Re: [PATCH] block: Raise an error when backing file parameter is an empty string

[Connor Kuehl <ckuehl@redhat.com>]

Hi Kevin & Max,

Just pinging this patch for your consideration.

Thank you,

Connor

On 6/17/20 11:27 AM, Connor Kuehl wrote:
> Providing an empty string for the backing file parameter like so:
> 
> 	qemu-img create -f qcow2 -b '' /tmp/foo
> 
> allows the flow of control to reach and subsequently fail an assert
> statement because passing an empty string to
> 
> 	bdrv_get_full_backing_filename_from_filename()
> 
> simply results in NULL being returned without an error being raised.
> 
> To fix this, let's check for an empty string when getting the value from
> the opts list.
> 
> Reported-by: Attila Fazekas <afazekas@redhat.com>
> Fixes: https://bugzilla.redhat.com/1809553
> Signed-off-by: Connor Kuehl <ckuehl@redhat.com>
> ---
>   block.c                    |  4 ++++
>   tests/qemu-iotests/298     | 47 ++++++++++++++++++++++++++++++++++++++
>   tests/qemu-iotests/298.out |  5 ++++
>   tests/qemu-iotests/group   |  1 +
>   4 files changed, 57 insertions(+)
>   create mode 100755 tests/qemu-iotests/298
>   create mode 100644 tests/qemu-iotests/298.out
> 
> diff --git a/block.c b/block.c
> index 6dbcb7e083..b335d6bcb2 100644
> --- a/block.c
> +++ b/block.c
> @@ -6116,6 +6116,10 @@ void bdrv_img_create(const char *filename, const char *fmt,
>                                "same filename as the backing file");
>               goto out;
>           }
> +        if (backing_file[0] == '\0') {
> +            error_setg(errp, "Expected backing file name, got empty string");
> +            goto out;
> +        }
>       }
>   
>       backing_fmt = qemu_opt_get(opts, BLOCK_OPT_BACKING_FMT);
> diff --git a/tests/qemu-iotests/298 b/tests/qemu-iotests/298
> new file mode 100755
> index 0000000000..1e30caebec
> --- /dev/null
> +++ b/tests/qemu-iotests/298
> @@ -0,0 +1,47 @@
> +#!/usr/bin/env python3
> +#
> +# Copyright (C) 2020 Red Hat, Inc.
> +#
> +# This program is free software; you can redistribute it and/or modify
> +# it under the terms of the GNU General Public License as published by
> +# the Free Software Foundation; either version 2 of the License, or
> +# (at your option) any later version.
> +#
> +# This program is distributed in the hope that it will be useful,
> +# but WITHOUT ANY WARRANTY; without even the implied warranty of
> +# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> +# GNU General Public License for more details.
> +#
> +# You should have received a copy of the GNU General Public License
> +# along with this program.  If not, see <http://www.gnu.org/licenses/>.
> +
> +
> +
> +# Regression test for avoiding an assertion when the 'backing file'
> +# parameter (-b) is set to an empty string for qemu-img create
> +#
> +#   qemu-img create -f qcow2 -b '' /tmp/foo
> +#
> +# This ensures the invalid parameter is handled with a user-
> +# friendly message instead of a failed assertion.
> +
> +import iotests
> +
> +class TestEmptyBackingFilename(iotests.QMPTestCase):
> +
> +
> +    def test_empty_backing_file_name(self):
> +        actual = iotests.qemu_img_pipe(
> +                'create',
> +                '-f', 'qcow2',
> +                '-b', '',
> +                '/tmp/foo'
> +        )
> +        expected = 'qemu-img: /tmp/foo: Expected backing file name,' \
> +                   ' got empty string'
> +
> +        self.assertEqual(actual.strip(), expected.strip())
> +
> +
> +if __name__ == '__main__':
> +    iotests.main(supported_fmts=['raw', 'qcow2'])
> diff --git a/tests/qemu-iotests/298.out b/tests/qemu-iotests/298.out
> new file mode 100644
> index 0000000000..ae1213e6f8
> --- /dev/null
> +++ b/tests/qemu-iotests/298.out
> @@ -0,0 +1,5 @@
> +.
> +----------------------------------------------------------------------
> +Ran 1 tests
> +
> +OK
> diff --git a/tests/qemu-iotests/group b/tests/qemu-iotests/group
> index d886fa0cb3..4bca2d9e05 100644
> --- a/tests/qemu-iotests/group
> +++ b/tests/qemu-iotests/group
> @@ -302,3 +302,4 @@
>   291 rw quick
>   292 rw auto quick
>   297 meta
> +298 img auto quick
>