From: Pan Bian <bianpan2016@163.com>
Date: Fri, 23 Nov 2018 07:56:33 +0000 (+0800)
Subject: exportfs: do not read dentry after free
X-Git-Url: http://git.maquefel.me/?a=commitdiff_plain;h=2084ac6c505a58f7efdec13eba633c6aaa085ca5;p=linux.git

exportfs: do not read dentry after free

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>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
---

diff --git a/fs/exportfs/expfs.c b/fs/exportfs/expfs.c
index c8a3dfda17646..c69927bed4eff 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;
 		}