Re: [PATCH v2] fbdev:modedb: fix a possible UAF in fb_find_mode()

[Helge Deller <deller@gmx.de>]

On 6/11/26 10:10, Geert Uytterhoeven wrote:
> Hi Tuo, Helge,
> 
> On Wed, 10 Jun 2026 at 04:50, Tuo Li <islituo@gmail.com> wrote:
>> If mode_option is NULL, it is assigned from mode_option_buf:
>>
>>    if (!mode_option) {
>>      fb_get_options(NULL, &mode_option_buf);
>>      mode_option = mode_option_buf;
>>    }
>>
>> Later, name is assigned from mode_option:
>>
>>    const char *name = mode_option;
>>
>> However, mode_option_buf is freed before name is no longer used:
>>
>>    kfree(mode_option_buf);
>>
>> while name is still accessed by:
>>
>>    if ((name_matches(db[i], name, namelen) ||
>>
>> Since name aliases mode_option_buf, this may result in a
>> use-after-free.
>>
>> Fix this by extending the lifetime of mode_option_buf until the end of the
>> function and using scope-based resource management for cleanup.
>>
>> Signed-off-by: Tuo Li <islituo@gmail.com>
>> ---
>> v2:
>> * Use scope-based resource management instead of manual kfree() calls.
>>    Thanks to Helge Deller for the helpful advice.
> 
> Thanks for your patch, which is now commit 85b6256469cebdac ("fbdev:
> modedb: fix a possible UAF in fb_find_mode()") in fbdev/for-next, and has:
> 
>      Cc: stable@vger.kernel.org # v6.5+
> 
> I believe it needs:
> Fixes: 089d924d03d5c17b ("fbdev: Read video= option with
> fb_get_option() in modedb")
> 
> and that commit entered v6.4-rc1, i.e. not v6.5?

Right, but I added the v6.5+ tag, because this patch uses the "__cleanup() based infrastructure",
which I think was introduced with v6.5.

Helge