[FFmpeg-devel] [PATCH] avcodec/dca_xll: fix use of uninitialized memory of get_rice_array() (PR #21285)

[michaelni via ffmpeg-devel <ffmpeg-devel@ffmpeg.org>]

PR #21285 opened by michaelni
URL: https://code.ffmpeg.org/FFmpeg/FFmpeg/pulls/21285
Patch URL: https://code.ffmpeg.org/FFmpeg/FFmpeg/pulls/21285.patch


>From f559146bb79277e0bb52d117516f93f7bb7ae28a Mon Sep 17 00:00:00 2001
From: Michael Niedermayer <michael@niedermayer.cc>
Date: Tue, 23 Dec 2025 16:22:23 +0100
Subject: [PATCH 1/2] avcodec/dca_xll: Check get_rice_array()

Fixes: use of uninitialized memory
Fixes: 451655450/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_DCA_DEC_fuzzer-6527248623796224

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
---
 libavcodec/dca_xll.c | 18 +++++++++++++-----
 1 file changed, 13 insertions(+), 5 deletions(-)

diff --git a/libavcodec/dca_xll.c b/libavcodec/dca_xll.c
index 0e9a4e77e7..86e992bf1c 100644
--- a/libavcodec/dca_xll.c
+++ b/libavcodec/dca_xll.c
@@ -64,12 +64,16 @@ static void get_linear_array(GetBitContext *gb, int32_t *array, int size, int n)
         array[i] = get_linear(gb, n);
 }
 
-static void get_rice_array(GetBitContext *gb, int32_t *array, int size, int k)
+static int get_rice_array(GetBitContext *gb, int32_t *array, int size, int k)
 {
     int i;
 
-    for (i = 0; i < size; i++)
+    for (i = 0; i < size && get_bits_left(gb) > k; i++)
         array[i] = get_rice(gb, k);
+
+    if (i < size)
+        return AVERROR_INVALIDDATA;
+    return 0;
 }
 
 static int parse_dmix_coeffs(DCAXllDecoder *s, DCAXllChSet *c)
@@ -529,8 +533,10 @@ static int chs_parse_band_data(DCAXllDecoder *s, DCAXllChSet *c, int band, int s
         } else {
             // Rice codes
             // Unpack all residuals of part A of segment 0
-            get_rice_array(&s->gb, part_a, c->nsamples_part_a[k],
-                           c->bitalloc_part_a[k]);
+            int ret = get_rice_array(&s->gb, part_a, c->nsamples_part_a[k],
+                                     c->bitalloc_part_a[k]);
+            if (ret < 0)
+                return ret;
 
             if (c->bitalloc_hybrid_linear[k]) {
                 // Hybrid Rice codes
@@ -560,7 +566,9 @@ static int chs_parse_band_data(DCAXllDecoder *s, DCAXllChSet *c, int band, int s
             } else {
                 // Rice codes
                 // Unpack all residuals of part B of segment 0 and others
-                get_rice_array(&s->gb, part_b, nsamples_part_b, c->bitalloc_part_b[k]);
+                ret = get_rice_array(&s->gb, part_b, nsamples_part_b, c->bitalloc_part_b[k]);
+                if (ret < 0)
+                    return ret;
             }
         }
     }
-- 
2.49.1


>From 09bdd5b7ecf2b98e5cb7e916fdcd456e521476db Mon Sep 17 00:00:00 2001
From: Michael Niedermayer <michael@niedermayer.cc>
Date: Tue, 23 Dec 2025 16:24:22 +0100
Subject: [PATCH 2/2] avcodec/dca_xll: Clear padding in pbr_buffer

The testcase is already fixed by the previous commit

Fixes: use of uninitilaized memory
Fixes: 451655450/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_DCA_DEC_fuzzer-6527248623796224

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
---
 libavcodec/dca_xll.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/libavcodec/dca_xll.c b/libavcodec/dca_xll.c
index 86e992bf1c..20ace57271 100644
--- a/libavcodec/dca_xll.c
+++ b/libavcodec/dca_xll.c
@@ -1102,6 +1102,7 @@ static int copy_to_pbr(DCAXllDecoder *s, const uint8_t *data, int size, int dela
         return AVERROR(ENOMEM);
 
     memcpy(s->pbr_buffer, data, size);
+    memset(s->pbr_buffer + size, 0, DCA_XLL_PBR_BUFFER_MAX + AV_INPUT_BUFFER_PADDING_SIZE - size);
     s->pbr_length = size;
     s->pbr_delay = delay;
     return 0;
-- 
2.49.1

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