From ac551b1f500b99ab05fb7ade8ba61fd61f3cfbe7 Mon Sep 17 00:00:00 2001
From: Chen Zhongjin <chenzhongjin@huawei.com>
Date: Mon, 28 Nov 2022 11:33:05 +0100
Subject: [PATCH] ovl: fix use inode directly in rcu-walk mode
commit 672e4268b2863d7e4978dfed29552b31c2f9bd4e upstream.
ovl_dentry_revalidate_common() can be called in rcu-walk mode. As document
said, "in rcu-walk mode, d_parent and d_inode should not be used without
care".
Check inode here to protect access under rcu-walk mode.
Fixes: bccece1ead36 ("ovl: allow remote upper")
Reported-and-tested-by: syzbot+a4055c78774bbf3498bb@syzkaller.appspotmail.com
Signed-off-by: Chen Zhongjin <chenzhongjin@huawei.com>
Cc: <stable@vger.kernel.org> # v5.7
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
fs/overlayfs/super.c | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)
diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
index a29a8afe9b262..3d14a3f1465d1 100644
--- a/fs/overlayfs/super.c
+++ b/fs/overlayfs/super.c
@@ -139,11 +139,16 @@ static int ovl_dentry_revalidate_common(struct dentry *dentry,
unsigned int flags, bool weak)
{
struct ovl_entry *oe = dentry->d_fsdata;
+ struct inode *inode = d_inode_rcu(dentry);
struct dentry *upper;
unsigned int i;
int ret = 1;
- upper = ovl_dentry_upper(dentry);
+ /* Careful in RCU mode */
+ if (!inode)
+ return -ECHILD;
+
+ upper = ovl_i_dentry_upper(inode);
if (upper)
ret = ovl_revalidate_real(upper, flags, weak);
--
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