[RFC PATCH 1/1] lsm: Add hook unix_path_connect

[Justin Suess <utilityemal77@gmail.com>]

Adds an LSM hook unix_path_connect.

This hook is called to check the path of a named unix socket before a
connection is initiated.

Signed-off-by: Justin Suess <utilityemal77@gmail.com>
Cc: Günther Noack <gnoack3000@gmail.com>
---
 include/linux/lsm_hook_defs.h |  1 +
 include/linux/security.h      |  6 ++++++
 net/unix/af_unix.c            |  8 ++++++++
 security/security.c           | 16 ++++++++++++++++
 4 files changed, 31 insertions(+)

diff --git a/include/linux/lsm_hook_defs.h b/include/linux/lsm_hook_defs.h
index 8c42b4bde09c..a42d1aaf3b8a 100644
--- a/include/linux/lsm_hook_defs.h
+++ b/include/linux/lsm_hook_defs.h
@@ -318,6 +318,7 @@ LSM_HOOK(int, 0, watch_key, struct key *key)
 #endif /* CONFIG_SECURITY && CONFIG_KEY_NOTIFICATIONS */
 
 #ifdef CONFIG_SECURITY_NETWORK
+LSM_HOOK(int, 0, unix_path_connect, const struct path *path)
 LSM_HOOK(int, 0, unix_stream_connect, struct sock *sock, struct sock *other,
 	 struct sock *newsk)
 LSM_HOOK(int, 0, unix_may_send, struct socket *sock, struct socket *other)
diff --git a/include/linux/security.h b/include/linux/security.h
index 83a646d72f6f..ab66f22f7e5a 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -1638,6 +1638,7 @@ static inline int security_watch_key(struct key *key)
 
 #ifdef CONFIG_SECURITY_NETWORK
 
+int security_unix_path_connect(const struct path *path);
 int security_netlink_send(struct sock *sk, struct sk_buff *skb);
 int security_unix_stream_connect(struct sock *sock, struct sock *other, struct sock *newsk);
 int security_unix_may_send(struct socket *sock,  struct socket *other);
@@ -1699,6 +1700,11 @@ static inline int security_netlink_send(struct sock *sk, struct sk_buff *skb)
 	return 0;
 }
 
+static inline int security_unix_path_connect(const struct path *path)
+{
+	return 0;
+}
+
 static inline int security_unix_stream_connect(struct sock *sock,
 					       struct sock *other,
 					       struct sock *newsk)
diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
index 55cdebfa0da0..af1a6083a69b 100644
--- a/net/unix/af_unix.c
+++ b/net/unix/af_unix.c
@@ -1226,6 +1226,14 @@ static struct sock *unix_find_bsd(struct sockaddr_un *sunaddr, int addr_len,
 	if (!S_ISSOCK(inode->i_mode))
 		goto path_put;
 
+	/*
+	 * We call the hook because we know that the inode is a socket
+	 * and we hold a valid reference to it via the path.
+	 */
+	err = security_unix_path_connect(&path);
+	if (err)
+		goto path_put;
+
 	sk = unix_find_socket_byinode(inode);
 	if (!sk)
 		goto path_put;
diff --git a/security/security.c b/security/security.c
index 31a688650601..17af5d0ddf28 100644
--- a/security/security.c
+++ b/security/security.c
@@ -4047,6 +4047,22 @@ int security_unix_stream_connect(struct sock *sock, struct sock *other,
 }
 EXPORT_SYMBOL(security_unix_stream_connect);
 
+/*
+ * security_unix_path_connect() - Check if a named AF_UNIX socket can connect
+ * @path: Path of the socket being connected to
+ *
+ * This hook is called to check permissions before connecting to a named
+ * AF_UNIX socket. This is necessary because it was not possible to check the
+ * VFS inode of the target socket before the connection is made.
+ *
+ * Return: Returns 0 if permission is granted.
+ */
+int security_unix_path_connect(const struct path *path)
+{
+	return call_int_hook(unix_path_connect, path);
+}
+EXPORT_SYMBOL(security_unix_path_connect);
+
 /**
  * security_unix_may_send() - Check if AF_UNIX socket can send datagrams
  * @sock: originating sock
-- 
2.51.0