linux-kernel - [PATCH 4.5 119/128] btrfs: add write protection to SET

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Date:	Sun,  5 Jun 2016 15:24:34 -0700
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	linux-kernel@...r.kernel.org
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	stable@...r.kernel.org, David Sterba <dsterba@...e.com>
Subject: [PATCH 4.5 119/128] btrfs: add write protection to SET_FEATURES ioctl

4.5-stable review patch.  If anyone has any objections, please let me know.

------------------

From: David Sterba <dsterba@...e.cz>

commit 7ab19625a911f7568ec85302e3aa7a64186006c8 upstream.

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

Signed-off-by: David Sterba <dsterba@...e.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 fs/btrfs/ioctl.c |   16 +++++++++++++---
 1 file changed, 13 insertions(+), 3 deletions(-)

--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -5397,9 +5397,15 @@ static int btrfs_ioctl_set_features(stru
 	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);
@@ -5418,7 +5424,11 @@ static int btrfs_ioctl_set_features(stru
 	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