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>

diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index 798f58e..1e8ce52 100644 (file)
--- 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