[PATCH v3] selinux: avoid sk_socket dereference in selinux_sctp_bind_connect()

[Tristan Madani <tristmd@gmail.com>]

From: Tristan Madani <tristan@talencesecurity.com>

selinux_sctp_bind_connect() dereferences sk->sk_socket to pass a
struct socket * to selinux_socket_bind() and
selinux_socket_connect_helper().  However, when the hook is invoked
from the ASCONF softirq path (sctp_process_asconf), there is no file
reference guaranteeing that sk->sk_socket is non-NULL.  The setsockopt
callers (bindx, connectx, set_primary, sendmsg connect) hold a file
reference and are not affected.

Both selinux_socket_bind() and selinux_socket_connect_helper()
immediately resolve sock->sk, never using the struct socket * for
anything else.  Refactor the inner logic into helpers that take a
struct sock * directly so that selinux_sctp_bind_connect() never needs
to touch sk->sk_socket at all.

Suggested-by: Stephen Smalley <stephen.smalley.work@gmail.com>
Fixes: d452930fd3b9 ("selinux: Add SCTP support")
Cc: stable@vger.kernel.org
Signed-off-by: Tristan Madani <tristan@talencesecurity.com>
---
Changes in v3:
  - Keep comment describing IPv4/IPv6 address processing loop
    (Stephen Smalley).

Changes in v2:
  - Refactor selinux_socket_bind() and selinux_socket_connect_helper()
    into sk-based inner helpers instead of adding a NULL check on
    sk->sk_socket (Stephen Smalley).

 security/selinux/hooks.c | 19 ++++++++++---------
 1 file changed, 10 insertions(+), 9 deletions(-)

diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index fc926d3..1f202f6 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -4689,9 +4689,8 @@ static int selinux_socket_socketpair(struct socket *socka,
    Need to determine whether we should perform a name_bind
    permission check between the socket and the port number. */
 
-static int selinux_socket_bind(struct socket *sock, struct sockaddr *address, int addrlen)
+static int __selinux_socket_bind(struct sock *sk, struct sockaddr *address, int addrlen)
 {
-	struct sock *sk = sock->sk;
 	struct sk_security_struct *sksec = selinux_sock(sk);
 	u16 family;
 	int err;
@@ -4825,13 +4824,17 @@ err_af:
 	return -EAFNOSUPPORT;
 }
 
+static int selinux_socket_bind(struct socket *sock, struct sockaddr *address, int addrlen)
+{
+	return __selinux_socket_bind(sock->sk, address, addrlen);
+}
+
 /* This supports connect(2) and SCTP connect services such as sctp_connectx(3)
  * and sctp_sendmsg(3) as described in Documentation/security/SCTP.rst
  */
-static int selinux_socket_connect_helper(struct socket *sock,
+static int selinux_socket_connect_helper(struct sock *sk,
 					 struct sockaddr *address, int addrlen)
 {
-	struct sock *sk = sock->sk;
 	struct sk_security_struct *sksec = selinux_sock(sk);
 	int err;
 
@@ -4924,7 +4927,7 @@ static int selinux_socket_connect(struct socket *sock,
 	int err;
 	struct sock *sk = sock->sk;
 
-	err = selinux_socket_connect_helper(sock, address, addrlen);
+	err = selinux_socket_connect_helper(sk, address, addrlen);
 	if (err)
 		return err;
 
@@ -5409,13 +5412,11 @@ static int selinux_sctp_bind_connect(struct sock *sk, int optname,
 	int len, err = 0, walk_size = 0;
 	void *addr_buf;
 	struct sockaddr *addr;
-	struct socket *sock;
 
 	if (!selinux_policycap_extsockclass())
 		return 0;
 
 	/* Process one or more addresses that may be IPv4 or IPv6 */
-	sock = sk->sk_socket;
 	addr_buf = address;
 
 	while (walk_size < addrlen) {
@@ -5444,14 +5445,14 @@ static int selinux_sctp_bind_connect(struct sock *sk, int optname,
 		case SCTP_PRIMARY_ADDR:
 		case SCTP_SET_PEER_PRIMARY_ADDR:
 		case SCTP_SOCKOPT_BINDX_ADD:
-			err = selinux_socket_bind(sock, addr, len);
+			err = __selinux_socket_bind(sk, addr, len);
 			break;
 		/* Connect checks */
 		case SCTP_SOCKOPT_CONNECTX:
 		case SCTP_PARAM_SET_PRIMARY:
 		case SCTP_PARAM_ADD_IP:
 		case SCTP_SENDMSG_CONNECT:
-			err = selinux_socket_connect_helper(sock, addr, len);
+			err = selinux_socket_connect_helper(sk, addr, len);
 			if (err)
 				return err;
 
-- 
2.47.3