btrfs: add write protection to SET_FEATURES ioctl

Perform the want_write check if we get far enough to do any writes.

Signed-off-by: David Sterba <dsterba@suse.com>

1 files changed, 13 insertions, 3 deletions

diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index 798f58e7338e..1e8ce5247a81 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -5406,9 +5406,15 @@ static int btrfs_ioctl_set_features(struct file *file, void __user *arg)
         if (ret)
                 return ret;
 
+        ret = mnt_want_write_file(file);
+        if (ret)
+                return ret;
+
         trans = btrfs_start_transaction(root, 0);
-        if (IS_ERR(trans))
-                return PTR_ERR(trans);
+        if (IS_ERR(trans)) {
+                ret = PTR_ERR(trans);
+                goto out_drop_write;
+        }
 
         spin_lock(&root->fs_info->super_lock);
         newflags = btrfs_super_compat_flags(super_block);
@@ -5427,7 +5433,11 @@ static int btrfs_ioctl_set_features(struct file *file, void __user *arg)
         btrfs_set_super_incompat_flags(super_block, newflags);
         spin_unlock(&root->fs_info->super_lock);
 
-        return btrfs_commit_transaction(trans, root);
+        ret = btrfs_commit_transaction(trans, root);
+out_drop_write:
+        mnt_drop_write_file(file);
+
+        return ret;
 }
 
 long btrfs_ioctl(struct file *file, unsigned int