From 81ffd56b5745355b70d54ca4e1bdd0d64a66ff9f Mon Sep 17 00:00:00 2001 From: David Sterba Date: Tue, 19 Jun 2018 18:04:07 +0200 Subject: btrfs: fix mount and ioctl device scan ioctl race 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@syzkaller.appspotmail.com Reported-and-tested-by: syzbot+ceb2606025ec1cc3479c@syzkaller.appspotmail.com Reviewed-by: Anand Jain Signed-off-by: David Sterba --- fs/btrfs/super.c | 12 ++++++------ 1 file changed, 6 insertions(+), 6 deletions(-) (limited to 'fs/btrfs/super.c') diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c index d33fc1fc4285..28ab75ebb983 100644 --- a/fs/btrfs/super.c +++ b/fs/btrfs/super.c @@ -1555,19 +1555,19 @@ static struct dentry *btrfs_mount_root(struct file_system_type *fs_type, 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) -- cgit