btrfs: Require CAP_SYS_ADMIN for filesystem rebalance

commit 6f88a4403def422bd8e276ddf6863d6ac71435d2 upstream.

Filesystem rebalancing (BTRFS_IOC_BALANCE) affects the entire
filesystem and may run uninterruptibly for a long time.  This does not
seem to be something that an unprivileged user should be able to do.

Reported-by: Aron Xu <happyaron.xu@gmail.com>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Signed-off-by: Chris Mason <chris.mason@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index 41ecbb2347f2d3171f7645782ab4e5a39621c84d..5d56a8dab69b2eda4a2e6d1fb518a719bd2acb51 100644 (file)
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -21,6 +21,7 @@
 #include <linux/blkdev.h>
 #include <linux/random.h>
 #include <linux/iocontext.h>
+#include <linux/capability.h>
 #include <asm/div64.h>
 #include "compat.h"
 #include "ctree.h"
@@ -1900,6 +1901,9 @@ int btrfs_balance(struct btrfs_root *dev_root)
        if (dev_root->fs_info->sb->s_flags & MS_RDONLY)
                return -EROFS;
 
+       if (!capable(CAP_SYS_ADMIN))
+               return -EPERM;
+
        mutex_lock(&dev_root->fs_info->volume_mutex);
        dev_root = dev_root->fs_info->dev_root;