4.18-stable review patch. If anyone has any objections, please let me know.
------------------
From: David Sterba <dsterba@xxxxxxxx>
[ Upstream commit 81ffd56b5745355b70d54ca4e1bdd0d64a66ff9f ]
Technically this extends the critical section covered by uuid_mutex to:
- parse early mount options -- here we can call device scan on paths
that can be passed as 'device=/dev/...'
- scan the device passed to mount
- open the devices related to the fs_devices -- this increases
fs_devices::opened
The race can happen when mount calls one of the scans and there's
another one called eg. by mkfs or 'btrfs dev scan':
Mount Scan
----- ----
scan_one_device (dev1, fsid1)
scan_one_device (dev2, fsid1)
add the device
free stale devices
fsid1 fs_devices::opened == 0
find fsid1:dev1
free fsid1:dev1
if it's the last one,
free fs_devices of fsid1
too
open_devices (dev1, fsid1)
dev1 not found
When fixed, the uuid mutex will make sure that mount will increase
fs_devices::opened and this will not be touched by the racing scan
ioctl.
Reported-and-tested-by: syzbot+909a5177749d7990ffa4@xxxxxxxxxxxxxxxxxxxxxxxxx
Reported-and-tested-by: syzbot+ceb2606025ec1cc3479c@xxxxxxxxxxxxxxxxxxxxxxxxx
Reviewed-by: Anand Jain <anand.jain@xxxxxxxxxx>
Signed-off-by: David Sterba <dsterba@xxxxxxxx>
Signed-off-by: Sasha Levin <alexander.levin@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
fs/btrfs/super.c | 12 ++++++------
1 file changed, 6 insertions(+), 6 deletions(-)
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -1557,19 +1557,19 @@ static struct dentry *btrfs_mount_root(s
mutex_lock(&uuid_mutex);
error = btrfs_parse_early_options(data, mode, fs_type, &fs_devices);
- mutex_unlock(&uuid_mutex);
- if (error)
+ if (error) {
+ mutex_unlock(&uuid_mutex);
goto error_fs_info;
+ }
- mutex_lock(&uuid_mutex);
error = btrfs_scan_one_device(device_name, mode, fs_type, &fs_devices);
- mutex_unlock(&uuid_mutex);
- if (error)
+ if (error) {
+ mutex_unlock(&uuid_mutex);
goto error_fs_info;
+ }
fs_info->fs_devices = fs_devices;
- mutex_lock(&uuid_mutex);
error = btrfs_open_devices(fs_devices, mode, fs_type);
mutex_unlock(&uuid_mutex);
if (error)
