[FFmpeg-devel] [PATCH]Fix progressive jpgs with weird pix_fmts

[Carl Eugen Hoyos]

Hi!

On Saturday 07 January 2012 03:27:52 am Michael Niedermayer wrote:
> On Sat, Jan 07, 2012 at 03:17:36AM +0100, Carl Eugen Hoyos wrote:
> > On Saturday 07 January 2012 02:59:06 am Michael Niedermayer wrote:
> > > > Attached fixes the samples from ticket #892 for me.
> > > >
> > > > Please comment, Carl Eugen
> > >
> > > reset upscale* otherwise this is possibly exploitable if the width or
> > > height or "pix_fmt" changes
> >
> > As in attached?
> 
> not enough
> 
> 1st frame sets upscale_h
> 2nd frame changes width/height and branches via -1 from
>  ff_mjpeg_find_marker to the_end

Iiuc, width/height can only be set in ff_mjpeg_decode_sof(), so new patch 
resets the value at the beginning of this function.

> also wherever the variables are reset i suggest that a av_assert0 is
> added to make sure the pixel format matches the expectation that is
> theres enough space for chroma

I don't understand:
If the variables are reset (to 0), the code that may overwrite chroma / 
corrupt memory is not called, the variables are set together with the pix_fmt.

Only s->ls change the pix_fmt later, upscale now also gets reset in this case.

New patch attached, Carl Eugen
-------------- next part --------------
diff --git a/libavcodec/mjpegdec.c b/libavcodec/mjpegdec.c
index 58bbd63..8c2cc6b 100644
--- a/libavcodec/mjpegdec.c
+++ b/libavcodec/mjpegdec.c
@@ -217,6 +217,7 @@ int ff_mjpeg_decode_sof(MJpegDecodeContext *s)
     int len, nb_components, i, width, height, pix_fmt_id;
 
     s->cur_scan = 0;
+    s->upscale_h = s->upscale_v = 0;
 
     /* XXX: verify len field validity */
     len = get_bits(&s->gb, 16);
@@ -393,6 +394,7 @@ int ff_mjpeg_decode_sof(MJpegDecodeContext *s)
         return -1;
     }
     if(s->ls){
+        s->upscale_h = s->upscale_v = 0;
         if(s->nb_components > 1)
             s->avctx->pix_fmt = PIX_FMT_RGB24;
         else if(s->bits <= 8)
@@ -1173,28 +1175,6 @@ int ff_mjpeg_decode_sos(MJpegDecodeContext *s,
                 return -1;
         }
     }
-    if (s->upscale_h) {
-        uint8_t *line = s->picture_ptr->data[s->upscale_h];
-        for (i = 0; i < s->chroma_height; i++) {
-            for (index = s->width - 1; index; index--)
-                line[index] = (line[index / 2] + line[(index + 1) / 2]) >> 1;
-            line += s->linesize[s->upscale_h];
-        }
-    }
-    if (s->upscale_v) {
-        uint8_t *dst = &((uint8_t *)s->picture_ptr->data[s->upscale_v])[(s->height - 1) * s->linesize[s->upscale_v]];
-        for (i = s->height - 1; i; i--) {
-            uint8_t *src1 = &((uint8_t *)s->picture_ptr->data[s->upscale_v])[i / 2 * s->linesize[s->upscale_v]];
-            uint8_t *src2 = &((uint8_t *)s->picture_ptr->data[s->upscale_v])[(i + 1) / 2 * s->linesize[s->upscale_v]];
-            if (src1 == src2) {
-                memcpy(dst, src1, s->width);
-            } else {
-                for (index = 0; index < s->width; index++)
-                    dst[index] = (src1[index] + src2[index]) >> 1;
-            }
-            dst -= s->linesize[s->upscale_v];
-        }
-    }
     emms_c();
     return 0;
  out_of_range:
@@ -1524,7 +1504,7 @@ int ff_mjpeg_decode_frame(AVCodecContext *avctx,
                               AVPacket *avpkt)
 {
     const uint8_t *buf = avpkt->data;
-    int buf_size = avpkt->size;
+    int i, index, buf_size = avpkt->size;
     MJpegDecodeContext *s = avctx->priv_data;
     const uint8_t *buf_end, *buf_ptr;
     const uint8_t *unescaped_buf_ptr;
@@ -1683,6 +1663,28 @@ eoi_parser:
     av_log(avctx, AV_LOG_FATAL, "No JPEG data found in image\n");
     return -1;
 the_end:
+    if (s->upscale_h) {
+        uint8_t *line = s->picture_ptr->data[s->upscale_h];
+        for (i = 0; i < s->chroma_height; i++) {
+            for (index = s->width - 1; index; index--)
+                line[index] = (line[index / 2] + line[(index + 1) / 2]) >> 1;
+            line += s->linesize[s->upscale_h];
+        }
+    }
+    if (s->upscale_v) {
+        uint8_t *dst = &((uint8_t *)s->picture_ptr->data[s->upscale_v])[(s->height - 1) * s->linesize[s->upscale_v]];
+        for (i = s->height - 1; i; i--) {
+            uint8_t *src1 = &((uint8_t *)s->picture_ptr->data[s->upscale_v])[i / 2 * s->linesize[s->upscale_v]];
+            uint8_t *src2 = &((uint8_t *)s->picture_ptr->data[s->upscale_v])[(i + 1) / 2 * s->linesize[s->upscale_v]];
+            if (src1 == src2) {
+                memcpy(dst, src1, s->width);
+            } else {
+                for (index = 0; index < s->width; index++)
+                    dst[index] = (src1[index] + src2[index]) >> 1;
+            }
+            dst -= s->linesize[s->upscale_v];
+        }
+    }
     av_log(avctx, AV_LOG_DEBUG, "mjpeg decode frame unused %td bytes\n", buf_end - buf_ptr);
 //    return buf_end - buf_ptr;
     return buf_ptr - buf;