[FFmpeg-devel] [PATCH] dvbsubdec: check against buffer overreads

[Janne Grunau]

on Thu, Feb 10, 2011 at 12:39:39PM +0000, M?ns Rullg?rd wrote:
> Janne Grunau <janne-ffmpeg at jannau.net> writes:
> 
> > Signed-off-by: Janne Grunau <janne-ffmpeg at jannau.net>
> > ---
> >  libavcodec/dvbsubdec.c |   11 +++++++++--
> >  1 files changed, 9 insertions(+), 2 deletions(-)
> >
> > diff --git a/libavcodec/dvbsubdec.c b/libavcodec/dvbsubdec.c
> > index 401144f..c06c017 100644
> > --- a/libavcodec/dvbsubdec.c
> > +++ b/libavcodec/dvbsubdec.c
> > @@ -1423,13 +1423,15 @@ static int dvbsub_decode(AVCodecContext *avctx,
> >
> >  #endif
> >
> > -    if (buf_size <= 2 || *buf != 0x0f)
> > +    if (buf_size <= 6 || *buf != 0x0f) {
> > +        av_dlog(avctx, "incomplete or broken packet");
> >          return -1;
> > +    }
> >
> >      p = buf;
> >      p_end = buf + buf_size;
> >
> > -    while (p < p_end && *p == 0x0f) {
> > +    while (p_end - p < 6 && *p == 0x0f) {
> 
> Err, > 6, no?

sigh, yes. >= 6 even although a segment length of 0 is probably invalid.

Janne
---8<---
Signed-off-by: Janne Grunau <janne-ffmpeg at jannau.net>
---
 libavcodec/dvbsubdec.c |   11 +++++++++--
 1 files changed, 9 insertions(+), 2 deletions(-)

diff --git a/libavcodec/dvbsubdec.c b/libavcodec/dvbsubdec.c
index 401144f..4573713 100644
--- a/libavcodec/dvbsubdec.c
+++ b/libavcodec/dvbsubdec.c
@@ -1423,13 +1423,15 @@ static int dvbsub_decode(AVCodecContext *avctx,
 
 #endif
 
-    if (buf_size <= 2 || *buf != 0x0f)
+    if (buf_size <= 6 || *buf != 0x0f) {
+        av_dlog(avctx, "incomplete or broken packet");
         return -1;
+    }
 
     p = buf;
     p_end = buf + buf_size;
 
-    while (p < p_end && *p == 0x0f) {
+    while (p_end - p >= 6 && *p == 0x0f) {
         p += 1;
         segment_type = *p++;
         page_id = AV_RB16(p);
@@ -1437,6 +1439,11 @@ static int dvbsub_decode(AVCodecContext *avctx,
         segment_length = AV_RB16(p);
         p += 2;
 
+        if (p_end - p < segment_length) {
+            av_dlog(avctx, "incomplete or broken packet");
+            return -1;
+        }
+
         if (page_id == ctx->composition_id || page_id == ctx->ancillary_id ||
             ctx->composition_id == -1 || ctx->ancillary_id == -1) {
             switch (segment_type) {
-- 
1.7.4