btrfs: read entire device info under lock

There's a theoretical possibility of reading stale (or even more
theoretically, freed) data from DEV_INFO ioctl when the device would
disappear between an early mutex unlock and data being copied from the
device structure.

Signed-off-by: David Sterba <dsterba@suse.cz>
Signed-off-by: Josef Bacik <jbacik@fusionio.com>

diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index 3aa3750..0de4a2f 100644 (file)
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -2432,7 +2432,6 @@ static long btrfs_ioctl_dev_info(struct btrfs_root *root, void __user *arg)
 
        mutex_lock(&fs_devices->device_list_mutex);
        dev = btrfs_find_device(root->fs_info, di_args->devid, s_uuid, NULL);
-       mutex_unlock(&fs_devices->device_list_mutex);
 
        if (!dev) {
                ret = -ENODEV;
@@ -2456,6 +2455,7 @@ static long btrfs_ioctl_dev_info(struct btrfs_root *root, void __user *arg)
        }
 
 out:
+       mutex_unlock(&fs_devices->device_list_mutex);
        if (ret == 0 && copy_to_user(arg, di_args, sizeof(*di_args)))
                ret = -EFAULT;