[FFmpeg-cvslog] avcodec/wmalosslessdec: fix overflow with pred in revert_cdlms

[Michael Niedermayer]

ffmpeg | branch: release/4.2 | Michael Niedermayer <michael at niedermayer.cc> | Sun Jun 28 00:10:19 2020 +0200| [e02303282d5098c725ca710987ed2b79ef93eb5d] | committer: Michael Niedermayer

avcodec/wmalosslessdec: fix overflow with pred in revert_cdlms

Fixes: signed integer overflow: 2048 + 2147483646 cannot be represented in type 'int'
Fixes: 23538/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_WMALOSSLESS_fuzzer-5227567073460224

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
Signed-off-by: Michael Niedermayer <michael at niedermayer.cc>
(cherry picked from commit 21598d711d894081d0566282473044ba4f378f33)
Signed-off-by: Michael Niedermayer <michael at niedermayer.cc>

> http://git.videolan.org/gitweb.cgi/ffmpeg.git/?a=commit;h=e02303282d5098c725ca710987ed2b79ef93eb5d
---

 libavcodec/wmalosslessdec.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/libavcodec/wmalosslessdec.c b/libavcodec/wmalosslessdec.c
index 7251bc0d32..2228eecd96 100644
--- a/libavcodec/wmalosslessdec.c
+++ b/libavcodec/wmalosslessdec.c
@@ -761,7 +761,8 @@ static void lms_update ## bits (WmallDecodeCtx *s, int ich, int ilms, int input)
 static void revert_cdlms ## bits (WmallDecodeCtx *s, int ch, \
                                   int coef_begin, int coef_end) \
 { \
-    int icoef, pred, ilms, num_lms, residue, input; \
+    int icoef, ilms, num_lms, residue, input; \
+    unsigned pred;\
  \
     num_lms = s->cdlms_ttl[ch]; \
     for (ilms = num_lms - 1; ilms >= 0; ilms--) { \
@@ -775,7 +776,7 @@ static void revert_cdlms ## bits (WmallDecodeCtx *s, int ch, \
                                                         s->cdlms[ch][ilms].recent, \
                                                         FFALIGN(s->cdlms[ch][ilms].order, ROUND), \
                                                         WMASIGN(residue)); \
-            input = residue + (unsigned)(pred >> s->cdlms[ch][ilms].scaling); \
+            input = residue + (unsigned)((int)pred >> s->cdlms[ch][ilms].scaling); \
             lms_update ## bits(s, ch, ilms, input); \
             s->channel_residues[ch][icoef] = input; \
         } \