Re: [Qemu-devel] [PATCH for-2.0 06/47] block/cloop: refuse images with bogus offsets (CVE-2014-0144)

[Max Reitz <mreitz@redhat.com>]

On 26.03.2014 13:05, Stefan Hajnoczi wrote:
> The offsets[] array allows efficient seeking and tells us the maximum
> compressed data size.  If the offsets are bogus the maximum compressed
> data size will be unrealistic.
>
> This could cause g_malloc() to abort and bogus offsets mean the image is
> broken anyway.  Therefore we should refuse such images.
>
> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
> ---
>   block/cloop.c              | 34 +++++++++++++++++++++++++++++-----
>   tests/qemu-iotests/075     | 15 +++++++++++++++
>   tests/qemu-iotests/075.out |  8 ++++++++
>   3 files changed, 52 insertions(+), 5 deletions(-)
>
> diff --git a/block/cloop.c b/block/cloop.c
> index 844665e..55a804f 100644
> --- a/block/cloop.c
> +++ b/block/cloop.c
> @@ -124,12 +124,36 @@ static int cloop_open(BlockDriverState *bs, QDict *options, int flags,
>       }
>   
>       for(i=0;i<s->n_blocks;i++) {
> +        uint64_t size;
> +
>           s->offsets[i] = be64_to_cpu(s->offsets[i]);
> -        if (i > 0) {
> -            uint32_t size = s->offsets[i] - s->offsets[i - 1];
> -            if (size > max_compressed_block_size) {
> -                max_compressed_block_size = size;
> -            }
> +        if (i == 0) {
> +            continue;
> +        }
> +
> +        if (s->offsets[i] < s->offsets[i - 1]) {
> +            error_setg(errp, "offsets not monotonically increasing at "
> +                       "index %u, image file is corrupt", i);

PRIu32

> +            ret = -EINVAL;
> +            goto fail;
> +        }
> +
> +        size = s->offsets[i] - s->offsets[i - 1];
> +
> +        /* Compressed blocks should be smaller than the uncompressed block size
> +         * but maybe compression performed poorly so the compressed block is
> +         * actually bigger.  Clamp down on unrealistic values to prevent
> +         * ridiculous s->compressed_block allocation.
> +         */
> +        if (size > 2 * MAX_BLOCK_SIZE) {
> +            error_setg(errp, "invalid compressed block size at index %u, "

Okay, I'll stop. ;-)

> +                       "image file is corrupt", i);
> +            ret = -EINVAL;
> +            goto fail;
> +        }
> +
> +        if (size > max_compressed_block_size) {
> +            max_compressed_block_size = size;
>           }
>       }
>   
> diff --git a/tests/qemu-iotests/075 b/tests/qemu-iotests/075
> index 9c00fa8..d74fb33 100755
> --- a/tests/qemu-iotests/075
> +++ b/tests/qemu-iotests/075
> @@ -44,6 +44,7 @@ _supported_os Linux
>   
>   block_size_offset=128
>   n_blocks_offset=132
> +offsets_offset=136
>   
>   echo
>   echo "== check that the first sector can be read =="
> @@ -80,6 +81,20 @@ _use_sample_img simple-pattern.cloop.bz2
>   poke_file "$TEST_IMG" "$n_blocks_offset" "\x04\x00\x00\x01"
>   $QEMU_IO -c "read 0 512" $TEST_IMG 2>&1 | _filter_qemu_io | _filter_testdir
>   
> +echo
> +echo "== refuse images with non-monotonically increasing offsets =="
> +_use_sample_img simple-pattern.cloop.bz2
> +poke_file "$TEST_IMG" "$offsets_offset" "\x00\x00\x00\x00\xff\xff\xff\xff"
> +poke_file "$TEST_IMG" $((offsets_offset + 8)) "\x00\x00\x00\x00\xff\xfe\x00\x00"
> +$QEMU_IO -c "read 0 512" $TEST_IMG 2>&1 | _filter_qemu_io | _filter_testdir
> +
> +echo
> +echo "== refuse images with invalid compressed block size =="
> +_use_sample_img simple-pattern.cloop.bz2
> +poke_file "$TEST_IMG" "$offsets_offset" "\x00\x00\x00\x00\x00\x00\x00\x00"
> +poke_file "$TEST_IMG" $((offsets_offset + 8)) "\xff\xff\xff\xff\xff\xff\xff\xff"
> +$QEMU_IO -c "read 0 512" $TEST_IMG 2>&1 | _filter_qemu_io | _filter_testdir
> +
>   # success, all done
>   echo "*** done"
>   rm -f $seq.full
> diff --git a/tests/qemu-iotests/075.out b/tests/qemu-iotests/075.out
> index 7cdaee1..911cd3b 100644
> --- a/tests/qemu-iotests/075.out
> +++ b/tests/qemu-iotests/075.out
> @@ -23,4 +23,12 @@ no file open, try 'help open'
>   == refuse images that require too many offsets ===
>   qemu-io: can't open device TEST_DIR/simple-pattern.cloop: image requires too many offsets, try increasing block size
>   no file open, try 'help open'
> +
> +== refuse images with non-monotonically increasing offsets ==
> +qemu-io: can't open device TEST_DIR/simple-pattern.cloop: offsets not monotonically increasing at index 1, image file is corrupt
> +no file open, try 'help open'
> +
> +== refuse images with invalid compressed block size ==
> +qemu-io: can't open device TEST_DIR/simple-pattern.cloop: invalid compressed block size at index 1, image file is corrupt
> +no file open, try 'help open'
>   *** done

Reviewed-by: Max Reitz <mreitz@redhat.com>