[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>

7 files changed, 110 insertions, 44 deletions

diff --git a/include/linux/security.h b/include/linux/security.h
index f75303831d09..aa5b8043dc38 100644
--- a/include/linux/security.h
+++ b/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;
 }
diff --git a/include/net/af_unix.h b/include/net/af_unix.h
index 2fec827c8801..c0398f5a8cb9 100644
--- a/include/net/af_unix.h
+++ b/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)
diff --git a/include/net/scm.h b/include/net/scm.h
index 02daa097cdcd..5637d5e22d5f 100644
--- a/include/net/scm.h
+++ b/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)
diff --git a/net/ipv4/ip_sockglue.c b/net/ipv4/ip_sockglue.c
index 84f43a3c9098..2d05c4133d3e 100644
--- a/net/ipv4/ip_sockglue.c
+++ b/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);
 }
 
 
diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
index 6f2909279268..de6ec519272e 100644
--- a/net/unix/af_unix.c
+++ b/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);
diff --git a/security/dummy.c b/security/dummy.c
index bbbfda70e131..58c6d399c844 100644
--- a/security/dummy.c
+++ b/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);
diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index a91c961ba38b..5d1b8c733199 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -3524,25 +3524,21 @@ out:
         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,