[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>

2 files changed, 36 insertions, 16 deletions

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,