af_unix: Allow credentials to work across user and pid namespaces.

In unix_skb_parms store pointers to struct pid and struct cred instead
of raw uid, gid, and pid values, then translate the credentials on
reception into values that are meaningful in the receiving processes
namespaces.

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

1 files changed, 31 insertions, 22 deletions

diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
index e1f1349fae86..5fe9d6fe08b8 100644
--- a/net/unix/af_unix.c
+++ b/net/unix/af_unix.c
@@ -1316,18 +1316,20 @@ static void unix_detach_fds(struct scm_cookie *scm, struct sk_buff *skb)
         int i;
 
         scm->fp = UNIXCB(skb).fp;
-        skb->destructor = sock_wfree;
         UNIXCB(skb).fp = NULL;
 
         for (i = scm->fp->count-1; i >= 0; i--)
                 unix_notinflight(scm->fp->fp[i]);
 }
 
-static void unix_destruct_fds(struct sk_buff *skb)
+static void unix_destruct_scm(struct sk_buff *skb)
 {
         struct scm_cookie scm;
         memset(&scm, 0, sizeof(scm));
-        unix_detach_fds(&scm, skb);
+        scm.pid  = UNIXCB(skb).pid;
+        scm.cred = UNIXCB(skb).cred;
+        if (UNIXCB(skb).fp)
+                unix_detach_fds(&scm, skb);
 
         /* Alas, it calls VFS */
         /* So fscking what? fput() had been SMP-safe since the last Summer */
@@ -1350,10 +1352,22 @@ static int unix_attach_fds(struct scm_cookie *scm, struct sk_buff *skb)
 
         for (i = scm->fp->count-1; i >= 0; i--)
                 unix_inflight(scm->fp->fp[i]);
-        skb->destructor = unix_destruct_fds;
         return 0;
 }
 
+static int unix_scm_to_skb(struct scm_cookie *scm, struct sk_buff *skb, bool send_fds)
+{
+        int err = 0;
+        UNIXCB(skb).pid  = get_pid(scm->pid);
+        UNIXCB(skb).cred = get_cred(scm->cred);
+        UNIXCB(skb).fp = NULL;
+        if (scm->fp && send_fds)
+                err = unix_attach_fds(scm, skb);
+
+        skb->destructor = unix_destruct_scm;
+        return err;
+}
+
 /*
  *      Send AF_UNIX data.
  */
@@ -1410,12 +1424,9 @@ static int unix_dgram_sendmsg(struct kiocb *kiocb, struct socket *sock,
         if (skb == NULL)
                 goto out;
 
-        memcpy(UNIXCREDS(skb), &siocb->scm->creds, sizeof(struct ucred));
-        if (siocb->scm->fp) {
-                err = unix_attach_fds(siocb->scm, skb);
-                if (err)
-                        goto out_free;
-        }
+        err = unix_scm_to_skb(siocb->scm, skb, true);
+        if (err)
+                goto out_free;
         unix_get_secdata(siocb->scm, skb);
 
         skb_reset_transport_header(skb);
@@ -1585,16 +1596,14 @@ static int unix_stream_sendmsg(struct kiocb *kiocb, struct socket *sock,
                  */
                 size = min_t(int, size, skb_tailroom(skb));
 
-                memcpy(UNIXCREDS(skb), &siocb->scm->creds, sizeof(struct ucred));
+
                 /* Only send the fds in the first buffer */
-                if (siocb->scm->fp && !fds_sent) {
-                        err = unix_attach_fds(siocb->scm, skb);
-                        if (err) {
-                                kfree_skb(skb);
-                                goto out_err;
-                        }
-                        fds_sent = true;
+                err = unix_scm_to_skb(siocb->scm, skb, !fds_sent);
+                if (err) {
+                        kfree_skb(skb);
+                        goto out_err;
                 }
+                fds_sent = true;
 
                 err = memcpy_fromiovec(skb_put(skb, size), msg->msg_iov, size);
                 if (err) {
@@ -1711,7 +1720,7 @@ static int unix_dgram_recvmsg(struct kiocb *iocb, struct socket *sock,
                 siocb->scm = &tmp_scm;
                 memset(&tmp_scm, 0, sizeof(tmp_scm));
         }
-        siocb->scm->creds = *UNIXCREDS(skb);
+        scm_set_cred(siocb->scm, UNIXCB(skb).pid, UNIXCB(skb).cred);
         unix_set_secdata(siocb->scm, skb);
 
         if (!(flags & MSG_PEEK)) {
@@ -1860,14 +1869,14 @@ static int unix_stream_recvmsg(struct kiocb *iocb, struct socket *sock,
 
                 if (check_creds) {
                         /* Never glue messages from different writers */
-                        if (memcmp(UNIXCREDS(skb), &siocb->scm->creds,
-                                   sizeof(siocb->scm->creds)) != 0) {
+                        if ((UNIXCB(skb).pid  != siocb->scm->pid) ||
+                            (UNIXCB(skb).cred != siocb->scm->cred)) {
                                 skb_queue_head(&sk->sk_receive_queue, skb);
                                 break;
                         }
                 } else {
                         /* Copy credentials */
-                        siocb->scm->creds = *UNIXCREDS(skb);
+                        scm_set_cred(siocb->scm, UNIXCB(skb).pid, UNIXCB(skb).cred);
                         check_creds = 1;
                 }