linux-kernel - [PATCH 3.16.y-ckt 145/183] debugfs: leave freeing a symlink body until inode eviction

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Message-Id: <1425635874-19087-146-git-send-email-luis.henriques@canonical.com>
Date:	Fri,  6 Mar 2015 09:57:16 +0000
From:	Luis Henriques <luis.henriques@...onical.com>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	kernel-team@...ts.ubuntu.com
Cc:	Al Viro <viro@...iv.linux.org.uk>,
	Luis Henriques <luis.henriques@...onical.com>
Subject: [PATCH 3.16.y-ckt 145/183] debugfs: leave freeing a symlink body until inode eviction

3.16.7-ckt8 -stable review patch.  If anyone has any objections, please let me know.

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

From: Al Viro <viro@...iv.linux.org.uk>

commit 0db59e59299f0b67450c5db21f7f316c8fb04e84 upstream.

As it is, we have debugfs_remove() racing with symlink traversals.
Supply ->evict_inode() and do freeing there - inode will remain
pinned until we are done with the symlink body.

And rip the idiocy with checking if dentry is positive right after
we'd verified debugfs_positive(), which is a stronger check...

Signed-off-by: Al Viro <viro@...iv.linux.org.uk>
Signed-off-by: Luis Henriques <luis.henriques@...onical.com>
---
 fs/debugfs/inode.c | 34 +++++++++++++++++-----------------
 1 file changed, 17 insertions(+), 17 deletions(-)

diff --git a/fs/debugfs/inode.c b/fs/debugfs/inode.c
index dc240009e8ec..0c6ba4ef00a0 100644
--- a/fs/debugfs/inode.c
+++ b/fs/debugfs/inode.c
@@ -246,10 +246,19 @@ static int debugfs_show_options(struct seq_file *m, struct dentry *root)
 	return 0;
 }
 
+static void debugfs_evict_inode(struct inode *inode)
+{
+	truncate_inode_pages_final(&inode->i_data);
+	clear_inode(inode);
+	if (S_ISLNK(inode->i_mode))
+		kfree(inode->i_private);
+}
+
 static const struct super_operations debugfs_super_operations = {
 	.statfs		= simple_statfs,
 	.remount_fs	= debugfs_remount,
 	.show_options	= debugfs_show_options,
+	.evict_inode	= debugfs_evict_inode,
 };
 
 static int debug_fill_super(struct super_block *sb, void *data, int silent)
@@ -466,23 +475,14 @@ static int __debugfs_remove(struct dentry *dentry, struct dentry *parent)
 	int ret = 0;
 
 	if (debugfs_positive(dentry)) {
-		if (dentry->d_inode) {
-			dget(dentry);
-			switch (dentry->d_inode->i_mode & S_IFMT) {
-			case S_IFDIR:
-				ret = simple_rmdir(parent->d_inode, dentry);
-				break;
-			case S_IFLNK:
-				kfree(dentry->d_inode->i_private);
-				/* fall through */
-			default:
-				simple_unlink(parent->d_inode, dentry);
-				break;
-			}
-			if (!ret)
-				d_delete(dentry);
-			dput(dentry);
-		}
+		dget(dentry);
+		if (S_ISDIR(dentry->d_inode->i_mode))
+			ret = simple_rmdir(parent->d_inode, dentry);
+		else
+			simple_unlink(parent->d_inode, dentry);
+		if (!ret)
+			d_delete(dentry);
+		dput(dentry);
 	}
 	return ret;
 }
--
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