[FFmpeg-devel] [PATCH 3/3] avcodec/mlpdec: Check quant_step_size against huff_lsbs

[Michael Niedermayer]

This reorders the operations so as to avoid computations with the above arguments
before they have been initialized.
Fixes part of 1708/clusterfuzz-testcase-minimized-5035111957397504

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/targets/ffmpeg
Signed-off-by: Michael Niedermayer <michael at niedermayer.cc>
---
 libavcodec/mlpdec.c | 34 +++++++++++++++++++++++++---------
 1 file changed, 25 insertions(+), 9 deletions(-)

diff --git a/libavcodec/mlpdec.c b/libavcodec/mlpdec.c
index c0a23c5f0d..11be380d27 100644
--- a/libavcodec/mlpdec.c
+++ b/libavcodec/mlpdec.c
@@ -825,8 +825,6 @@ static int read_channel_params(MLPDecodeContext *m, unsigned int substr,
         return AVERROR_INVALIDDATA;
     }
 
-    cp->sign_huff_offset = calculate_sign_huff(m, substr, ch);
-
     return 0;
 }
 
@@ -838,7 +836,8 @@ static int read_decoding_params(MLPDecodeContext *m, GetBitContext *gbp,
 {
     SubStream *s = &m->substream[substr];
     unsigned int ch;
-    int ret;
+    int ret = 0;
+    unsigned recompute_sho = 0;
 
     if (s->param_presence_flags & PARAM_PRESENCE)
         if (get_bits1(gbp))
@@ -878,19 +877,36 @@ static int read_decoding_params(MLPDecodeContext *m, GetBitContext *gbp,
     if (s->param_presence_flags & PARAM_QUANTSTEP)
         if (get_bits1(gbp))
             for (ch = 0; ch <= s->max_channel; ch++) {
-                ChannelParams *cp = &s->channel_params[ch];
-
                 s->quant_step_size[ch] = get_bits(gbp, 4);
 
-                cp->sign_huff_offset = calculate_sign_huff(m, substr, ch);
+                recompute_sho |= 1<<ch;
             }
 
     for (ch = s->min_channel; ch <= s->max_channel; ch++)
-        if (get_bits1(gbp))
+        if (get_bits1(gbp)) {
+            recompute_sho |= 1<<ch;
             if ((ret = read_channel_params(m, substr, gbp, ch)) < 0)
-                return ret;
+                goto fail;
+        }
 
-    return 0;
+
+fail:
+    for (ch = 0; ch <= s->max_channel; ch++) {
+        if (recompute_sho & (1<<ch)) {
+            ChannelParams *cp = &s->channel_params[ch];
+
+            if (cp->codebook > 0 && cp->huff_lsbs < s->quant_step_size[ch]) {
+                if (ret >= 0) {
+                    av_log(m->avctx, AV_LOG_ERROR, "quant_step_size larger than huff_lsbs\n");
+                    ret = AVERROR_INVALIDDATA;
+                }
+                s->quant_step_size[ch] = 0;
+            }
+
+            cp->sign_huff_offset = calculate_sign_huff(m, substr, ch);
+        }
+    }
+    return ret;
 }
 
 #define MSB_MASK(bits)  (-1u << (bits))
-- 
2.13.0