Re: [PATCH v2 1/7] malloc: Add check for top size corruption.

[Florian Weimer <fweimer at redhat dot com>]

On 11/07/2017 04:27 PM, Istvan Kurucsai wrote:
> Ensure that the size of top is below av->system_mem.
>
>      * malloc/malloc.c (_int_malloc): Check top size.
> ---
>   malloc/malloc.c | 4 ++++
>   1 file changed, 4 insertions(+)
>
> diff --git a/malloc/malloc.c b/malloc/malloc.c
> index f94d51c..4a30c42 100644
> --- a/malloc/malloc.c
> +++ b/malloc/malloc.c
> @@ -4078,6 +4078,10 @@ _int_malloc (mstate av, size_t bytes)
>   
>         if ((unsigned long) (size) >= (unsigned long) (nb + MINSIZE))
>           {
> +          if (__glibc_unlikely ((unsigned long) (size) >
> +                                (unsigned long) (av->system_mem)))
> +            malloc_printerr("malloc(): corrupted top chunk");
> +

Andreas already pointed out style issues.

I'm somewhat surprised that we have accurate accounting in av->system_mem.

Furthermore, for non-main arenas, I think the check should be against 
the size of a single heap, or maybe the minimum of av->system_mem and 
that size.

Thanks,
Florian