net/unix: support SCM_SECURITY for stream sockets

SCM_SECURITY was originally only implemented for datagram sockets,
not for stream sockets.  However, SCM_CREDENTIALS is supported on
Unix stream sockets.  For consistency, implement Unix stream support
for SCM_SECURITY as well.  Also clean up the existing code and get
rid of the superfluous UNIXSID macro.

Motivated by https://bugzilla.redhat.com/show_bug.cgi?id=1224211,
where systemd was using SCM_CREDENTIALS and assumed wrongly that
SCM_SECURITY was also supported on Unix stream sockets.

Signed-off-by: Stephen Smalley <sds@tycho.nsa.gov>
Acked-by: Paul Moore <paul@paul-moore.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 16 insertions, 4 deletions

diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
index f25e1675b865..03ee4d359f6a 100644
--- a/net/unix/af_unix.c
+++ b/net/unix/af_unix.c
@@ -140,12 +140,17 @@ static struct hlist_head *unix_sockets_unbound(void *addr)
 #ifdef CONFIG_SECURITY_NETWORK
 static void unix_get_secdata(struct scm_cookie *scm, struct sk_buff *skb)
 {
-        memcpy(UNIXSID(skb), &scm->secid, sizeof(u32));
+        UNIXCB(skb).secid = scm->secid;
 }
 
 static inline void unix_set_secdata(struct scm_cookie *scm, struct sk_buff *skb)
 {
-        scm->secid = *UNIXSID(skb);
+        scm->secid = UNIXCB(skb).secid;
+}
+
+static inline bool unix_secdata_eq(struct scm_cookie *scm, struct sk_buff *skb)
+{
+        return (scm->secid == UNIXCB(skb).secid);
 }
 #else
 static inline void unix_get_secdata(struct scm_cookie *scm, struct sk_buff *skb)
@@ -153,6 +158,11 @@ 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)
 { }
+
+static inline bool unix_secdata_eq(struct scm_cookie *scm, struct sk_buff *skb)
+{
+        return true;
+}
 #endif /* CONFIG_SECURITY_NETWORK */
 
 /*
@@ -1414,6 +1424,7 @@ static int unix_scm_to_skb(struct scm_cookie *scm, struct sk_buff *skb, bool sen
         UNIXCB(skb).uid = scm->creds.uid;
         UNIXCB(skb).gid = scm->creds.gid;
         UNIXCB(skb).fp = NULL;
+        unix_get_secdata(scm, skb);
         if (scm->fp && send_fds)
                 err = unix_attach_fds(scm, skb);
 
@@ -1509,7 +1520,6 @@ static int unix_dgram_sendmsg(struct socket *sock, struct msghdr *msg,
         if (err < 0)
                 goto out_free;
         max_level = err + 1;
-        unix_get_secdata(&scm, skb);
 
         skb_put(skb, len - data_len);
         skb->data_len = data_len;
@@ -2118,11 +2128,13 @@ unlock:
                         /* Never glue messages from different writers */
                         if ((UNIXCB(skb).pid  != scm.pid) ||
                             !uid_eq(UNIXCB(skb).uid, scm.creds.uid) ||
-                            !gid_eq(UNIXCB(skb).gid, scm.creds.gid))
+                            !gid_eq(UNIXCB(skb).gid, scm.creds.gid) ||
+                            !unix_secdata_eq(&scm, skb))
                                 break;
                 } else if (test_bit(SOCK_PASSCRED, &sock->flags)) {
                         /* Copy credentials */
                         scm_set_cred(&scm, UNIXCB(skb).pid, UNIXCB(skb).uid, UNIXCB(skb).gid);
+                        unix_set_secdata(&scm, skb);
                         check_creds = true;
                 }