Re: [Qemu-devel] [PATCH 5/5] qcow1: Stricter backing file length check*

["Benoît Canet" <benoit.canet@irqsave.net>]

The Monday 12 May 2014 à 15:04:11 (+0200), Kevin Wolf wrote :
> Like qcow2 since commit 6d33e8e7, error out on invalid lengths instead
> of silently truncating them to 1023.
> 
> Also don't rely on bdrv_pread() catching integer overflows that make len
> negative, but use unsigned variables in the first place.
> 
> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
> ---
>  block/qcow.c               |  7 +++++--
>  tests/qemu-iotests/092     | 11 +++++++++++
>  tests/qemu-iotests/092.out |  7 +++++++
>  3 files changed, 23 insertions(+), 2 deletions(-)
> 
> diff --git a/block/qcow.c b/block/qcow.c
> index 3566c05..7fd57d7 100644
> --- a/block/qcow.c
> +++ b/block/qcow.c
> @@ -97,7 +97,8 @@ static int qcow_open(BlockDriverState *bs, QDict *options, int flags,
>                       Error **errp)
>  {
>      BDRVQcowState *s = bs->opaque;
> -    int len, i, shift, ret;
> +    unsigned int len, i, shift;
> +    int ret;
>      QCowHeader header;
>  
>      ret = bdrv_pread(bs->file, 0, &header, sizeof(header));
> @@ -202,7 +203,9 @@ static int qcow_open(BlockDriverState *bs, QDict *options, int flags,
>      if (header.backing_file_offset != 0) {
>          len = header.backing_file_size;
>          if (len > 1023) {
> -            len = 1023;
> +            error_setg(errp, "Backing file name too long");
> +            ret = -EINVAL;
> +            goto fail;
>          }
>          ret = bdrv_pread(bs->file, header.backing_file_offset,
>                     bs->backing_file, len);
> diff --git a/tests/qemu-iotests/092 b/tests/qemu-iotests/092
> index 26a1324..b1333a0 100755
> --- a/tests/qemu-iotests/092
> +++ b/tests/qemu-iotests/092
> @@ -43,6 +43,8 @@ _supported_fmt qcow
>  _supported_proto generic
>  _supported_os Linux
>  
> +offset_backing_file_offset=8
> +offset_backing_file_size=16
>  offset_size=24
>  offset_cluster_bits=32
>  offset_l2_bits=33
> @@ -73,6 +75,15 @@ poke_file "$TEST_IMG" "$offset_size" "\xee\xee\xee\xee\xee\xee\xee\xee"
>  poke_file "$TEST_IMG" "$offset_size" "\x7f\xff\xff\xff\xff\xff\xff\xff"
>  { $QEMU_IO -c "write 0 64M" $TEST_IMG; } 2>&1 | _filter_qemu_io | _filter_testdir
>  
> +echo
> +echo "== Invalid backing file length =="
> +_make_test_img 64M
> +poke_file "$TEST_IMG" "$offset_backing_file_offset" "\x00\x00\x00\xff"
> +poke_file "$TEST_IMG" "$offset_backing_file_size" "\xff\xff\xff\xff"
> +{ $QEMU_IO -c "read 0 512" $TEST_IMG; } 2>&1 | _filter_qemu_io | _filter_testdir
> +poke_file "$TEST_IMG" "$offset_backing_file_size" "\x7f\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/092.out b/tests/qemu-iotests/092.out
> index c3678a0..e957887 100644
> --- a/tests/qemu-iotests/092.out
> +++ b/tests/qemu-iotests/092.out
> @@ -20,4 +20,11 @@ qemu-io: can't open device TEST_DIR/t.qcow: Image too large
>  no file open, try 'help open'
>  qemu-io: can't open device TEST_DIR/t.qcow: Image too large
>  no file open, try 'help open'
> +
> +== Invalid backing file length ==
> +Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=67108864 
> +qemu-io: can't open device TEST_DIR/t.qcow: Backing file name too long
> +no file open, try 'help open'
> +qemu-io: can't open device TEST_DIR/t.qcow: Backing file name too long
> +no file open, try 'help open'
>  *** done
> -- 
> 1.8.3.1
> 
> 
Reviewed-by: Benoit Canet <benoit@irqsave.net>