[FFmpeg-cvslog] avcodec/ac3dec: Check expacc

[Michael Niedermayer]

ffmpeg | branch: master | Michael Niedermayer <michael at niedermayer.cc> | Thu Nov  3 11:30:50 2016 +0100| [cee1f4c06986941bd31cc19f4333d436394aa6f9] | committer: Michael Niedermayer

avcodec/ac3dec: Check expacc

this is somewhat a magic number, which can be understood from reading section
"7.1.2 Exponent Strategy" of the ac3 specification, in short:
Three exponents each represented as number 0-4 are grouped together and
base-5 encoded, so the maximal correct value is 25*4 + 5*4 + 4 = 124.

Reviewed-by: Andreas Cadhalpun <andreas.cadhalpun at googlemail.com>
Signed-off-by: Michael Niedermayer <michael at niedermayer.cc>

> http://git.videolan.org/gitweb.cgi/ffmpeg.git/?a=commit;h=cee1f4c06986941bd31cc19f4333d436394aa6f9
---

 libavcodec/ac3dec.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/libavcodec/ac3dec.c b/libavcodec/ac3dec.c
index a95c204..499971a 100644
--- a/libavcodec/ac3dec.c
+++ b/libavcodec/ac3dec.c
@@ -426,6 +426,10 @@ static int decode_exponents(AC3DecodeContext *s,
     group_size = exp_strategy + (exp_strategy == EXP_D45);
     for (grp = 0, i = 0; grp < ngrps; grp++) {
         expacc = get_bits(gbc, 7);
+        if (expacc >= 125) {
+            av_log(s->avctx, AV_LOG_ERROR, "expacc %d is out-of-range\n", expacc);
+            return AVERROR_INVALIDDATA;
+        }
         dexp[i++] = ungroup_3_in_7_bits_tab[expacc][0];
         dexp[i++] = ungroup_3_in_7_bits_tab[expacc][1];
         dexp[i++] = ungroup_3_in_7_bits_tab[expacc][2];