[FFmpeg-devel] [PATCH] avcodec/adpcm: fix heap-buffer-overflow in IMA MAGIX decoding

[Ard Biesheuvel via ffmpeg-devel <ffmpeg-devel@ffmpeg.org>]

From: Ard Biesheuvel <ardb@google.com>

The IMA MAGIX decoder calculates the output buffer size (nb_samples)
based on the actual input packet size (buf_size) via get_nb_samples().
However, the decoding loop previously relied on avctx->block_align to
determine the iteration count.

When block_align is larger than the actual packet size (e.g., a 71-byte
packet with block_align=16384), the loop attempts to process more data
than available. This results in out-of-bounds reads from the input
bytestream and out-of-bounds writes to the allocated output buffer.

Fix this by adding a check for remaining input bytes (>= 8) to the loop
condition, ensuring the loop terminates when the input is exhausted.

oss-fuzz: https://oss-fuzz.com/testcase-detail/4847227777646592
Co-authored-by: CodeMender <codemender-patching@google.com>
Signed-off-by: Ard Biesheuvel <ardb@google.com>
---
 libavcodec/adpcm.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/libavcodec/adpcm.c b/libavcodec/adpcm.c
index bd9ad2933f..2828cb8c31 100644
--- a/libavcodec/adpcm.c
+++ b/libavcodec/adpcm.c
@@ -1799,7 +1799,7 @@ static int adpcm_decode_frame(AVCodecContext *avctx, AVFrame *frame,
             }
         }
 
-        for (int m = 0; m < avctx->block_align-8; m += 8) {
+        for (int m = 0; m < avctx->block_align-8 && bytestream2_get_bytes_left(&gb) >= 8; m += 8) {
             uint32_t v0 = bytestream2_get_le32u(&gb);
             uint32_t v1 = bytestream2_get_le32u(&gb);
 
-- 
2.53.0.239.g8d8fc8a987-goog

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