[FFmpeg-devel] [PATCH] [RFC] PNG: decode textual data

[Nicolas George]

Le decadi 30 ventôse, an CCXIX, Nicolas George a écrit :
> +        rbuf = av_realloc(buf, out_size + 1);
> +        if (!rbuf) {
> +            av_free(buf);
> +            return -1;
> +        }

By the way: I see a lot of realloc-related potential memory leaks in the
code. Some things like that:

        vlc->table = av_realloc(vlc->table,
                                sizeof(VLC_TYPE) * 2 * vlc->table_allocated);
        if (!vlc->table)
            return -1;

realloc failures are very unlikely, but that should not be a reason not to
do thing properly, and that requires code. Therefore, it may be useful to
introduce the following function:

/**
 * Allocate or reallocate a block of memory.
 * This function does the same thing as av_realloc, except:
 * - It takes two arguments and checks the result of the multiplication for
 *   integer overflow.
 * - It frees the input block in case of failure, thus avoiding the memory
 *   leak with the classic "buf = realloc(buf); if (!buf) return -1;".
 */
void *av_realloc_f(void *ptr, size_t nelem, size_t elsize)
{
    size_t size = nelem * elsize;
    void *r;

    /* Hack inspired from glibc: only try the division if nelem and elsize
     * are both greater than sqrt(SIZE_MAX). */
    if ((nelem | elsize) >= ((size_t)1 << (sizeof(size_t) * 4)) &&
        elsize && size / elsize != nelem) {
        av_free(ptr);
        return NULL;
    }
    r = av_realloc(ptr, size);
    if (!r && size)
        av_free(ptr);
    return r;
}

I'll also try to see if I can come up with a nice interface for the scheme I
used in png_decode_zbuf: start with a small buffer on the stack, enlarge it
on the heap if necessary.

Regards,

-- 
  Nicolas George
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