Re: [PATCH] staging: media: atomisp: Fix stack buffer overflow in gmin_get_var_int()

[Hans de Goede <hansg@kernel.org>]

Hi Kees,

On 29-Jul-25 2:46 AM, Kees Cook wrote:
> On Sat, Jul 26, 2025 at 02:24:51PM +0200, Hans de Goede wrote:
>> Hi Kees,
>>
>> On 24-Jul-25 10:08 AM, Kees Cook wrote:
>>> When gmin_get_config_var() calls efi.get_variable() and the EFI variable
>>> is larger than the expected buffer size, two behaviors combine to create
>>> a stack buffer overflow:
>>>
>>> 1. gmin_get_config_var() does not return the proper error code when
>>>    efi.get_variable() fails. It returns the stale 'ret' value from
>>>    earlier operations instead of indicating the EFI failure.
>>>
>>> 2. When efi.get_variable() returns EFI_BUFFER_TOO_SMALL, it updates
>>>    *out_len to the required buffer size but writes no data to the output
>>>    buffer. However, due to bug #1, gmin_get_var_int() believes the call
>>>    succeeded.
>>>
>>> The caller gmin_get_var_int() then performs:
>>> - Allocates val[CFG_VAR_NAME_MAX + 1] (65 bytes) on stack
>>> - Calls gmin_get_config_var(dev, is_gmin, var, val, &len) with len=64
>>> - If EFI variable is >64 bytes, efi.get_variable() sets len=required_size
>>> - Due to bug #1, thinks call succeeded with len=required_size
>>> - Executes val[len] = 0, writing past end of 65-byte stack buffer
>>>
>>> This creates a stack buffer overflow when EFI variables are larger than
>>> 64 bytes. Since EFI variables can be controlled by firmware or system
>>> configuration, this could potentially be exploited for code execution.
>>>
>>> Fix the bug by returning proper error codes from gmin_get_config_var()
>>> based on EFI status instead of stale 'ret' value.
>>>
>>> The gmin_get_var_int() function is called during device initialization
>>> for camera sensor configuration on Intel Bay Trail and Cherry Trail
>>> platforms using the atomisp camera stack.
>>>
>>> Reported-by: zepta <z3ptaa@gmail.com>
>>> Closes: https://lore.kernel.org/all/CAPBS6KoQyM7FMdPwOuXteXsOe44X4H3F8Fw+y_qWq6E+OdmxQA@mail.gmail.com
>>> Fixes: 38d4f74bc148 ("media: atomisp_gmin_platform: stop abusing efivar API")
>>> Signed-off-by: Kees Cook <kees@kernel.org>
>>
>> Thanks, patch looks good to me:
>>
>> Reviewed-by: Hans de Goede <hansg@kernel.org>
>>
>> I've already send an atomisp pull-request for 6.17 out
>> and this is already in media-committers/next now and
>> the media subsystem is typically not good in merging
>> fixes just before the merge window.
>>
>> Kees, the file touched here is unchanged in
>> media-committers/next vs Linus' latest master, can you
>> send this fix to Linus yourself ?
> 
> I apologize; this slipped through the cracks. Shall I take it for -rc2,
> or do you want to snag it?

I'm just back from vacation and I see you've send this
to Linus already:

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/drivers/staging/media/atomisp?id=ee4cf798202d285dcbe85e4467a094c44f5ed8e6

Which is great, thank you.

Regards,

Hans