[PATCH V2] exportfs: do not read dentry after free

From: Pan Bian <bianpan2016@163.com>
To: Amir Goldstein <amir73il@gmail.com>,
	Miklos Szeredi <mszeredi@redhat.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>,
	"J. Bruce Fields" <bfields@fieldses.org>,
	Christoph Hellwig <hch@lst.de>,
	linux-kernel <linux-kernel@vger.kernel.org>,
	Pan Bian <bianpan2016@163.com>
Subject: [PATCH V2] exportfs: do not read dentry after free
Date: Fri, 23 Nov 2018 15:56:33 +0800	[thread overview]
Message-ID: <1542959793-118334-1-git-send-email-bianpan2016@163.com> (raw)

The function dentry_connected calls dput(dentry) to drop the previously
acquired reference to dentry. In this case, dentry can be released.
After that, IS_ROOT(dentry) checks the condition
(dentry == dentry->d_parent), which may result in a use-after-free bug.
This patch directly compares dentry with its parent obtained before
dropping the reference.

Fixes: a056cc8934c("exportfs: stop retrying once we race with
rename/remove")

Signed-off-by: Pan Bian <bianpan2016@163.com>

---
V2: get rid of the comment

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

diff --git a/fs/exportfs/expfs.c b/fs/exportfs/expfs.c
index 645158d..a69aaf5 100644
--- a/fs/exportfs/expfs.c
+++ b/fs/exportfs/expfs.c
@@ -77,7 +77,7 @@ static bool dentry_connected(struct dentry *dentry)
 		struct dentry *parent = dget_parent(dentry);
 
 		dput(dentry);
-		if (IS_ROOT(dentry)) {
+		if (dentry == parent) {
 			dput(parent);
 			return false;
 		}
-- 
2.7.4


