linux-kernel - [PATCH 4.9 26/32] ceph: fix use-after-free on symlink traversal

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Message-Id: <20190502143321.995648054@linuxfoundation.org>
Date:   Thu,  2 May 2019 17:21:12 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Al Viro <viro@...iv.linux.org.uk>,
        Jeff Layton <jlayton@...nel.org>,
        Ilya Dryomov <idryomov@...il.com>,
        "Sasha Levin (Microsoft)" <sashal@...nel.org>
Subject: [PATCH 4.9 26/32] ceph: fix use-after-free on symlink traversal

[ Upstream commit daf5cc27eed99afdea8d96e71b89ba41f5406ef6 ]

free the symlink body after the same RCU delay we have for freeing the
struct inode itself, so that traversal during RCU pathwalk wouldn't step
into freed memory.

Signed-off-by: Al Viro <viro@...iv.linux.org.uk>
Reviewed-by: Jeff Layton <jlayton@...nel.org>
Signed-off-by: Ilya Dryomov <idryomov@...il.com>
Signed-off-by: Sasha Levin (Microsoft) <sashal@...nel.org>
---
 fs/ceph/inode.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/ceph/inode.c b/fs/ceph/inode.c
index 30d9d9e7057d..7a4052501866 100644
--- a/fs/ceph/inode.c
+++ b/fs/ceph/inode.c
@@ -523,6 +523,7 @@ static void ceph_i_callback(struct rcu_head *head)
 	struct inode *inode = container_of(head, struct inode, i_rcu);
 	struct ceph_inode_info *ci = ceph_inode(inode);
 
+	kfree(ci->i_symlink);
 	kmem_cache_free(ceph_inode_cachep, ci);
 }
 
@@ -554,7 +555,6 @@ void ceph_destroy_inode(struct inode *inode)
 		ceph_put_snap_realm(mdsc, realm);
 	}
 
-	kfree(ci->i_symlink);
 	while ((n = rb_first(&ci->i_fragtree)) != NULL) {
 		frag = rb_entry(n, struct ceph_inode_frag, node);
 		rb_erase(n, &ci->i_fragtree);
-- 
2.19.1