alsdec: validate time diff index

If begin is smaller than t, the subtraction 'begin -= t' wraps around,
because begin is unsigned. The same applies for end < t.

This causes segmentation faults.

Signed-off-by: Andreas Cadhalpun <Andreas.Cadhalpun@googlemail.com>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
(cherry picked from commit faf9fe2c224ea81a98afd53e2f0be0a2e13aeca9)

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

1 files changed, 8 insertions, 0 deletions

diff --git a/libavcodec/alsdec.c b/libavcodec/alsdec.c
index abced6126d..d557759142 100644
--- a/libavcodec/alsdec.c
+++ b/libavcodec/alsdec.c
@@ -1286,8 +1286,16 @@ static int revert_channel_correlation(ALSDecContext *ctx, ALSBlockData *bd,
 
             if (ch[dep].time_diff_sign) {
                 t      = -t;
+                if (t > 0 && begin < t) {
+                    av_log(ctx->avctx, AV_LOG_ERROR, "begin %u smaller than time diff index %d.\n", begin, t);
+                    return AVERROR_INVALIDDATA;
+                }
                 begin -= t;
             } else {
+                if (t > 0 && end < t) {
+                    av_log(ctx->avctx, AV_LOG_ERROR, "end %u smaller than time diff index %d.\n", end, t);
+                    return AVERROR_INVALIDDATA;
+                }
                 end   -= t;
             }