[FFmpeg-devel] [PATCH] Check return value from avio_read() to verify data actually read

[Michael Niedermayer]

On Mon, Mar 23, 2020 at 05:52:01PM -0700, John Rummell wrote:
> Chromium fuzzers have caught places where uninitialized data was used due
> to calls to avio_read() not verifying that the number of bytes expected was
> actually read. So updating the code to check the result from avio_read().

>  mov.c    |   26 ++++++++++++++++++--------
>  oggdec.c |    3 ++-
>  wavdec.c |   12 ++++++++----
>  3 files changed, 28 insertions(+), 13 deletions(-)
> 66938bc5adfc7d151b376f6d396c4a0dc7f97a4c  0001-Check-return-value-from-avio_read-to-verify-data-act.patch
> From 7f80d50711486a4b923bd8d1e26abc9649d570e3 Mon Sep 17 00:00:00 2001
> From: John Rummell <jrummell at chromium.org>
> Date: Mon, 23 Mar 2020 15:48:33 -0700
> Subject: [PATCH] Check return value from avio_read() to verify data actually
>  read
> 
> If the buffer doesn't contain enough bytes when reading a stream,
> fail rather than continuing on with unitialized data. One attempt
> caught by Chromium fuzzers (crbug.com/1054229), rest done by looking
> for calls to avio_read() that don't check the result in Chromium
> code search.
> ---
>  libavformat/mov.c    | 26 ++++++++++++++++++--------
>  libavformat/oggdec.c |  3 ++-
>  libavformat/wavdec.c | 12 ++++++++----
>  3 files changed, 28 insertions(+), 13 deletions(-)
> 
> diff --git a/libavformat/mov.c b/libavformat/mov.c
> index f280f360b6..a5b4d04e37 100644
> --- a/libavformat/mov.c
> +++ b/libavformat/mov.c
> @@ -1012,10 +1012,16 @@ static int mov_read_adrm(MOVContext *c, AVIOContext *pb, MOVAtom atom)
>      }
>  
>      /* drm blob processing */
> -    avio_read(pb, output, 8); // go to offset 8, absolute position 0x251
> -    avio_read(pb, input, DRM_BLOB_SIZE);
> -    avio_read(pb, output, 4); // go to offset 4, absolute position 0x28d
> -    avio_read(pb, file_checksum, 20);
> +    /* go to offset 8, absolute position 0x251 */
> +    if ((ret = avio_read(pb, output, 8)) != 8)
> +        goto fail;
> +    if ((ret = avio_read(pb, input, DRM_BLOB_SIZE)) != DRM_BLOB_SIZE)
> +        goto fail;
> +    /* go to offset 4, absolute position 0x28d */
> +    if ((ret = avio_read(pb, output, 4)) != 4)
> +        goto fail;
> +    if ((ret = avio_read(pb, file_checksum, 20)) != 20)
> +        goto fail;

These would cause mov_read_adrm() to fail but not neccessarily return an
error code if any of these reads less.
Is that intended ?

thx

[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Complexity theory is the science of finding the exact solution to an
approximation. Benchmarking OTOH is finding an approximation of the exact
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