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

[Kees Cook]

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@xxxxxxxxx>
> > Closes: https://lore.kernel.org/all/CAPBS6KoQyM7FMdPwOuXteXsOe44X4H3F8Fw+y_qWq6E+OdmxQA@xxxxxxxxxxxxxx
> > Fixes: 38d4f74bc148 ("media: atomisp_gmin_platform: stop abusing efivar API")
> > Signed-off-by: Kees Cook <kees@xxxxxxxxxx>
> 
> Thanks, patch looks good to me:
> 
> Reviewed-by: Hans de Goede <hansg@xxxxxxxxxx>
> 
> 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?

-Kees

-- 
Kees Cook