Re: [PATCH v3 03/11] documentation: Block Devices Snapshots Module
From: Sergei Shtepa
Date: Fri Apr 21 2023 - 13:32:51 EST
On 4/20/23 21:17, Sergei Shtepa wrote:
> Subject:
> Re: [PATCH v3 03/11] documentation: Block Devices Snapshots Module
> From:
> Sergei Shtepa <sergei.shtepa@xxxxxxxxx>
> Date:
> 4/20/23, 21:17
>
> 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 4/20/23 16:44, Donald Buczek wrote:
>> Subject:
>> Re: [PATCH v3 03/11] documentation: Block Devices Snapshots Module
>> From:
>> Donald Buczek <buczek@xxxxxxxxxxxxx>
>> Date:
>> 4/20/23, 16:44
>>
>> 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 4/19/23 21:42, Donald Buczek wrote:
>>> Dear Sergei,
>>>
>>> On 4/19/23 15:05, Sergei Shtepa wrote:
>>>> [...]
>>>>
>>>> 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.
>>
>> Sorry, found another one. Reproducer:
>>
>> =====
>> #! /bin/bash
>> set -xe
>> modprobe blksnap
>> test -e /scratch/local/test.dat || fallocate -l 1G /scratch/local/test.dat
>> s=$(blksnap snapshot_create -d /dev/vdb)
>> blksnap snapshot_appendstorage -i $s -f /scratch/local/test.dat
>> blksnap snapshot_take -i $s
>> s2=$(blksnap snapshot_create -d /dev/vdb)
>> blksnap snapshot_destroy -i $s2
>> blksnap snapshot_destroy -i $s
>> =====
>>
>>
>> [20382.402921] blksnap-snapshot: Snapshot ff1c54f1-3e8c-4c99-bb26-35e82dc1c9fa was created
>> [20382.535933] blksnap-image: Create snapshot image device for original device [253:16]
>> [20382.542405] blksnap-snapshot: Snapshot ff1c54f1-3e8c-4c99-bb26-35e82dc1c9fa was taken successfully
>> [20382.572564] blksnap-snapshot: Snapshot 4b2d571d-9a24-419d-96c2-8d64a07c4966 was created
>> [20382.600521] blksnap-snapshot: Destroy snapshot 4b2d571d-9a24-419d-96c2-8d64a07c4966
>> [20382.602373] blksnap-snapshot: Release snapshot 4b2d571d-9a24-419d-96c2-8d64a07c4966
>> [20382.722137] blksnap-snapshot: Destroy snapshot ff1c54f1-3e8c-4c99-bb26-35e82dc1c9fa
>> [20382.724033] blksnap-snapshot: Release snapshot ff1c54f1-3e8c-4c99-bb26-35e82dc1c9fa
>> [20382.725850] ==================================================================
>> [20382.727641] BUG: KASAN: wild-memory-access in snapshot_free+0x73/0x170 [blksnap]
>> [20382.729326] Write of size 8 at addr dead000000000108 by task blksnap/8297
>> ...
> Great! Thanks.
>
> There is no protection against re-adding a block device to the snapshot.
> I'll take care of it.
>
Hi!
I think the fix turned out to be quite beautiful.
Now you will get an error "Device or resource busy".
Fix in attach and on github.
Link: https://github.com/SergeiShtepa/linux/commit/43a5d3dd9858f092b734187b6a62ce75acaa47c7
diff --git a/drivers/block/blksnap/snapshot.c b/drivers/block/blksnap/snapshot.c
index 1f28ff59d762..8063cc4b929e 100644
--- a/drivers/block/blksnap/snapshot.c
+++ b/drivers/block/blksnap/snapshot.c
@@ -28,7 +28,7 @@ static void snapshot_free(struct kref *kref)
tracker = list_first_entry(&snapshot->trackers, struct tracker,
link);
- list_del(&tracker->link);
+ list_del_init(&tracker->link);
tracker_release_snapshot(tracker);
tracker_put(tracker);
}
@@ -160,14 +160,17 @@ int snapshot_add_device(const uuid_t *id, struct tracker *tracker)
}
}
if (!ret) {
- tracker_get(tracker);
- list_add_tail(&tracker->link, &snapshot->trackers);
+ if (list_empty(&tracker->link)) {
+ tracker_get(tracker);
+ list_add_tail(&tracker->link, &snapshot->trackers);
+ } else
+ ret = -EBUSY;
}
up_write(&snapshot->rw_lock);
snapshot_put(snapshot);
- return 0;
+ return ret;
}
int snapshot_destroy(const uuid_t *id)
diff --git a/drivers/block/blksnap/tracker.c b/drivers/block/blksnap/tracker.c
index d98048dc5bed..008cc7f0f81e 100644
--- a/drivers/block/blksnap/tracker.c
+++ b/drivers/block/blksnap/tracker.c
@@ -79,6 +79,7 @@ static struct blkfilter *tracker_attach(struct block_device *bdev)
return ERR_PTR(-ENOMEM);
}
+ mutex_init(&tracker->ctl_lock);
INIT_LIST_HEAD(&tracker->link);
kref_init(&tracker->kref);
tracker->dev_id = bdev->bd_dev;
@@ -234,12 +235,17 @@ static int (*const ctl_table[])(struct tracker *tracker,
static int tracker_ctl(struct blkfilter *flt, const unsigned int cmd,
__u8 __user *buf, __u32 *plen)
{
+ int ret = 0;
struct tracker *tracker = container_of(flt, struct tracker, filter);
if (cmd > ARRAY_SIZE(ctl_table))
return -ENOTTY;
- return ctl_table[cmd](tracker, buf, plen);
+ mutex_lock(&tracker->ctl_lock);
+ ret = ctl_table[cmd](tracker, buf, plen);
+ mutex_unlock(&tracker->ctl_lock);
+
+ return ret;
}
static struct blkfilter_operations tracker_ops = {
diff --git a/drivers/block/blksnap/tracker.h b/drivers/block/blksnap/tracker.h
index d0972994d528..dbf8295f9518 100644
--- a/drivers/block/blksnap/tracker.h
+++ b/drivers/block/blksnap/tracker.h
@@ -19,6 +19,9 @@ struct diff_area;
*
* @filter:
* The block device filter structure.
+ * @ctl_lock:
+ * The mutex blocks simultaneous management of the tracker from different
+ * treads.
* @link:
* List header. Allows to combine trackers into a list in a snapshot.
* @kref:
@@ -41,6 +44,7 @@ struct diff_area;
*/
struct tracker {
struct blkfilter filter;
+ struct mutex ctl_lock;
struct list_head link;
struct kref kref;
dev_t dev_id;