[PATCH 4.14 63/77] apparmorfs: fix use-after-free on symlink traversal

Greg Kroah-Hartman
2019-05-23T19:46:59Z

[ Upstream commit f51dcd0f621caac5380ce90fbbeafc32ce4517ae ]

symlink body shouldn't be freed without an RCU delay. Switch apparmorfs
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/apparmor/apparmorfs.c | 13 +++++++++----
1 file changed, 9 insertions(+), 4 deletions(-)

diff --git a/security/apparmor/apparmorfs.c b/security/apparmor/apparmorfs.c
index 0e03377bb83ea..dd746bd69a9b2 100644
--- a/security/apparmor/apparmorfs.c
+++ b/security/apparmor/apparmorfs.c
@@ -126,17 +126,22 @@ static int aafs_show_path(struct seq_file *seq, struct dentry *dentry)
return 0;
}

-static void aafs_evict_inode(struct inode *inode)
+static void aafs_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 aafs_destroy_inode(struct inode *inode)
+{
+ call_rcu(&inode->i_rcu, aafs_i_callback);
}

static const struct super_operations aafs_super_ops = {
.statfs = simple_statfs,
- .evict_inode = aafs_evict_inode,
+ .destroy_inode = aafs_destroy_inode,
.show_path = aafs_show_path,
};

--
2.20.1