linux/net
Ulrich Drepper de11defebf reintroduce accept4
Introduce a new accept4() system call.  The addition of this system call
matches analogous changes in 2.6.27 (dup3(), evenfd2(), signalfd4(),
inotify_init1(), epoll_create1(), pipe2()) which added new system calls
that differed from analogous traditional system calls in adding a flags
argument that can be used to access additional functionality.

The accept4() system call is exactly the same as accept(), except that
it adds a flags bit-mask argument.  Two flags are initially implemented.
(Most of the new system calls in 2.6.27 also had both of these flags.)

SOCK_CLOEXEC causes the close-on-exec (FD_CLOEXEC) flag to be enabled
for the new file descriptor returned by accept4().  This is a useful
security feature to avoid leaking information in a multithreaded
program where one thread is doing an accept() at the same time as
another thread is doing a fork() plus exec().  More details here:
http://udrepper.livejournal.com/20407.html "Secure File Descriptor Handling",
Ulrich Drepper).

The other flag is SOCK_NONBLOCK, which causes the O_NONBLOCK flag
to be enabled on the new open file description created by accept4().
(This flag is merely a convenience, saving the use of additional calls
fcntl(F_GETFL) and fcntl (F_SETFL) to achieve the same result.

Here's a test program.  Works on x86-32.  Should work on x86-64, but
I (mtk) don't have a system to hand to test with.

It tests accept4() with each of the four possible combinations of
SOCK_CLOEXEC and SOCK_NONBLOCK set/clear in 'flags', and verifies
that the appropriate flags are set on the file descriptor/open file
description returned by accept4().

I tested Ulrich's patch in this thread by applying against 2.6.28-rc2,
and it passes according to my test program.

/* test_accept4.c

  Copyright (C) 2008, Linux Foundation, written by Michael Kerrisk
       <mtk.manpages@gmail.com>

  Licensed under the GNU GPLv2 or later.
*/
#define _GNU_SOURCE
#include <unistd.h>
#include <sys/syscall.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <stdlib.h>
#include <fcntl.h>
#include <stdio.h>
#include <string.h>

#define PORT_NUM 33333

#define die(msg) do { perror(msg); exit(EXIT_FAILURE); } while (0)

/**********************************************************************/

/* The following is what we need until glibc gets a wrapper for
  accept4() */

/* Flags for socket(), socketpair(), accept4() */
#ifndef SOCK_CLOEXEC
#define SOCK_CLOEXEC    O_CLOEXEC
#endif
#ifndef SOCK_NONBLOCK
#define SOCK_NONBLOCK   O_NONBLOCK
#endif

#ifdef __x86_64__
#define SYS_accept4 288
#elif __i386__
#define USE_SOCKETCALL 1
#define SYS_ACCEPT4 18
#else
#error "Sorry -- don't know the syscall # on this architecture"
#endif

static int
accept4(int fd, struct sockaddr *sockaddr, socklen_t *addrlen, int flags)
{
   printf("Calling accept4(): flags = %x", flags);
   if (flags != 0) {
       printf(" (");
       if (flags & SOCK_CLOEXEC)
           printf("SOCK_CLOEXEC");
       if ((flags & SOCK_CLOEXEC) && (flags & SOCK_NONBLOCK))
           printf(" ");
       if (flags & SOCK_NONBLOCK)
           printf("SOCK_NONBLOCK");
       printf(")");
   }
   printf("\n");

#if USE_SOCKETCALL
   long args[6];

   args[0] = fd;
   args[1] = (long) sockaddr;
   args[2] = (long) addrlen;
   args[3] = flags;

   return syscall(SYS_socketcall, SYS_ACCEPT4, args);
#else
   return syscall(SYS_accept4, fd, sockaddr, addrlen, flags);
#endif
}

/**********************************************************************/

static int
do_test(int lfd, struct sockaddr_in *conn_addr,
       int closeonexec_flag, int nonblock_flag)
{
   int connfd, acceptfd;
   int fdf, flf, fdf_pass, flf_pass;
   struct sockaddr_in claddr;
   socklen_t addrlen;

   printf("=======================================\n");

   connfd = socket(AF_INET, SOCK_STREAM, 0);
   if (connfd == -1)
       die("socket");
   if (connect(connfd, (struct sockaddr *) conn_addr,
               sizeof(struct sockaddr_in)) == -1)
       die("connect");

   addrlen = sizeof(struct sockaddr_in);
   acceptfd = accept4(lfd, (struct sockaddr *) &claddr, &addrlen,
                      closeonexec_flag | nonblock_flag);
   if (acceptfd == -1) {
       perror("accept4()");
       close(connfd);
       return 0;
   }

   fdf = fcntl(acceptfd, F_GETFD);
   if (fdf == -1)
       die("fcntl:F_GETFD");
   fdf_pass = ((fdf & FD_CLOEXEC) != 0) ==
              ((closeonexec_flag & SOCK_CLOEXEC) != 0);
   printf("Close-on-exec flag is %sset (%s); ",
           (fdf & FD_CLOEXEC) ? "" : "not ",
           fdf_pass ? "OK" : "failed");

   flf = fcntl(acceptfd, F_GETFL);
   if (flf == -1)
       die("fcntl:F_GETFD");
   flf_pass = ((flf & O_NONBLOCK) != 0) ==
              ((nonblock_flag & SOCK_NONBLOCK) !=0);
   printf("nonblock flag is %sset (%s)\n",
           (flf & O_NONBLOCK) ? "" : "not ",
           flf_pass ? "OK" : "failed");

   close(acceptfd);
   close(connfd);

   printf("Test result: %s\n", (fdf_pass && flf_pass) ? "PASS" : "FAIL");
   return fdf_pass && flf_pass;
}

static int
create_listening_socket(int port_num)
{
   struct sockaddr_in svaddr;
   int lfd;
   int optval;

   memset(&svaddr, 0, sizeof(struct sockaddr_in));
   svaddr.sin_family = AF_INET;
   svaddr.sin_addr.s_addr = htonl(INADDR_ANY);
   svaddr.sin_port = htons(port_num);

   lfd = socket(AF_INET, SOCK_STREAM, 0);
   if (lfd == -1)
       die("socket");

   optval = 1;
   if (setsockopt(lfd, SOL_SOCKET, SO_REUSEADDR, &optval,
                  sizeof(optval)) == -1)
       die("setsockopt");

   if (bind(lfd, (struct sockaddr *) &svaddr,
            sizeof(struct sockaddr_in)) == -1)
       die("bind");

   if (listen(lfd, 5) == -1)
       die("listen");

   return lfd;
}

int
main(int argc, char *argv[])
{
   struct sockaddr_in conn_addr;
   int lfd;
   int port_num;
   int passed;

   passed = 1;

   port_num = (argc > 1) ? atoi(argv[1]) : PORT_NUM;

   memset(&conn_addr, 0, sizeof(struct sockaddr_in));
   conn_addr.sin_family = AF_INET;
   conn_addr.sin_addr.s_addr = htonl(INADDR_LOOPBACK);
   conn_addr.sin_port = htons(port_num);

   lfd = create_listening_socket(port_num);

   if (!do_test(lfd, &conn_addr, 0, 0))
       passed = 0;
   if (!do_test(lfd, &conn_addr, SOCK_CLOEXEC, 0))
       passed = 0;
   if (!do_test(lfd, &conn_addr, 0, SOCK_NONBLOCK))
       passed = 0;
   if (!do_test(lfd, &conn_addr, SOCK_CLOEXEC, SOCK_NONBLOCK))
       passed = 0;

   close(lfd);

   exit(passed ? EXIT_SUCCESS : EXIT_FAILURE);
}

[mtk.manpages@gmail.com: rewrote changelog, updated test program]
Signed-off-by: Ulrich Drepper <drepper@redhat.com>
Tested-by: Michael Kerrisk <mtk.manpages@gmail.com>
Acked-by: Michael Kerrisk <mtk.manpages@gmail.com>
Cc: <linux-api@vger.kernel.org>
Cc: <linux-arch@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2008-11-19 18:49:57 -08:00
..
9p 9p: restrict RDMA usage 2008-11-12 23:33:57 -08:00
802 net/802/fc.c: Fix compilation warnings 2008-10-15 00:13:53 -07:00
8021q vlan: Fix typos in proc output string 2008-11-10 13:37:40 -08:00
appletalk net: Rationalise email address: Network Specific Parts 2008-10-13 19:01:08 -07:00
atm net/atm/lec.c: drop code after return 2008-09-22 19:24:45 -07:00
ax25 ax25: Quick fix for making sure unaccepted sockets get destroyed. 2008-10-06 12:53:50 -07:00
bluetooth Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net-2.6 2008-10-17 08:58:52 -07:00
bridge net: Fix disjunct computation of netdev features 2008-10-23 01:11:29 -07:00
can net: Remove CONFIG_KMOD from net/ (towards removing CONFIG_KMOD entirely) 2008-10-16 15:24:51 -07:00
core rtnetlink: propagate error from dev_change_flags in do_setlink() 2008-11-16 23:20:31 -08:00
dccp dccp: Port redirection support for DCCP 2008-10-19 23:36:47 -07:00
decnet Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net-2.6 2008-10-17 08:58:52 -07:00
dsa dsa: fix master interface allmulti/promisc handling 2008-11-10 21:53:12 -08:00
econet netns: Use net_eq() to compare net-namespaces for optimization. 2008-07-19 22:34:43 -07:00
ethernet dsa: add support for Trailer tagging format 2008-10-08 17:24:16 -07:00
ieee80211 net/ieee80211: adjust error handling 2008-08-22 16:29:49 -04:00
ipv4 net: shy netns_ok check 2008-11-12 23:23:51 -08:00
ipv6 ipv6: routing header fixes 2008-11-12 22:59:21 -08:00
ipx netns: Use net_eq() to compare net-namespaces for optimization. 2008-07-19 22:34:43 -07:00
irda Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net-2.6 2008-07-20 17:43:29 -07:00
iucv iucv: Fix mismerge again. 2008-09-30 03:03:35 -07:00
key af_key: mark policy as dead before destroying 2008-11-06 23:08:37 -08:00
lapb
llc netns: Use net_eq() to compare net-namespaces for optimization. 2008-07-19 22:34:43 -07:00
mac80211 mac80211: fix notify_mac function 2008-11-12 16:49:53 -05:00
netfilter netfilter: payload_len is be16, add size of struct rather than size of pointer 2008-11-10 16:46:06 -08:00
netlabel netlabel: Fix compilation warnings in net/netlabel/netlabel_addrlist.c 2008-10-30 10:44:48 -04:00
netlink net: Remove CONFIG_KMOD from net/ (towards removing CONFIG_KMOD entirely) 2008-10-16 15:24:51 -07:00
netrom netrom: Fix sock_orphan() use in nr_release 2008-10-06 12:54:57 -07:00
packet net: convert BUG_TRAP to generic WARN_ON 2008-07-25 21:43:18 -07:00
phonet Phonet: refuse to send bigger than MTU packets 2008-11-16 19:48:49 -08:00
rfkill Fix logic error in rfkill_check_duplicity 2008-11-06 16:37:09 -05:00
rose netdev: Handle ->addr_list_lock just like ->_xmit_lock for lockdep. 2008-07-22 14:16:42 -07:00
rxrpc net/rxrpc: Use an IS_ERR test rather than a NULL test 2008-08-13 02:40:48 -07:00
sched Merge branch 'timers/range-hrtimers' into v28-range-hrtimers-for-linus-v2 2008-10-22 09:48:06 +02:00
sctp sctp: Fix to handle SHUTDOWN in SHUTDOWN_RECEIVED state 2008-10-23 01:01:18 -07:00
sunrpc SUNRPC: Fix potential race in put_rpccred() 2008-10-28 15:21:42 -04:00
tipc tipc: Don't use structure names which easily globally conflict. 2008-09-02 23:38:32 -07:00
unix net: unix: fix inflight counting bug in garbage collector 2008-11-09 11:17:33 -08:00
wanrouter wanmain.c doesn't need syncppp.h 2008-07-23 23:00:36 +02:00
wireless wireless: fix regression caused by regulatory config option 2008-10-26 10:38:52 -07:00
x25 netns: Use net_eq() to compare net-namespaces for optimization. 2008-07-19 22:34:43 -07:00
xfrm xfrm: Fix xfrm_policy_gc_lock handling. 2008-11-03 19:11:29 -08:00
compat.c reintroduce accept4 2008-11-19 18:49:57 -08:00
Kconfig net: Distributed Switch Architecture protocol support 2008-10-08 17:15:19 -07:00
Makefile net: Distributed Switch Architecture protocol support 2008-10-08 17:15:19 -07:00
nonet.c
socket.c reintroduce accept4 2008-11-19 18:49:57 -08:00
sysctl_net.c missing bits of net-namespace / sysctl 2008-07-27 09:45:34 -07:00
TUNABLE