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 <[email protected]>
Signed-off-by: Ben Hutchings <[email protected]>
---
 fs/btrfs/volumes.c |    4 ++++
 1 files changed, 4 insertions(+), 0 deletions(-)

diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index cc04dc1..2313e8b 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -22,6 +22,7 @@
 #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"
@@ -1905,6 +1906,9 @@ 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;
 
-- 
1.7.2.3


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