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qcow2: Avoid integer wraparound in qcow2_co_truncate()

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After commit f01643fb8b when an image is
extended and BDRV_REQ_ZERO_WRITE is set then the new clusters are
zeroized.

The code however does not detect correctly situations when the old and
the new end of the image are within the same cluster. The problem can
be reproduced with these steps:

   qemu-img create -f qcow2 backing.qcow2 1M
   qemu-img create -f qcow2 -F qcow2 -b backing.qcow2 top.qcow2
   qemu-img resize --shrink top.qcow2 520k
   qemu-img resize top.qcow2 567k

In the last step offset - zero_start causes an integer wraparound.

Signed-off-by: Alberto Garcia <berto@igalia.com>
Message-Id: <20200504155217.10325-1-berto@igalia.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
This commit is contained in:
Alberto Garcia 2020-05-04 17:52:17 +02:00 committed by Kevin Wolf
parent 5fc2b4f218
commit e4d7019e1a
4 changed files with 105 additions and 5 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

12
block/qcow2.c
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@ -4242,15 +4242,17 @@ static int coroutine_fn qcow2_co_truncate(BlockDriverState *bs, int64_t offset,
* requires a cluster-aligned start. The end may be unaligned if it is
* at the end of the image (which it is here).
*/
ret = qcow2_cluster_zeroize(bs, zero_start, offset - zero_start, 0);
if (ret < 0) {
error_setg_errno(errp, -ret, "Failed to zero out new clusters");
goto fail;
if (offset > zero_start) {
ret = qcow2_cluster_zeroize(bs, zero_start, offset - zero_start, 0);
if (ret < 0) {
error_setg_errno(errp, -ret, "Failed to zero out new clusters");
goto fail;
}
}
/* Write explicit zeros for the unaligned head */
if (zero_start > old_length) {
uint64_t len = zero_start - old_length;
uint64_t len = MIN(zero_start, offset) - old_length;
uint8_t *buf = qemu_blockalign0(bs, len);
QEMUIOVector qiov;
qemu_iovec_init_buf(&qiov, buf, len);

73
tests/qemu-iotests/292 Executable file
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@ -0,0 +1,73 @@
#!/usr/bin/env bash
#
# Test resizing a qcow2 image with a backing file
#
# Copyright (C) 2020 Igalia, S.L.
# Author: Alberto Garcia <berto@igalia.com>
#
# 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
owner=berto@igalia.com
seq=`basename $0`
echo "QA output created by $seq"
status=1 # failure is the default!
_cleanup()
{
_cleanup_test_img
}
trap "_cleanup; exit \$status" 0 1 2 3 15
# get standard environment, filters and checks
. ./common.rc
. ./common.filter
_supported_fmt qcow2
_supported_proto file
_supported_os Linux
echo '### Create the backing image'
BACKING_IMG="$TEST_IMG.base"
TEST_IMG="$BACKING_IMG" _make_test_img 1M
echo '### Fill the backing image with data (0x11)'
$QEMU_IO -c 'write -P 0x11 0 1M' "$BACKING_IMG" | _filter_qemu_io
echo '### Create the top image'
_make_test_img -F "$IMGFMT" -b "$BACKING_IMG"
echo '### Fill the top image with data (0x22)'
$QEMU_IO -c 'write -P 0x22 0 1M' "$TEST_IMG" | _filter_qemu_io
# Both offsets are part of the same cluster.
echo '### Shrink the image to 520k'
$QEMU_IMG resize --shrink "$TEST_IMG" 520k
echo '### Grow the image to 567k'
$QEMU_IMG resize "$TEST_IMG" 567k
echo '### Check that the tail of the image reads as zeroes'
$QEMU_IO -c 'read -P 0x22 0 520k' "$TEST_IMG" | _filter_qemu_io
$QEMU_IO -c 'read -P 0x00 520k 47k' "$TEST_IMG" | _filter_qemu_io
echo '### Show output of qemu-img map'
$QEMU_IMG map "$TEST_IMG" | _filter_testdir
# success, all done
echo "*** done"
rm -f $seq.full
status=0

24
tests/qemu-iotests/292.out Normal file
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@ -0,0 +1,24 @@
QA output created by 292
### Create the backing image
Formatting 'TEST_DIR/t.IMGFMT.base', fmt=IMGFMT size=1048576
### Fill the backing image with data (0x11)
wrote 1048576/1048576 bytes at offset 0
1 MiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
### Create the top image
Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=1048576 backing_file=TEST_DIR/t.IMGFMT.base backing_fmt=IMGFMT
### Fill the top image with data (0x22)
wrote 1048576/1048576 bytes at offset 0
1 MiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
### Shrink the image to 520k
Image resized.
### Grow the image to 567k
Image resized.
### Check that the tail of the image reads as zeroes
read 532480/532480 bytes at offset 0
520 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
read 48128/48128 bytes at offset 532480
47 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
### Show output of qemu-img map
Offset Length Mapped to File
0 0x8dc00 0x50000 TEST_DIR/t.qcow2
*** done

1
tests/qemu-iotests/group
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@ -298,3 +298,4 @@
288 quick
289 rw quick
290 rw auto quick
292 rw auto quick