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Commit 16e57262 authored by Eric Dumazet's avatar Eric Dumazet Committed by David S. Miller
Browse files

af_unix: dont send SCM_CREDENTIALS by default 



Since commit 7361c36c (af_unix: Allow credentials to work across
user and pid namespaces) af_unix performance dropped a lot.

This is because we now take a reference on pid and cred in each write(),
and release them in read(), usually done from another process,
eventually from another cpu. This triggers false sharing.

# Events: 154K cycles
#
# Overhead  Command       Shared Object        Symbol
# ........  .......  ..................  .........................
#
    10.40%  hackbench  [kernel.kallsyms]   [k] put_pid
     8.60%  hackbench  [kernel.kallsyms]   [k] unix_stream_recvmsg
     7.87%  hackbench  [kernel.kallsyms]   [k] unix_stream_sendmsg
     6.11%  hackbench  [kernel.kallsyms]   [k] do_raw_spin_lock
     4.95%  hackbench  [kernel.kallsyms]   [k] unix_scm_to_skb
     4.87%  hackbench  [kernel.kallsyms]   [k] pid_nr_ns
     4.34%  hackbench  [kernel.kallsyms]   [k] cred_to_ucred
     2.39%  hackbench  [kernel.kallsyms]   [k] unix_destruct_scm
     2.24%  hackbench  [kernel.kallsyms]   [k] sub_preempt_count
     1.75%  hackbench  [kernel.kallsyms]   [k] fget_light
     1.51%  hackbench  [kernel.kallsyms]   [k]
__mutex_lock_interruptible_slowpath
     1.42%  hackbench  [kernel.kallsyms]   [k] sock_alloc_send_pskb

This patch includes SCM_CREDENTIALS information in a af_unix message/skb
only if requested by the sender, [man 7 unix for details how to include
ancillary data using sendmsg() system call]

Note: This might break buggy applications that expected SCM_CREDENTIAL
from an unaware write() system call, and receiver not using SO_PASSCRED
socket option.

If SOCK_PASSCRED is set on source or destination socket, we still
include credentials for mere write() syscalls.

Performance boost in hackbench : more than 50% gain on a 16 thread
machine (2 quad-core cpus, 2 threads per core)

hackbench 20 thread 2000

4.228 sec instead of 9.102 sec

Signed-off-by: default avatarEric Dumazet <eric.dumazet@gmail.com>
Acked-by: default avatarTim Chen <tim.c.chen@linux.intel.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent a9e9fd71

include/net/scm.h

+2 −3
Original line number Diff line number Diff line
@@ -49,7 +49,7 @@ static __inline__ void scm_set_cred(struct scm_cookie *scm, 
				    struct pid *pid, const struct cred *cred)

{

	scm->pid  = get_pid(pid);

	scm->cred = get_cred(cred);

	scm->cred = cred ? get_cred(cred) : NULL;

	cred_to_ucred(pid, cred, &scm->creds);

}
@@ -73,8 +73,7 @@ static __inline__ void scm_destroy(struct scm_cookie *scm) 
static __inline__ int scm_send(struct socket *sock, struct msghdr *msg,

			       struct scm_cookie *scm)

{

	scm_set_cred(scm, task_tgid(current), current_cred());

	scm->fp = NULL;

	memset(scm, 0, sizeof(*scm));

	unix_get_peersec_dgram(sock, scm);

	if (msg->msg_controllen <= 0)

		return 0;

net/core/scm.c

+6 −4
Original line number Diff line number Diff line
@@ -173,7 +173,7 @@ int __scm_send(struct socket *sock, struct msghdr *msg, struct scm_cookie *p) 
			if (err)

				goto error;



			if (pid_vnr(p->pid) != p->creds.pid) {

			if (!p->pid || pid_vnr(p->pid) != p->creds.pid) {

				struct pid *pid;

				err = -ESRCH;

				pid = find_get_pid(p->creds.pid);
@@ -183,7 +183,8 @@ int __scm_send(struct socket *sock, struct msghdr *msg, struct scm_cookie *p) 
				p->pid = pid;

			}



			if ((p->cred->euid != p->creds.uid) ||

			if (!p->cred ||

			    (p->cred->euid != p->creds.uid) ||

			    (p->cred->egid != p->creds.gid)) {

				struct cred *cred;

				err = -ENOMEM;
@@ -193,6 +194,7 @@ int __scm_send(struct socket *sock, struct msghdr *msg, struct scm_cookie *p) 


				cred->uid = cred->euid = p->creds.uid;

				cred->gid = cred->egid = p->creds.gid;

				if (p->cred)

					put_cred(p->cred);

				p->cred = cred;

			}

net/netlink/af_netlink.c

+2 −3
Original line number Diff line number Diff line
@@ -1324,10 +1324,9 @@ static int netlink_sendmsg(struct kiocb *kiocb, struct socket *sock, 
	if (msg->msg_flags&MSG_OOB)

		return -EOPNOTSUPP;



	if (NULL == siocb->scm) {

	if (NULL == siocb->scm)

		siocb->scm = &scm;

		memset(&scm, 0, sizeof(scm));

	}



	err = scm_send(sock, msg, siocb->scm);

	if (err < 0)

		return err;

net/unix/af_unix.c

+23 −1
Original line number Diff line number Diff line
@@ -1381,7 +1381,9 @@ static int unix_attach_fds(struct scm_cookie *scm, struct sk_buff *skb) 
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);

	if (scm->cred)

		UNIXCB(skb).cred = get_cred(scm->cred);

	UNIXCB(skb).fp = NULL;

	if (scm->fp && send_fds)
@@ -1391,6 +1393,24 @@ static int unix_scm_to_skb(struct scm_cookie *scm, struct sk_buff *skb, bool sen 
	return err;

}



/*

 * Some apps rely on write() giving SCM_CREDENTIALS

 * We include credentials if source or destination socket

 * asserted SOCK_PASSCRED.

 */

static void maybe_add_creds(struct sk_buff *skb, const struct socket *sock,

			    const struct sock *other)

{

	if (UNIXCB(skb).cred)

		return;

	if (test_bit(SOCK_PASSCRED, &sock->flags) ||

	    !other->sk_socket ||

	    test_bit(SOCK_PASSCRED, &other->sk_socket->flags)) {

		UNIXCB(skb).pid  = get_pid(task_tgid(current));

		UNIXCB(skb).cred = get_current_cred();

	}

}



/*

 *	Send AF_UNIX data.

 */
@@ -1538,6 +1558,7 @@ static int unix_dgram_sendmsg(struct kiocb *kiocb, struct socket *sock, 


	if (sock_flag(other, SOCK_RCVTSTAMP))

		__net_timestamp(skb);

	maybe_add_creds(skb, sock, other);

	skb_queue_tail(&other->sk_receive_queue, skb);

	if (max_level > unix_sk(other)->recursion_level)

		unix_sk(other)->recursion_level = max_level;
@@ -1652,6 +1673,7 @@ static int unix_stream_sendmsg(struct kiocb *kiocb, struct socket *sock, 
		    (other->sk_shutdown & RCV_SHUTDOWN))

			goto pipe_err_free;



		maybe_add_creds(skb, sock, other);

		skb_queue_tail(&other->sk_receive_queue, skb);

		if (max_level > unix_sk(other)->recursion_level)

			unix_sk(other)->recursion_level = max_level;