Re: [PATCH 1/2] malloc: fix an over-allocation bug

[Rich Felker <dalias@libc.org>]

On Mon, Apr 16, 2018 at 08:54:35PM +0300, Alexander Monakov wrote:
> Fix an instance where realloc code would overallocate by OVERHEAD bytes
> amount. Manually arrange for reuse of memcpy-free-return exit sequence.
> ---
>  src/malloc/malloc.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/src/malloc/malloc.c b/src/malloc/malloc.c
> index 9e05e1d6..1af4ae5a 100644
> --- a/src/malloc/malloc.c
> +++ b/src/malloc/malloc.c
> @@ -397,10 +397,9 @@ void *realloc(void *p, size_t n)
>  		size_t newlen = n + extra;
>  		/* Crash on realloc of freed chunk */
>  		if (extra & 1) a_crash();
> -		if (newlen < PAGE_SIZE && (new = malloc(n))) {
> -			memcpy(new, p, n-OVERHEAD);
> -			free(p);
> -			return new;
> +		if (newlen < PAGE_SIZE && (new = malloc(n-OVERHEAD))) {
> +			n0 = n;
> +			goto copy_free_ret;
>  		}
>  		newlen = (newlen + PAGE_SIZE-1) & -PAGE_SIZE;
>  		if (oldlen == newlen) return p;
> @@ -443,6 +442,7 @@ copy_realloc:
>  	/* As a last resort, allocate a new chunk and copy to it. */
>  	new = malloc(n-OVERHEAD);
>  	if (!new) return 0;
> +copy_free_ret:
>  	memcpy(new, p, n0-OVERHEAD);
>  	free(CHUNK_TO_MEM(self));
>  	return new;

Looks ok. I've got this queued as submitted.

Rich