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, 12 insertions, 6 deletions

diff --git a/net/core/sock.c b/net/core/sock.c
index db8335ad7559..0229d5566a46 100644
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -915,11 +915,15 @@ int sock_getsockopt(struct socket *sock, int level, int optname,
                 break;
 
         case SO_PEERCRED:
-                if (len > sizeof(sk->sk_peercred))
-                        len = sizeof(sk->sk_peercred);
-                if (copy_to_user(optval, &sk->sk_peercred, len))
+        {
+                struct ucred peercred;
+                if (len > sizeof(peercred))
+                        len = sizeof(peercred);
+                cred_to_ucred(sk->sk_peer_pid, sk->sk_peer_cred, &peercred);
+                if (copy_to_user(optval, &peercred, len))
                         return -EFAULT;
                 goto lenout;
+        }
 
         case SO_PEERNAME:
         {
@@ -1133,6 +1137,9 @@ static void __sk_free(struct sock *sk)
                 printk(KERN_DEBUG "%s: optmem leakage (%d bytes) detected.\n",
                        __func__, atomic_read(&sk->sk_omem_alloc));
 
+        if (sk->sk_peer_cred)
+                put_cred(sk->sk_peer_cred);
+        put_pid(sk->sk_peer_pid);
         put_net(sock_net(sk));
         sk_prot_free(sk->sk_prot_creator, sk);
 }
@@ -1968,9 +1975,8 @@ void sock_init_data(struct socket *sock, struct sock *sk)
         sk->sk_sndmsg_page      =       NULL;
         sk->sk_sndmsg_off       =       0;
 
-        sk->sk_peercred.pid     =       0;
-        sk->sk_peercred.uid     =       -1;
-        sk->sk_peercred.gid     =       -1;
+        sk->sk_peer_pid         =       NULL;
+        sk->sk_peer_cred        =       NULL;
         sk->sk_write_pending    =       0;
         sk->sk_rcvlowat         =       1;
         sk->sk_rcvtimeo         =       MAX_SCHEDULE_TIMEOUT;