Re: [PATCH] nano-mallocr: Prevent NULL pointer de-reference in free_list

[Henrik Nilsson <henrik.nilsson@bytequest.se>]

On Fri, Feb 17, 2023 at 06:56:49AM +0100, Henrik Nilsson wrote:
> The existing code checked if there was a chunk in free_list and
> that the tail was not the next chunk.
> 
> The check if there is a chunk is not needed since it's already
> known but the case of a single chunk in free_list needs to be
> handled differently.
> ---
>  newlib/libc/stdlib/nano-mallocr.c | 19 ++++++++++++++-----
>  1 file changed, 14 insertions(+), 5 deletions(-)
> 
> diff --git a/newlib/libc/stdlib/nano-mallocr.c b/newlib/libc/stdlib/nano-mallocr.c
> index b2273ba60..a2b50facc 100644
> --- a/newlib/libc/stdlib/nano-mallocr.c
> +++ b/newlib/libc/stdlib/nano-mallocr.c
> @@ -333,14 +333,23 @@ void * nano_malloc(RARG malloc_size_t s)
>                 {
>                     p->size += alloc_size;
>  
> -                   /* Remove chunk from free_list */
> +                   /* Remove chunk from free_list. Since p != NULL there is
> +                      at least one chunk */
>                     r = free_list;
> -                   while (r && p != r->next)
> +                   if (r->next == NULL)
>                     {
> -                     r = r->next;
> +                       /* There is only a single chunk, remove it */
> +                       free_list = NULL;
> +                   }
> +                   else
> +                   {
> +                       /* Search for the chunk before the one to be removed */
> +                       while (p != r->next)
> +                       {
> +                           r = r->next;
> +                       }
> +                       r->next = NULL;
>                     }
> -                   r->next = NULL;
> -
>                     r = p;
>                 }
>                 else
> -- 
> 2.34.1
>
Any comment on this patch?

BR,
Henrik