.edu>
Cc:	Colin 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 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?
>
I think I'm having deja-vu, but I do recall a similar mention to Ben.
Although in my defence I've assumed that nvif_unpack was a function,
as macros normally are normally all caps. Seems like the patch that
capitalises nvif_unpack never made it upstream :'-(

Cheers,
Emil
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