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Re: [PATCH] drm: do not use device name as a format string

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On 12/06/2015 10:35 AM, Daniel Vetter wrote:
>> On 11/18/2015 06:58 PM, Nicolas Iooss wrote:
>>> drm_dev_set_unique() formats its parameter using kvasprintf() but many
>>> of its callers directly pass dev_name(dev) as printf format string,
>>> without any format parameter.  This can cause some issues when the
>>> device name contains '%' characters.
>>>
>>> To avoid any potential issue, always use "%s" when using
>>> drm_dev_set_unique() with dev_name().
> 
> Not sure this is worth it really, normally people don't place % characters
> into their device names, ever. And if they do it'll blow up. There's also
> no security issue here since userspace can't set this name.
> 
> If the maintainers of the affected drivers don't want this I won't merge
> this patch.

Actually I had the same opinion before I began to add __printf
attributes and "%s" in several places in the kernel to make
-Wformat-security useful.  This led me to discover some funny issues
like the one fixed by commit 3958b79266b1 ("configfs: fix kernel
infoleak through user-controlled format string",
https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=3958b79266b14729edd61daf9dfb84de45f4ec6d
).  The patch I sent is in fact a very small step towards making
-Wformat-security useful again to detect "real" issues.

Of course, if you do not feel it is worth it and believe that dev_name
is fully controlled by trusted sources which will never introduce any %
character, I understand your will of not merging my patch.

Regards,
Nicolas

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Re: [PATCH] drm: do not use device name as a format string Nicolas Iooss <nicolas.iooss_linux@m4x.org> - 2015-12-05 10:50 +0100
  Re: [PATCH] drm: do not use device name as a format string Daniel Vetter <daniel@ffwll.ch> - 2015-12-06 10:40 +0100
    Re: [PATCH] drm: do not use device name as a format string Nicolas Iooss <nicolas.iooss_linux@m4x.org> - 2015-12-06 11:20 +0100
      Re: [PATCH] drm: do not use device name as a format string Daniel Vetter <daniel@ffwll.ch> - 2015-12-07 08:50 +0100
        Re: [PATCH] drm: do not use device name as a format string Jani Nikula <jani.nikula@linux.intel.com> - 2015-12-07 11:00 +0100
          Re: [PATCH] drm: do not use device name as a format string Daniel Vetter <daniel@ffwll.ch> - 2015-12-07 12:50 +0100
            Re: [PATCH] drm: do not use device name as a format string Thierry Reding <thierry.reding@gmail.com> - 2015-12-07 13:40 +0100
              Re: [PATCH] drm: do not use device name as a format string Nicolas Iooss <nicolas.iooss_linux@m4x.org> - 2015-12-07 18:30 +0100

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