Re: [PATCH v3 03/11] documentation: Block Devices Snapshots Module
From: Sergei Shtepa
Date: Wed Apr 19 2023 - 09:05:50 EST
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-masterdiff --git a/drivers/block/blksnap/diff_area.h b/drivers/block/blksnap/diff_area.h
index cb3e09809c0f..883117dba762 100644
--- a/drivers/block/blksnap/diff_area.h
+++ b/drivers/block/blksnap/diff_area.h
@@ -138,6 +138,5 @@ bool diff_area_cow(struct bio *bio, struct diff_area *diff_area,
bool diff_area_submit_chunk(struct diff_area *diff_area, struct bio *bio);
void diff_area_rw_chunk(struct kref *kref);
-//void diff_area_throttling_io(struct diff_area *diff_area);
#endif /* __BLKSNAP_DIFF_AREA_H */
diff --git a/drivers/block/blksnap/diff_area.c b/drivers/block/blksnap/diff_area.c
index 5a3f4d74a92f..0e530d24d563 100644
--- a/drivers/block/blksnap/diff_area.c
+++ b/drivers/block/blksnap/diff_area.c
@@ -280,7 +280,7 @@ struct diff_area *diff_area_new(dev_t dev_id, struct diff_storage *diff_storage)
}
if (ret) {
- diff_area_free(diff_area);
+ diff_area_put(diff_area);
return ERR_PTR(ret);
}
diff --git a/drivers/block/blksnap/tracker.c b/drivers/block/blksnap/tracker.c
index 6d2c77e4c90f..d98048dc5bed 100644
--- a/drivers/block/blksnap/tracker.c
+++ b/drivers/block/blksnap/tracker.c
@@ -23,7 +23,7 @@ void tracker_free(struct kref *kref)
MINOR(tracker->dev_id));
if (tracker->diff_area)
- diff_area_free(tracker->diff_area);
+ diff_area_put(tracker->diff_area);
if (tracker->cbt_map)
cbt_map_destroy(tracker->cbt_map);