linux-kernel - [PATCH] configfs: Fix potential NULL d

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Message-ID: <20150127151839.31483.83547.stgit@warthog.procyon.org.uk>
Date:	Tue, 27 Jan 2015 15:18:39 +0000
From:	David Howells <dhowells@...hat.com>
To:	viro@...iv.linux.org.uk
Cc:	dhowells@...hat.com, linux-fsdevel@...r.kernel.org,
	Joel Becker <joel.becker@...cle.com>,
	linux-kernel@...r.kernel.org
Subject: [PATCH] configfs: Fix potential NULL d_inode dereference

Code that does this:

		if (!(d_unhashed(dentry) && dentry->d_inode)) {
			...
			simple_unlink(parent->d_inode, dentry);
		}

is broken because:

    !(d_unhashed(dentry) && dentry->d_inode)

is equivalent to:

    !d_unhashed(dentry) || !dentry->d_inode

so it is possible to get into simple_unlink() with dentry->d_inode == NULL.

simple_unlink(), however, assumes dentry->d_inode cannot be NULL.

I think that what was meant is this:

    !d_unhashed(dentry) && dentry->d_inode

and that the logical-not operator or the final close-bracket was misplaced.

Signed-off-by: David Howells <dhowells@...hat.com>
cc: Joel Becker <joel.becker@...cle.com>
---

 fs/configfs/inode.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/configfs/inode.c b/fs/configfs/inode.c
index 5946ad98053f..e5a7c18a9bee 100644
--- a/fs/configfs/inode.c
+++ b/fs/configfs/inode.c
@@ -249,7 +249,7 @@ void configfs_drop_dentry(struct configfs_dirent * sd, struct dentry * parent)
 
 	if (dentry) {
 		spin_lock(&dentry->d_lock);
-		if (!(d_unhashed(dentry) && dentry->d_inode)) {
+		if (!d_unhashed(dentry) && dentry->d_inode) {
 			dget_dlock(dentry);
 			__d_drop(dentry);
 			spin_unlock(&dentry->d_lock);

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