Re: [PATCH v3 03/11] documentation: Block Devices Snapshots Module
From: Donald Buczek
Date: Wed Apr 19 2023 - 15:42:15 EST
Dear Sergei,
On 4/19/23 15:05, Sergei Shtepa wrote:
On 4/18/23 16:48, Donald Buczek wrote:
Subject:
Re: [PATCH v3 03/11] documentation: Block Devices Snapshots Module
From:
Donald Buczek <buczek@xxxxxxxxxxxxx>
Date:
4/18/23, 16:48
To:
Sergei Shtepa <sergei.shtepa@xxxxxxxxx>, axboe@xxxxxxxxx, hch@xxxxxxxxxxxxx, corbet@xxxxxxx, snitzer@xxxxxxxxxx
CC:
viro@xxxxxxxxxxxxxxxxxx, brauner@xxxxxxxxxx, willy@xxxxxxxxxxxxx, kch@xxxxxxxxxx, martin.petersen@xxxxxxxxxx, vkoul@xxxxxxxxxx, ming.lei@xxxxxxxxxx, gregkh@xxxxxxxxxxxxxxxxxxx, linux-block@xxxxxxxxxxxxxxx, linux-doc@xxxxxxxxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx, linux-fsdevel@xxxxxxxxxxxxxxx
On 4/18/23 12:31, Sergei Shtepa wrote:
On 4/14/23 14:34, Sergei Shtepa wrote:
Subject:
Re: [PATCH v3 03/11] documentation: Block Devices Snapshots Module
From:
Sergei Shtepa <sergei.shtepa@xxxxxxxxx>
Date:
4/14/23, 14:34
To:
Donald Buczek <buczek@xxxxxxxxxxxxx>, axboe@xxxxxxxxx, hch@xxxxxxxxxxxxx, corbet@xxxxxxx, snitzer@xxxxxxxxxx
CC:
viro@xxxxxxxxxxxxxxxxxx, brauner@xxxxxxxxxx, willy@xxxxxxxxxxxxx, kch@xxxxxxxxxx, martin.petersen@xxxxxxxxxx, vkoul@xxxxxxxxxx, ming.lei@xxxxxxxxxx, gregkh@xxxxxxxxxxxxxxxxxxx, linux-block@xxxxxxxxxxxxxxx, linux-doc@xxxxxxxxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx, linux-fsdevel@xxxxxxxxxxxxxxx
On 4/12/23 21:38, Donald Buczek wrote:
Subject:
Re: [PATCH v3 03/11] documentation: Block Devices Snapshots Module
From:
Donald Buczek <buczek@xxxxxxxxxxxxx>
Date:
4/12/23, 21:38
To:
Sergei Shtepa <sergei.shtepa@xxxxxxxxx>, axboe@xxxxxxxxx, hch@xxxxxxxxxxxxx, corbet@xxxxxxx, snitzer@xxxxxxxxxx
CC:
viro@xxxxxxxxxxxxxxxxxx, brauner@xxxxxxxxxx, willy@xxxxxxxxxxxxx, kch@xxxxxxxxxx, martin.petersen@xxxxxxxxxx, vkoul@xxxxxxxxxx, ming.lei@xxxxxxxxxx, gregkh@xxxxxxxxxxxxxxxxxxx, linux-block@xxxxxxxxxxxxxxx, linux-doc@xxxxxxxxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx, linux-fsdevel@xxxxxxxxxxxxxxx
I think, you can trigger all kind of user-after-free when userspace deletes a snapshot image or the snapshot image and the tracker while the disk device snapshot image is kept alive (mounted or just opened) and doing I/O.
Here is what I did to provoke that:
root@dose:~# s=$(blksnap snapshot_create -d /dev/vdb)
root@dose:~# blksnap snapshot_appendstorage -i $s -f /scratch/local/test.dat
device path: '/dev/block/253:2'
allocate range: ofs=11264624 cnt=2097152
root@dose:~# blksnap snapshot_take -i $s
root@dose:~# mount /dev/blksnap-image_253\:16 /mnt
root@dose:~# dd if=/dev/zero of=/mnt/x.x &
[1] 2514
root@dose:~# blksnap snapshot_destroy -i $s
dd: writing to '/mnt/x.x': No space left on device
1996041+0 records in
1996040+0 records out
1021972480 bytes (1.0 GB, 975 MiB) copied, 8.48923 s, 120 MB/s
[1]+ Exit 1 dd if=/dev/zero of=/mnt/x.x
Thanks!
I am very glad that the blksnap tool turned out to be useful in the review.
This snapshot deletion scenario is not the most typical, but of course it is
quite possible.
I will need to solve this problem and add such a scenario to the test suite.
Hi!
I have redesign the logic of ownership of the diff_area structure.
See patch in attach or commit.
Link: https://github.com/SergeiShtepa/linux/commit/7e927c381dcd2b2293be8315897a224d111b6f88
A test script for such a scenario has been added.
Link: https://github.com/veeam/blksnap/commit/fd0559dfedf094901d08bbf185fed288f0156433
I will be glad of any feedback.
Great, Thanks!
However, there are two leftover calls to diff_area_free() with its old prototype:
CC [M] drivers/block/blksnap/diff_area.o
drivers/block/blksnap/diff_area.c: In function ‘diff_area_new’:
drivers/block/blksnap/diff_area.c:283:18: error: passing argument 1 of ‘diff_area_free’ from incompatible pointer type [-Werror=incompatible-pointer-types]
283 | diff_area_free(diff_area);
| ^~~~~~~~~
| |
| struct diff_area *
drivers/block/blksnap/diff_area.c:110:34: note: expected ‘struct kref *’ but argument is of type ‘struct diff_area *’
110 | void diff_area_free(struct kref *kref)
| ~~~~~~~~~~~~~^~~~
cc1: some warnings being treated as errors
make[4]: *** [scripts/Makefile.build:252: drivers/block/blksnap/diff_area.o] Error 1
make[3]: *** [scripts/Makefile.build:494: drivers/block/blksnap] Error 2
make[2]: *** [scripts/Makefile.build:494: drivers/block] Error 2
make[1]: *** [scripts/Makefile.build:494: drivers] Error 2
make: *** [Makefile:2025: .] Error 2
The other one:
buczek@dose:/scratch/local/linux (blksnap-test)$ make drivers/block/blksnap/tracker.o
CALL scripts/checksyscalls.sh
DESCEND objtool
INSTALL libsubcmd_headers
CC [M] drivers/block/blksnap/tracker.o
drivers/block/blksnap/tracker.c: In function ‘tracker_free’:
drivers/block/blksnap/tracker.c:26:25: error: passing argument 1 of ‘diff_area_free’ from incompatible pointer type [-Werror=incompatible-pointer-types]
26 | diff_area_free(tracker->diff_area);
| ~~~~~~~^~~~~~~~~~~
| |
| struct diff_area *
In file included from drivers/block/blksnap/tracker.c:12:
drivers/block/blksnap/diff_area.h:116:34: note: expected ‘struct kref *’ but argument is of type ‘struct diff_area *’
116 | void diff_area_free(struct kref *kref);
| ~~~~~~~~~~~~~^~~~
cc1: some warnings being treated as errors
make[4]: *** [scripts/Makefile.build:252: drivers/block/blksnap/tracker.o] Error 1
make[3]: *** [scripts/Makefile.build:494: drivers/block/blksnap] Error 2
make[2]: *** [scripts/Makefile.build:494: drivers/block] Error 2
make[1]: *** [scripts/Makefile.build:494: drivers] Error 2
make: *** [Makefile:2025: .] Error 2
Am I missing something?
Thanks!
It seems to me that I missed something.
The biggest mystery for me is why I was able to build and test the kernel.
I think it's some kind of incremental build effect.
I was only able to see the problem after 'make clean'.
Patches in attach and https://github.com/SergeiShtepa/linux/tree/blksnap-master
Thanks. I can confirm that this fixes the reported problem and I no longer can trigger the UAF. :-)
Tested-Bny: Donald Buczek <buczek@xxxxxxxxxxxxx>
Maybe you can add me to the cc list for v4 as I'm not subscribed to the lists.
Best
Donald
--
Donald Buczek
buczek@xxxxxxxxxxxxx
Tel: +49 30 8413 1433