From: Max Reitz <mreitz@redhat.com>
To: qemu-block@nongnu.org
Cc: Kevin Wolf <kwolf@redhat.com>,
Peter Maydell <peter.maydell@linaro.org>,
qemu-devel@nongnu.org, Max Reitz <mreitz@redhat.com>
Subject: [PULL 3/6] block: bdrv_set_backing_bs: fix use-after-free
Date: Tue, 24 Mar 2020 13:20:41 +0100 [thread overview]
Message-ID: <20200324122044.1131326-4-mreitz@redhat.com> (raw)
In-Reply-To: <20200324122044.1131326-1-mreitz@redhat.com>
From: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
There is a use-after-free possible: bdrv_unref_child() leaves
bs->backing freed but not NULL. bdrv_attach_child may produce nested
polling loop due to drain, than access of freed pointer is possible.
I've produced the following crash on 30 iotest with modified code. It
does not reproduce on master, but still seems possible:
#0 __strcmp_avx2 () at /lib64/libc.so.6
#1 bdrv_backing_overridden (bs=0x55c9d3cc2060) at block.c:6350
#2 bdrv_refresh_filename (bs=0x55c9d3cc2060) at block.c:6404
#3 bdrv_backing_attach (c=0x55c9d48e5520) at block.c:1063
#4 bdrv_replace_child_noperm
(child=child@entry=0x55c9d48e5520,
new_bs=new_bs@entry=0x55c9d3cc2060) at block.c:2290
#5 bdrv_replace_child
(child=child@entry=0x55c9d48e5520,
new_bs=new_bs@entry=0x55c9d3cc2060) at block.c:2320
#6 bdrv_root_attach_child
(child_bs=child_bs@entry=0x55c9d3cc2060,
child_name=child_name@entry=0x55c9d241d478 "backing",
child_role=child_role@entry=0x55c9d26ecee0 <child_backing>,
ctx=<optimized out>, perm=<optimized out>, shared_perm=21,
opaque=0x55c9d3c5a3d0, errp=0x7ffd117108e0) at block.c:2424
#7 bdrv_attach_child
(parent_bs=parent_bs@entry=0x55c9d3c5a3d0,
child_bs=child_bs@entry=0x55c9d3cc2060,
child_name=child_name@entry=0x55c9d241d478 "backing",
child_role=child_role@entry=0x55c9d26ecee0 <child_backing>,
errp=errp@entry=0x7ffd117108e0) at block.c:5876
#8 in bdrv_set_backing_hd
(bs=bs@entry=0x55c9d3c5a3d0,
backing_hd=backing_hd@entry=0x55c9d3cc2060,
errp=errp@entry=0x7ffd117108e0)
at block.c:2576
#9 stream_prepare (job=0x55c9d49d84a0) at block/stream.c:150
#10 job_prepare (job=0x55c9d49d84a0) at job.c:761
#11 job_txn_apply (txn=<optimized out>, fn=<optimized out>) at
job.c:145
#12 job_do_finalize (job=0x55c9d49d84a0) at job.c:778
#13 job_completed_txn_success (job=0x55c9d49d84a0) at job.c:832
#14 job_completed (job=0x55c9d49d84a0) at job.c:845
#15 job_completed (job=0x55c9d49d84a0) at job.c:836
#16 job_exit (opaque=0x55c9d49d84a0) at job.c:864
#17 aio_bh_call (bh=0x55c9d471a160) at util/async.c:117
#18 aio_bh_poll (ctx=ctx@entry=0x55c9d3c46720) at util/async.c:117
#19 aio_poll (ctx=ctx@entry=0x55c9d3c46720,
blocking=blocking@entry=true)
at util/aio-posix.c:728
#20 bdrv_parent_drained_begin_single (poll=true, c=0x55c9d3d558f0)
at block/io.c:121
#21 bdrv_parent_drained_begin_single (c=c@entry=0x55c9d3d558f0,
poll=poll@entry=true)
at block/io.c:114
#22 bdrv_replace_child_noperm
(child=child@entry=0x55c9d3d558f0,
new_bs=new_bs@entry=0x55c9d3d27300) at block.c:2258
#23 bdrv_replace_child
(child=child@entry=0x55c9d3d558f0,
new_bs=new_bs@entry=0x55c9d3d27300) at block.c:2320
#24 bdrv_root_attach_child
(child_bs=child_bs@entry=0x55c9d3d27300,
child_name=child_name@entry=0x55c9d241d478 "backing",
child_role=child_role@entry=0x55c9d26ecee0 <child_backing>,
ctx=<optimized out>, perm=<optimized out>, shared_perm=21,
opaque=0x55c9d3cc2060, errp=0x7ffd11710c60) at block.c:2424
#25 bdrv_attach_child
(parent_bs=parent_bs@entry=0x55c9d3cc2060,
child_bs=child_bs@entry=0x55c9d3d27300,
child_name=child_name@entry=0x55c9d241d478 "backing",
child_role=child_role@entry=0x55c9d26ecee0 <child_backing>,
errp=errp@entry=0x7ffd11710c60) at block.c:5876
#26 bdrv_set_backing_hd
(bs=bs@entry=0x55c9d3cc2060,
backing_hd=backing_hd@entry=0x55c9d3d27300,
errp=errp@entry=0x7ffd11710c60)
at block.c:2576
#27 stream_prepare (job=0x55c9d495ead0) at block/stream.c:150
...
Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Message-Id: <20200316060631.30052-2-vsementsov@virtuozzo.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: John Snow <jsnow@redhat.com>
Signed-off-by: Max Reitz <mreitz@redhat.com>
---
block.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/block.c b/block.c
index 6b984dc883..cccae5add9 100644
--- a/block.c
+++ b/block.c
@@ -2760,10 +2760,10 @@ void bdrv_set_backing_hd(BlockDriverState *bs, BlockDriverState *backing_hd,
if (bs->backing) {
bdrv_unref_child(bs, bs->backing);
+ bs->backing = NULL;
}
if (!backing_hd) {
- bs->backing = NULL;
goto out;
}
--
2.25.1
next prev parent reply other threads:[~2020-03-24 12:23 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-03-24 12:20 [PULL 0/6] Block patches for 5.0-rc0 Max Reitz
2020-03-24 12:20 ` [PULL 1/6] block: Avoid memleak on qcow2 image info failure Max Reitz
2020-03-24 12:20 ` [PULL 2/6] block: Assert BlockDriver::format_name is not NULL Max Reitz
2020-03-24 12:20 ` Max Reitz [this message]
2020-03-24 12:20 ` [PULL 4/6] block/qcow2: zero data_file child after free Max Reitz
2020-03-24 12:20 ` [PULL 5/6] iotests: Fix cleanup path in some tests Max Reitz
2020-03-24 12:20 ` [PULL 6/6] iotests/026: Move v3-exclusive test to new file Max Reitz
2020-03-24 14:52 ` [PULL 0/6] Block patches for 5.0-rc0 Peter Maydell
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20200324122044.1131326-4-mreitz@redhat.com \
--to=mreitz@redhat.com \
--cc=kwolf@redhat.com \
--cc=peter.maydell@linaro.org \
--cc=qemu-block@nongnu.org \
--cc=qemu-devel@nongnu.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.