avfilter/vf_unsharp: Don't dereference NULL

The unsharp filter uses an array of arrays of uint32_t, each of which is
separately allocated. These arrays also need to freed separately; but
before doing so, one needs to check whether the array of arrays has
actually been allocated, otherwise one would dereference a NULL pointer.
This fixes #8408.

Furthermore, the array of arrays needs to be zero-initialized so that
no uninitialized pointer will be freed in case an allocation of one of
the individual arrays fails.

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
Reviewed-by: Paul B Mahol <onemda@gmail.com>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavfilter/vf_unsharp.c

@@ -218,7 +218,7 @@ static int init_filter_param(AVFilterContext *ctx, UnsharpFilterParam *fp, const
            effect, effect_type, fp->msize_x, fp->msize_y, fp->amount / 65535.0);
 
     fp->sr = av_malloc_array((MAX_MATRIX_SIZE - 1) * s->nb_threads, sizeof(uint32_t));
-    fp->sc = av_malloc_array(2 * fp->steps_y * s->nb_threads, sizeof(uint32_t **));
+    fp->sc = av_mallocz_array(2 * fp->steps_y * s->nb_threads, sizeof(uint32_t *));
     if (!fp->sr || !fp->sc)
         return AVERROR(ENOMEM);
 
@@ -258,9 +258,11 @@ static void free_filter_param(UnsharpFilterParam *fp, int nb_threads)
 {
     int z;
 
-    for (z = 0; z < 2 * fp->steps_y * nb_threads; z++)
-        av_freep(&fp->sc[z]);
-    av_freep(&fp->sc);
+    if (fp->sc) {
+        for (z = 0; z < 2 * fp->steps_y * nb_threads; z++)
+            av_freep(&fp->sc[z]);
+        av_freep(&fp->sc);
+    }
     av_freep(&fp->sr);
 }