avcodec/pnm: Use ff_set_dimensions()

Fixes: OOM
Fixes: 1906/clusterfuzz-testcase-minimized-4599315114754048

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpegSigned-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavcodec/pnm.c

@@ -24,6 +24,7 @@
 
 #include "libavutil/imgutils.h"
 #include "avcodec.h"
+#include "internal.h"
 #include "pnm.h"
 
 static inline int pnm_space(int c)
@@ -61,6 +62,7 @@ int ff_pnm_decode_header(AVCodecContext *avctx, PNMContext * const s)
 {
     char buf1[32], tuple_type[32];
     int h, w, depth, maxval;
+    int ret;
 
     pnm_get(s, buf1, sizeof(buf1));
     if(buf1[0] != 'P')
@@ -111,8 +113,9 @@ int ff_pnm_decode_header(AVCodecContext *avctx, PNMContext * const s)
             av_image_check_size(w, h, 0, avctx) || s->bytestream >= s->bytestream_end)
             return AVERROR_INVALIDDATA;
 
-        avctx->width  = w;
-        avctx->height = h;
+        ret = ff_set_dimensions(avctx, w, h);
+        if (ret < 0)
+            return ret;
         s->maxval     = maxval;
         if (depth == 1) {
             if (maxval == 1) {
@@ -154,8 +157,9 @@ int ff_pnm_decode_header(AVCodecContext *avctx, PNMContext * const s)
     if(w <= 0 || h <= 0 || av_image_check_size(w, h, 0, avctx) || s->bytestream >= s->bytestream_end)
         return AVERROR_INVALIDDATA;
 
-    avctx->width  = w;
-    avctx->height = h;
+    ret = ff_set_dimensions(avctx, w, h);
+    if (ret < 0)
+        return ret;
 
     if (avctx->pix_fmt != AV_PIX_FMT_MONOWHITE && avctx->pix_fmt != AV_PIX_FMT_MONOBLACK) {
         pnm_get(s, buf1, sizeof(buf1));