apparmorfs: fix use-after-free on symlink traversal

BugLink: https://bugs.launchpad.net/bugs/1838576
[ 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>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>

diff --git a/security/apparmor/apparmorfs.c b/security/apparmor/apparmorfs.c
index b7206af5b7b7b8f863d0ef97b9d5114f328bda52..5386fe3bf88c847f1529a52dcd898b528dd4512d 100644 (file)
--- 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,
 };