Re: [PATCH i-g-t] lib/igt_hook: Fix realloc size to avoid memory overwriting

[Gustavo Sousa <gustavo.sousa@intel.com>]

Zbigniew Kempczyński <zbigniew.kempczynski@intel.com> writes:

> On Mon, Jun 29, 2026 at 09:17:53AM -0300, Gustavo Sousa wrote:
>> Zbigniew Kempczyński <zbigniew.kempczynski@intel.com> writes:
>> 
>> > Doubling test name size might be not enough for realloc if target name
>> > length is larger than test/subtest name size.
>> >
>> > Signed-off-by: Zbigniew Kempczyński <zbigniew.kempczynski@intel.com>
>> > Cc: Gustavo Sousa <gustavo.sousa@intel.com>
>> > Cc: Ryszard Knop <ryszard.knop@intel.com>
>> > ---
>> >  lib/igt_hook.c | 2 +-
>> >  1 file changed, 1 insertion(+), 1 deletion(-)
>> >
>> > diff --git a/lib/igt_hook.c b/lib/igt_hook.c
>> > index b8f25b6c7a..a44b852da1 100644
>> > --- a/lib/igt_hook.c
>> > +++ b/lib/igt_hook.c
>> > @@ -300,7 +300,7 @@ static void igt_hook_update_test_name_pre_call(struct igt_hook *igt_hook, struct
>> >  	if (len + 1 > *size_ptr) {
>> >  		size_t fullname_size;
>> >  
>> > -		*size_ptr *= 2;
>> > +		*size_ptr += len + 1;
>> 
>> Oops. My bad. Thanks for finding this!
>> 
>> Do we need to use "+=" instead of "=" above, though?
>> 
>> Also, perhaps we could use roundup_power_of_two(len + 1) to reduce the
>> number of follow-up reallocs?
>
> Sorry, I haven't explained why I used "+=" instead of "=". That was
> first what comes to my mind to fix the issue and try to decrease number
> of reallocs more than with simple '='. For smaller sizes I'm not sure if
> size of power of two is better than any other value. Glibc adds some
> overhead to malloc so I think any strategy we pick which increases
> buffer underneath is acceptable to me.

I just though "+=" adding exactly the size needed as an "extra" looked
odd and didn't initially get that this indeed had the objective of
avoiding extra reallocs in the future. I wonder if future readers of the
code will get the same perception or if that's just me.

--
Gustavo Sousa

>
> --
> Zbigniew
>
>
>> 
>> --
>> Gustavo Sousa
>> 
>> >  		*name_ptr = realloc(*name_ptr, *size_ptr);
>> >  
>> >  		fullname_size = igt_hook_calc_test_fullname_size(igt_hook);
>> > -- 
>> > 2.54.0