[AF_UNIX]: Kernel memory leak fix for af_unix datagram getpeersec patch

From: Catherine Zhang <cxzhang@watson.ibm.com>

This patch implements a cleaner fix for the memory leak problem of the
original unix datagram getpeersec patch.  Instead of creating a
security context each time a unix datagram is sent, we only create the
security context when the receiver requests it.

This new design requires modification of the current
unix_getsecpeer_dgram LSM hook and addition of two new hooks, namely,
secid_to_secctx and release_secctx.  The former retrieves the security
context and the latter releases it.  A hook is required for releasing
the security context because it is up to the security module to decide
how that's done.  In the case of Selinux, it's a simple kfree
operation.
Acked-by: Stephen Smalley <sds@tycho.nsa.gov>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/security.h

@@ -1109,6 +1109,16 @@ struct swap_info_struct;
  *	@name contains the name of the security module being unstacked.
  *	@ops contains a pointer to the struct security_operations of the module to unstack.
  * 
+ * @secid_to_secctx:
+ *	Convert secid to security context.
+ *	@secid contains the security ID.
+ *	@secdata contains the pointer that stores the converted security context.
+ *
+ * @release_secctx:
+ *	Release the security context.
+ *	@secdata contains the security context.
+ *	@seclen contains the length of the security context.
+ *
  * This is the main security structure.
  */
 struct security_operations {
@@ -1289,6 +1299,8 @@ struct security_operations {
 
  	int (*getprocattr)(struct task_struct *p, char *name, void *value, size_t size);
  	int (*setprocattr)(struct task_struct *p, char *name, void *value, size_t size);
+	int (*secid_to_secctx)(u32 secid, char **secdata, u32 *seclen);
+	void (*release_secctx)(char *secdata, u32 seclen);
 
 #ifdef CONFIG_SECURITY_NETWORK
 	int (*unix_stream_connect) (struct socket * sock,
@@ -1317,7 +1329,7 @@ struct security_operations {
 	int (*socket_shutdown) (struct socket * sock, int how);
 	int (*socket_sock_rcv_skb) (struct sock * sk, struct sk_buff * skb);
 	int (*socket_getpeersec_stream) (struct socket *sock, char __user *optval, int __user *optlen, unsigned len);
-	int (*socket_getpeersec_dgram) (struct sk_buff *skb, char **secdata, u32 *seclen);
+	int (*socket_getpeersec_dgram) (struct socket *sock, struct sk_buff *skb, u32 *secid);
 	int (*sk_alloc_security) (struct sock *sk, int family, gfp_t priority);
 	void (*sk_free_security) (struct sock *sk);
 	unsigned int (*sk_getsid) (struct sock *sk, struct flowi *fl, u8 dir);
@@ -2059,6 +2071,16 @@ static inline int security_netlink_recv(struct sk_buff * skb, int cap)
 	return security_ops->netlink_recv(skb, cap);
 }
 
+static inline int security_secid_to_secctx(u32 secid, char **secdata, u32 *seclen)
+{
+	return security_ops->secid_to_secctx(secid, secdata, seclen);
+}
+
+static inline void security_release_secctx(char *secdata, u32 seclen)
+{
+	return security_ops->release_secctx(secdata, seclen);
+}
+
 /* prototypes */
 extern int security_init	(void);
 extern int register_security	(struct security_operations *ops);
@@ -2725,6 +2747,15 @@ static inline void securityfs_remove(struct dentry *dentry)
 {
 }
 
+static inline int security_secid_to_secctx(u32 secid, char **secdata, u32 *seclen)
+{
+	return -EOPNOTSUPP;
+}
+
+static inline void security_release_secctx(char *secdata, u32 seclen)
+{
+	return -EOPNOTSUPP;
+}
 #endif	/* CONFIG_SECURITY */
 
 #ifdef CONFIG_SECURITY_NETWORK
@@ -2840,10 +2871,9 @@ static inline int security_socket_getpeersec_stream(struct socket *sock, char __
 	return security_ops->socket_getpeersec_stream(sock, optval, optlen, len);
 }
 
-static inline int security_socket_getpeersec_dgram(struct sk_buff *skb, char **secdata,
-						   u32 *seclen)
+static inline int security_socket_getpeersec_dgram(struct socket *sock, struct sk_buff *skb, u32 *secid)
 {
-	return security_ops->socket_getpeersec_dgram(skb, secdata, seclen);
+	return security_ops->socket_getpeersec_dgram(sock, skb, secid);
 }
 
 static inline int security_sk_alloc(struct sock *sk, int family, gfp_t priority)
@@ -2968,8 +2998,7 @@ static inline int security_socket_getpeersec_stream(struct socket *sock, char __
 	return -ENOPROTOOPT;
 }
 
-static inline int security_socket_getpeersec_dgram(struct sk_buff *skb, char **secdata,
-						   u32 *seclen)
+static inline int security_socket_getpeersec_dgram(struct socket *sock, struct sk_buff *skb, u32 *secid)
 {
 	return -ENOPROTOOPT;
 }

include/net/af_unix.h

@@ -54,15 +54,13 @@ struct unix_skb_parms {
 	struct ucred		creds;		/* Skb credentials	*/
 	struct scm_fp_list	*fp;		/* Passed files		*/
 #ifdef CONFIG_SECURITY_NETWORK
-	char			*secdata;	/* Security context	*/
-	u32			seclen;		/* Security length	*/
+	u32			secid;		/* Security ID		*/
 #endif
 };
 
 #define UNIXCB(skb) 	(*(struct unix_skb_parms*)&((skb)->cb))
 #define UNIXCREDS(skb)	(&UNIXCB((skb)).creds)
-#define UNIXSECDATA(skb)	(&UNIXCB((skb)).secdata)
-#define UNIXSECLEN(skb)		(&UNIXCB((skb)).seclen)
+#define UNIXSID(skb)	(&UNIXCB((skb)).secid)
 
 #define unix_state_rlock(s)	spin_lock(&unix_sk(s)->lock)
 #define unix_state_runlock(s)	spin_unlock(&unix_sk(s)->lock)

include/net/scm.h

@@ -3,6 +3,7 @@
 
 #include <linux/limits.h>
 #include <linux/net.h>
+#include <linux/security.h>
 
 /* Well, we should have at least one descriptor open
  * to accept passed FDs 8)
@@ -20,8 +21,7 @@ struct scm_cookie
 	struct ucred		creds;		/* Skb credentials	*/
 	struct scm_fp_list	*fp;		/* Passed files		*/
 #ifdef CONFIG_SECURITY_NETWORK
-	char			*secdata;	/* Security context	*/
-	u32			seclen;		/* Security length	*/
+	u32			secid;		/* Passed security ID 	*/
 #endif
 	unsigned long		seq;		/* Connection seqno	*/
 };
@@ -32,6 +32,16 @@ extern int __scm_send(struct socket *sock, struct msghdr *msg, struct scm_cookie
 extern void __scm_destroy(struct scm_cookie *scm);
 extern struct scm_fp_list * scm_fp_dup(struct scm_fp_list *fpl);
 
+#ifdef CONFIG_SECURITY_NETWORK
+static __inline__ void unix_get_peersec_dgram(struct socket *sock, struct scm_cookie *scm)
+{
+	security_socket_getpeersec_dgram(sock, NULL, &scm->secid);
+}
+#else
+static __inline__ void unix_get_peersec_dgram(struct socket *sock, struct scm_cookie *scm)
+{ }
+#endif /* CONFIG_SECURITY_NETWORK */
+
 static __inline__ void scm_destroy(struct scm_cookie *scm)
 {
 	if (scm && scm->fp)
@@ -47,6 +57,7 @@ static __inline__ int scm_send(struct socket *sock, struct msghdr *msg,
 	scm->creds.pid = p->tgid;
 	scm->fp = NULL;
 	scm->seq = 0;
+	unix_get_peersec_dgram(sock, scm);
 	if (msg->msg_controllen <= 0)
 		return 0;
 	return __scm_send(sock, msg, scm);
@@ -55,8 +66,18 @@ static __inline__ int scm_send(struct socket *sock, struct msghdr *msg,
 #ifdef CONFIG_SECURITY_NETWORK
 static inline void scm_passec(struct socket *sock, struct msghdr *msg, struct scm_cookie *scm)
 {
-	if (test_bit(SOCK_PASSSEC, &sock->flags) && scm->secdata != NULL)
-		put_cmsg(msg, SOL_SOCKET, SCM_SECURITY, scm->seclen, scm->secdata);
+	char *secdata;
+	u32 seclen;
+	int err;
+
+	if (test_bit(SOCK_PASSSEC, &sock->flags)) {
+		err = security_secid_to_secctx(scm->secid, &secdata, &seclen);
+
+		if (!err) {
+			put_cmsg(msg, SOL_SOCKET, SCM_SECURITY, seclen, secdata);
+			security_release_secctx(secdata, seclen);
+		}
+	}
 }
 #else
 static inline void scm_passec(struct socket *sock, struct msghdr *msg, struct scm_cookie *scm)

net/ipv4/ip_sockglue.c

@@ -112,14 +112,19 @@ static void ip_cmsg_recv_retopts(struct msghdr *msg, struct sk_buff *skb)
 static void ip_cmsg_recv_security(struct msghdr *msg, struct sk_buff *skb)
 {
 	char *secdata;
-	u32 seclen;
+	u32 seclen, secid;
 	int err;
 
-	err = security_socket_getpeersec_dgram(skb, &secdata, &seclen);
+	err = security_socket_getpeersec_dgram(NULL, skb, &secid);
+	if (err)
+		return;
+
+	err = security_secid_to_secctx(secid, &secdata, &seclen);
 	if (err)
 		return;
 
 	put_cmsg(msg, SOL_IP, SCM_SECURITY, seclen, secdata);
+	security_release_secctx(secdata, seclen);
 }
 
 

net/unix/af_unix.c

@@ -128,23 +128,17 @@ static atomic_t unix_nr_socks = ATOMIC_INIT(0);
 #define UNIX_ABSTRACT(sk)	(unix_sk(sk)->addr->hash != UNIX_HASH_SIZE)
 
 #ifdef CONFIG_SECURITY_NETWORK
-static void unix_get_peersec_dgram(struct sk_buff *skb)
+static void unix_get_secdata(struct scm_cookie *scm, struct sk_buff *skb)
 {
-	int err;
-
-	err = security_socket_getpeersec_dgram(skb, UNIXSECDATA(skb),
-					       UNIXSECLEN(skb));
-	if (err)
-		*(UNIXSECDATA(skb)) = NULL;
+	memcpy(UNIXSID(skb), &scm->secid, sizeof(u32));
 }
 
 static inline void unix_set_secdata(struct scm_cookie *scm, struct sk_buff *skb)
 {
-	scm->secdata = *UNIXSECDATA(skb);
-	scm->seclen = *UNIXSECLEN(skb);
+	scm->secid = *UNIXSID(skb);
 }
 #else
-static inline void unix_get_peersec_dgram(struct sk_buff *skb)
+static inline void unix_get_secdata(struct scm_cookie *scm, struct sk_buff *skb)
 { }
 
 static inline void unix_set_secdata(struct scm_cookie *scm, struct sk_buff *skb)
@@ -1322,8 +1316,7 @@ static int unix_dgram_sendmsg(struct kiocb *kiocb, struct socket *sock,
 	memcpy(UNIXCREDS(skb), &siocb->scm->creds, sizeof(struct ucred));
 	if (siocb->scm->fp)
 		unix_attach_fds(siocb->scm, skb);
-
-	unix_get_peersec_dgram(skb);
+	unix_get_secdata(siocb->scm, skb);
 
 	skb->h.raw = skb->data;
 	err = memcpy_fromiovec(skb_put(skb,len), msg->msg_iov, len);

security/dummy.c

@@ -791,8 +791,7 @@ static int dummy_socket_getpeersec_stream(struct socket *sock, char __user *optv
 	return -ENOPROTOOPT;
 }
 
-static int dummy_socket_getpeersec_dgram(struct sk_buff *skb, char **secdata,
-					 u32 *seclen)
+static int dummy_socket_getpeersec_dgram(struct socket *sock, struct sk_buff *skb, u32 *secid)
 {
 	return -ENOPROTOOPT;
 }
@@ -876,6 +875,15 @@ static int dummy_setprocattr(struct task_struct *p, char *name, void *value, siz
 	return -EINVAL;
 }
 
+static int dummy_secid_to_secctx(u32 secid, char **secdata, u32 *seclen)
+{
+	return -EOPNOTSUPP;
+}
+
+static void dummy_release_secctx(char *secdata, u32 seclen)
+{
+}
+
 #ifdef CONFIG_KEYS
 static inline int dummy_key_alloc(struct key *key, struct task_struct *ctx,
 				  unsigned long flags)
@@ -1028,6 +1036,8 @@ void security_fixup_ops (struct security_operations *ops)
 	set_to_dummy_if_null(ops, d_instantiate);
  	set_to_dummy_if_null(ops, getprocattr);
  	set_to_dummy_if_null(ops, setprocattr);
+ 	set_to_dummy_if_null(ops, secid_to_secctx);
+ 	set_to_dummy_if_null(ops, release_secctx);
 #ifdef CONFIG_SECURITY_NETWORK
 	set_to_dummy_if_null(ops, unix_stream_connect);
 	set_to_dummy_if_null(ops, unix_may_send);

security/selinux/hooks.c

@@ -3524,25 +3524,21 @@ static int selinux_socket_getpeersec_stream(struct socket *sock, char __user *op
 	return err;
 }
 
-static int selinux_socket_getpeersec_dgram(struct sk_buff *skb, char **secdata, u32 *seclen)
+static int selinux_socket_getpeersec_dgram(struct socket *sock, struct sk_buff *skb, u32 *secid)
 {
+	u32 peer_secid = SECSID_NULL;
 	int err = 0;
-	u32 peer_sid;
 
-	if (skb->sk->sk_family == PF_UNIX)
-		selinux_get_inode_sid(SOCK_INODE(skb->sk->sk_socket),
-				      &peer_sid);
-	else
-		peer_sid = selinux_socket_getpeer_dgram(skb);
-
-	if (peer_sid == SECSID_NULL)
-		return -EINVAL;
+	if (sock && (sock->sk->sk_family == PF_UNIX))
+		selinux_get_inode_sid(SOCK_INODE(sock), &peer_secid);
+	else if (skb)
+		peer_secid = selinux_socket_getpeer_dgram(skb);
 
-	err = security_sid_to_context(peer_sid, secdata, seclen);
-	if (err)
-		return err;
+	if (peer_secid == SECSID_NULL)
+		err = -EINVAL;
+	*secid = peer_secid;
 
-	return 0;
+	return err;
 }
 
 static int selinux_sk_alloc_security(struct sock *sk, int family, gfp_t priority)
@@ -4407,6 +4403,17 @@ static int selinux_setprocattr(struct task_struct *p,
 	return size;
 }
 
+static int selinux_secid_to_secctx(u32 secid, char **secdata, u32 *seclen)
+{
+	return security_sid_to_context(secid, secdata, seclen);
+}
+
+static void selinux_release_secctx(char *secdata, u32 seclen)
+{
+	if (secdata)
+		kfree(secdata);
+}
+
 #ifdef CONFIG_KEYS
 
 static int selinux_key_alloc(struct key *k, struct task_struct *tsk,
@@ -4587,6 +4594,9 @@ static struct security_operations selinux_ops = {
 	.getprocattr =                  selinux_getprocattr,
 	.setprocattr =                  selinux_setprocattr,
 
+	.secid_to_secctx =		selinux_secid_to_secctx,
+	.release_secctx =		selinux_release_secctx,
+
         .unix_stream_connect =		selinux_socket_unix_stream_connect,
 	.unix_may_send =		selinux_socket_unix_may_send,