af_unix: Allow SO_PEERCRED to work across namespaces.

Use struct pid and struct cred to store the peer credentials on struct
sock.  This gives enough information to convert the peer credential
information to a value relative to whatever namespace the socket is in
at the time.

This removes nasty surprises when using SO_PEERCRED on socket
connetions where the processes on either side are in different pid and
user namespaces.

Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
Acked-by: Daniel Lezcano <daniel.lezcano@free.fr>
Acked-by: Pavel Emelyanov <xemul@openvz.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 28 insertions, 9 deletions

diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
index fef2cc5e9d2..e1f1349fae8 100644
--- a/net/unix/af_unix.c
+++ b/net/unix/af_unix.c
@@ -450,11 +450,31 @@ static int unix_release_sock(struct sock *sk, int embrion)
         return 0;
 }
 
+static void init_peercred(struct sock *sk)
+{
+        put_pid(sk->sk_peer_pid);
+        if (sk->sk_peer_cred)
+                put_cred(sk->sk_peer_cred);
+        sk->sk_peer_pid  = get_pid(task_tgid(current));
+        sk->sk_peer_cred = get_current_cred();
+}
+
+static void copy_peercred(struct sock *sk, struct sock *peersk)
+{
+        put_pid(sk->sk_peer_pid);
+        if (sk->sk_peer_cred)
+                put_cred(sk->sk_peer_cred);
+        sk->sk_peer_pid  = get_pid(peersk->sk_peer_pid);
+        sk->sk_peer_cred = get_cred(peersk->sk_peer_cred);
+}
+
 static int unix_listen(struct socket *sock, int backlog)
 {
         int err;
         struct sock *sk = sock->sk;
         struct unix_sock *u = unix_sk(sk);
+        struct pid *old_pid = NULL;
+        const struct cred *old_cred = NULL;
 
         err = -EOPNOTSUPP;
         if (sock->type != SOCK_STREAM && sock->type != SOCK_SEQPACKET)
@@ -470,12 +490,14 @@ static int unix_listen(struct socket *sock, int backlog)
         sk->sk_max_ack_backlog  = backlog;
         sk->sk_state            = TCP_LISTEN;
         /* set credentials so connect can copy them */
-        sk->sk_peercred.pid     = task_tgid_vnr(current);
-        current_euid_egid(&sk->sk_peercred.uid, &sk->sk_peercred.gid);
+        init_peercred(sk);
         err = 0;
 
 out_unlock:
         unix_state_unlock(sk);
+        put_pid(old_pid);
+        if (old_cred)
+                put_cred(old_cred);
 out:
         return err;
 }
@@ -1140,8 +1162,7 @@ restart:
         unix_peer(newsk)        = sk;
         newsk->sk_state         = TCP_ESTABLISHED;
         newsk->sk_type          = sk->sk_type;
-        newsk->sk_peercred.pid  = task_tgid_vnr(current);
-        current_euid_egid(&newsk->sk_peercred.uid, &newsk->sk_peercred.gid);
+        init_peercred(newsk);
         newu = unix_sk(newsk);
         newsk->sk_wq            = &newu->peer_wq;
         otheru = unix_sk(other);
@@ -1157,7 +1178,7 @@ restart:
         }
 
         /* Set credentials */
-        sk->sk_peercred = other->sk_peercred;
+        copy_peercred(sk, other);
 
         sock->state     = SS_CONNECTED;
         sk->sk_state    = TCP_ESTABLISHED;
@@ -1199,10 +1220,8 @@ static int unix_socketpair(struct socket *socka, struct socket *sockb)
         sock_hold(skb);
         unix_peer(ska) = skb;
         unix_peer(skb) = ska;
-        ska->sk_peercred.pid = skb->sk_peercred.pid = task_tgid_vnr(current);
-        current_euid_egid(&skb->sk_peercred.uid, &skb->sk_peercred.gid);
-        ska->sk_peercred.uid = skb->sk_peercred.uid;
-        ska->sk_peercred.gid = skb->sk_peercred.gid;
+        init_peercred(ska);
+        init_peercred(skb);
 
         if (ska->sk_type != SOCK_DGRAM) {
                 ska->sk_state = TCP_ESTABLISHED;