Re: [Qemu-devel] [PATCH 2/5] qcow1: Check maximum cluster size

[Kevin Wolf]

Am 12.05.2014 um 17:00 hat Benoît Canet geschrieben:
> The Monday 12 May 2014 à 15:04:08 (+0200), Kevin Wolf wrote :
> > Huge values for header.cluster_bits cause unbounded allocations (e.g.
> > for s->cluster_cache) and crash qemu this way. Less huge values may
> > survive those allocations, but can cause integer overflows later on.
> > 
> > The only cluster sizes that qemu can create are 4k (for standalone
> > images) and 512 (for images with backing files), so we can limit it
> > to 64k.
> > 
> > Signed-off-by: Kevin Wolf <address@hidden>
> > ---
> >  block/qcow.c               | 10 ++++++--
> >  tests/qemu-iotests/092     | 60 
> > ++++++++++++++++++++++++++++++++++++++++++++++
> >  tests/qemu-iotests/092.out |  9 +++++++
> >  tests/qemu-iotests/group   |  1 +
> >  4 files changed, 78 insertions(+), 2 deletions(-)
> >  create mode 100755 tests/qemu-iotests/092
> >  create mode 100644 tests/qemu-iotests/092.out
> > 
> > diff --git a/block/qcow.c b/block/qcow.c
> > index 3684794..e60df23 100644
> > --- a/block/qcow.c
> > +++ b/block/qcow.c
> > @@ -128,11 +128,17 @@ static int qcow_open(BlockDriverState *bs, QDict 
> > *options, int flags,
> >          goto fail;
> >      }
> >  
> > -    if (header.size <= 1 || header.cluster_bits < 9) {
> > -        error_setg(errp, "invalid value in qcow header");
> > +    if (header.size <= 1) {
> > +        error_setg(errp, "Image size is too small (must be at least 2 
> > bytes)");
> >          ret = -EINVAL;
> >          goto fail;
> >      }
> > +    if (header.cluster_bits < 9 || header.cluster_bits > 16) {
> > +        error_setg(errp, "Cluster size must be between 512 and 64k");
> > +        ret = -EINVAL;
> > +        goto fail;
> > +    }
> > +
> >      if (header.crypt_method > QCOW_CRYPT_AES) {
> >          error_setg(errp, "invalid encryption method in qcow header");
> >          ret = -EINVAL;
> > diff --git a/tests/qemu-iotests/092 b/tests/qemu-iotests/092
> > new file mode 100755
> > index 0000000..b0f04e3
> > --- /dev/null
> > +++ b/tests/qemu-iotests/092
> > @@ -0,0 +1,60 @@
> > +#!/bin/bash
> > +#
> > +# qcow1 format input validation tests
> > +#
> > +# Copyright (C) 2014 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/>.
> > +#
> > +
> > +# creator
> > address@hidden
> > +
> > +seq=`basename $0`
> > +echo "QA output created by $seq"
> > +
> > +here=`pwd`
> > +tmp=/tmp/$$
> > +status=1   # failure is the default!
> > +
> > +_cleanup()
> > +{
> > +    rm -f $TEST_IMG.snap
> > +    _cleanup_test_img
> > +}
> > +trap "_cleanup; exit \$status" 0 1 2 3 15
> > +
> > +# get standard environment, filters and checks
> > +. ./common.rc
> > +. ./common.filter
> > +
> > +_supported_fmt qcow
> > +_supported_proto generic
> > +_supported_os Linux
> > +
> > +offset_cluster_bits=32
> 
> > +offset_l2_bits=33
> This seems to be an extra.

Moving this line to the next patch.

> > +
> > +echo
> > +echo "== Invalid cluster size =="
> > +_make_test_img 64M
> 
> 
> > +poke_file "$TEST_IMG" "$offset_cluster_bits" "\xff"
> > +{ $QEMU_IO -c "read 0 512" $TEST_IMG; } 2>&1 | _filter_qemu_io | 
> > _filter_testdir
> > +poke_file "$TEST_IMG" "$offset_cluster_bits" "\x1f"
> > +{ $QEMU_IO -c "read 0 512" $TEST_IMG; } 2>&1 | _filter_qemu_io | 
> > _filter_testdir
> 
> From the code " +    if (header.cluster_bits < 9 || header.cluster_bits > 16) 
> {"
> 
> Shouldn't the hex values be "\x08" and "\x11" ?

Those values actually kind of work, it needs something bigger to crash
qemu. But I'll add those two values as well.

Kevin