[FFmpeg-devel] [PATCH 1/3] nutdec: fix illegal count check in decode_main_header

[Andreas Cadhalpun]

The existing check has two problems:
 1) i + count can overflow, so that the check '< 256' returns true.
 2) In the (i == 'N') case occurs a j-- so that the loop runs once more.

This can trigger the assertion 'nut->header_len[0] == 0' or cause
segmentation faults or infinite hangs.

Signed-off-by: Andreas Cadhalpun <Andreas.Cadhalpun at googlemail.com>
---
 libavformat/nutdec.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/libavformat/nutdec.c b/libavformat/nutdec.c
index 1bb2091..46946d3 100644
--- a/libavformat/nutdec.c
+++ b/libavformat/nutdec.c
@@ -294,7 +294,7 @@ static int decode_main_header(NUTContext *nut)
         while (tmp_fields-- > 8)
             ffio_read_varlen(bc);
 
-        if (count == 0 || i + count > 256) {
+        if (count <= 0 || (i > 'N' && count > 256 - i) || (i <= 'N' && count > 255 - i)) {
             av_log(s, AV_LOG_ERROR, "illegal count %d at %d\n", count, i);
             return AVERROR_INVALIDDATA;
         }
-- 
2.1.4