[PATCH AUTOSEL 4.19 10/25] securityfs: fix use-after-free on symlink traversal

[Sasha Levin]

From: Al Viro <viro@xxxxxxxxxxxxxxxxxx>

[ 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@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 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