netdev - Re: Consequences of commit 16e5726269611b71c930054ffe9b858c1cea88eb

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Date:	Fri, 13 Jan 2012 06:50:47 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Bart Van Assche <bvanassche@....org>
Cc:	netdev@...r.kernel.org, "David S. Miller" <davem@...emloft.net>,
	Mike Christie <michaelc@...wisc.edu>,
	Eric Paris <eparis@...hat.com>
Subject: Re: Consequences of commit 16e5726269611b71c930054ffe9b858c1cea88eb

Le jeudi 12 janvier 2012 à 21:59 +0100, Eric Dumazet a écrit :
> Le jeudi 12 janvier 2012 à 19:14 +0000, Bart Van Assche a écrit :
> > Hi,
> > 
> > If my analysis is correct commit
> > 16e5726269611b71c930054ffe9b858c1cea88eb ("af_unix: dont send
> > SCM_CREDENTIALS by default") changes the value of
> > NETLINK_CREDS(skb)->pid from the sender pid into zero. Does that mean
> > that the code using that construct did work in kernel 3.1 but that it
> > is broken in kernel 3.2 ? Should that commit be reverted or will
> > someone fix the code that uses NETLINK_CREDS() ? Would changing
> > NETLINK_CREDS(skb)->pid into NETLINK_CB(skb).pid be sufficient ?
> > 
> > Thanks,
> > 
> > Bart.
> > 
> > $ git grep 'NETLINK_CREDS([a-zA-Z0-9_]*)->pid'
> > drivers/scsi/scsi_netlink.c:	pid = NETLINK_CREDS(skb)->pid;
> > kernel/audit.c:	pid  = NETLINK_CREDS(skb)->pid;
> 
> 
> What is your problem exactly ?
> 
> 

So the underlying question is : should netlink_sendmsg() always include
credentials of the sender, or should the sender use the right API for
that.

If we include a default credential, we still allow the sender to
override it.

Probably netlink is not performance sensitive so following patch could
address the problem ?

I am still not sure its really needed.

Comments ?

diff --git a/include/net/scm.h b/include/net/scm.h
index d456f4c..4af5f90 100644
--- a/include/net/scm.h
+++ b/include/net/scm.h
@@ -71,9 +71,13 @@ static __inline__ void scm_destroy(struct scm_cookie *scm)
 }
 
 static __inline__ int scm_send(struct socket *sock, struct msghdr *msg,
-			       struct scm_cookie *scm)
+			       struct scm_cookie *scm, bool populate)
 {
 	memset(scm, 0, sizeof(*scm));
+
+	if (populate)
+		scm_set_cred(scm, task_tgid(current), current_cred());
+
 	unix_get_peersec_dgram(sock, scm);
 	if (msg->msg_controllen <= 0)
 		return 0;
diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c
index 629b061..c040277 100644
--- a/net/netlink/af_netlink.c
+++ b/net/netlink/af_netlink.c
@@ -1323,7 +1323,7 @@ static int netlink_sendmsg(struct kiocb *kiocb, struct socket *sock,
 	if (NULL == siocb->scm)
 		siocb->scm = &scm;
 
-	err = scm_send(sock, msg, siocb->scm);
+	err = scm_send(sock, msg, siocb->scm, true);
 	if (err < 0)
 		return err;
 
diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
index aad8fb6..f788eb9 100644
--- a/net/unix/af_unix.c
+++ b/net/unix/af_unix.c
@@ -1438,7 +1438,7 @@ static int unix_dgram_sendmsg(struct kiocb *kiocb, struct socket *sock,
 	if (NULL == siocb->scm)
 		siocb->scm = &tmp_scm;
 	wait_for_unix_gc();
-	err = scm_send(sock, msg, siocb->scm);
+	err = scm_send(sock, msg, siocb->scm, false);
 	if (err < 0)
 		return err;
 
@@ -1599,7 +1599,7 @@ static int unix_stream_sendmsg(struct kiocb *kiocb, struct socket *sock,
 	if (NULL == siocb->scm)
 		siocb->scm = &tmp_scm;
 	wait_for_unix_gc();
-	err = scm_send(sock, msg, siocb->scm);
+	err = scm_send(sock, msg, siocb->scm, false);
 	if (err < 0)
 		return err;
 


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