[PATCH 4.4 20/88] exportfs: do not read dentry after free

Greg Kroah-Hartman
2018-12-14T12:22:47Z

[ Upstream commit 2084ac6c505a58f7efdec13eba633c6aaa085ca5 ]

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>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
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 714cd37a6ba3..6599c6124552 100644
--- a/fs/exportfs/expfs.c
+++ b/fs/exportfs/expfs.c
@@ -76,7 +76,7 @@ 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;
}
--
2.19.1