[FFmpeg-cvslog] avcodec/dirac_arith: Treat overread as error

[Michael Niedermayer]

ffmpeg | branch: master | Michael Niedermayer <michael at niedermayer.cc> | Tue Jan  8 23:40:54 2019 +0100| [51978aefe8074cc3e020994f6b329387b2149cb8] | committer: Michael Niedermayer

avcodec/dirac_arith: Treat overread as error

Fixes: Timeout
Fixes: 11663/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_DIRAC_fuzzer-5636791864918016

Before:Executed clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_DIRAC_fuzzer-5636791864918016 in 26006 ms
After: Executed clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_DIRAC_fuzzer-5636791864918016 in 106 ms

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

> http://git.videolan.org/gitweb.cgi/ffmpeg.git/?a=commit;h=51978aefe8074cc3e020994f6b329387b2149cb8
---

 libavcodec/dirac_arith.c | 1 +
 libavcodec/dirac_arith.h | 4 ++++
 2 files changed, 5 insertions(+)

diff --git a/libavcodec/dirac_arith.c b/libavcodec/dirac_arith.c
index 1e6b964772..36142fe198 100644
--- a/libavcodec/dirac_arith.c
+++ b/libavcodec/dirac_arith.c
@@ -116,6 +116,7 @@ void ff_dirac_init_arith_decoder(DiracArith *c, GetBitContext *gb, int length)
     c->counter = -16;
     c->range   = 0xffff;
     c->error   = 0;
+    c->overread= 0;
 
     for (i = 0; i < DIRAC_CTX_COUNT; i++)
         c->contexts[i] = 0x8000;
diff --git a/libavcodec/dirac_arith.h b/libavcodec/dirac_arith.h
index efe30b79de..79526a7ca3 100644
--- a/libavcodec/dirac_arith.h
+++ b/libavcodec/dirac_arith.h
@@ -82,6 +82,7 @@ typedef struct {
 
     uint16_t contexts[DIRAC_CTX_COUNT];
     int error;
+    int overread;
 } DiracArith;
 
 extern const uint8_t ff_dirac_next_ctx[DIRAC_CTX_COUNT];
@@ -119,6 +120,9 @@ static inline void refill(DiracArith *c)
                 new |= 0xff00;
 
             c->bytestream = c->bytestream_end;
+            c->overread ++;
+            if (c->overread > 4)
+                c->error = AVERROR_INVALIDDATA;
         }
 
         c->low += new << counter;