[PATCH 4.14 62/77] securityfs: fix use-after-free on symlink traversal

Greg Kroah-Hartman
2019-05-23T19:14:02Z

[ Upstream commit 46c874419652bbefdfed17420fd6e88d8a31d9ec ]

symlink body shouldn't be freed without an RCU delay. Switch securityfs
to ->destroy_inode() and use of call_rcu(); free both the inode and symlink
body in the callback.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
security/inode.c | 13 +++++++++----
1 file changed, 9 insertions(+), 4 deletions(-)

diff --git a/security/inode.c b/security/inode.c
index 8dd9ca8848e43..829f15672e01f 100644
--- a/security/inode.c
+++ b/security/inode.c
@@ -26,17 +26,22 @@
static struct vfsmount *mount;
static int mount_count;

-static void securityfs_evict_inode(struct inode *inode)
+static void securityfs_i_callback(struct rcu_head *head)
{
- truncate_inode_pages_final(&inode->i_data);
- clear_inode(inode);
+ struct inode *inode = container_of(head, struct inode, i_rcu);
if (S_ISLNK(inode->i_mode))
kfree(inode->i_link);
+ free_inode_nonrcu(inode);
+}
+
+static void securityfs_destroy_inode(struct inode *inode)
+{
+ call_rcu(&inode->i_rcu, securityfs_i_callback);
}

static const struct super_operations securityfs_super_operations = {
.statfs = simple_statfs,
- .evict_inode = securityfs_evict_inode,
+ .destroy_inode = securityfs_destroy_inode,
};

static int fill_super(struct super_block *sb, void *data, int silent)
--
2.20.1