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reintroduce accept4

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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>
This commit is contained in:
Ulrich Drepper 2008-11-19 15:36:14 -08:00 committed by Linus Torvalds
parent cf7ee554f3
commit de11defebf
6 changed files with 21 additions and 124 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

4
arch/x86/include/asm/unistd_64.h
View File

@ -639,8 +639,8 @@ __SYSCALL(__NR_fallocate, sys_fallocate)
__SYSCALL(__NR_timerfd_settime, sys_timerfd_settime)
#define __NR_timerfd_gettime 287
__SYSCALL(__NR_timerfd_gettime, sys_timerfd_gettime)
#define __NR_paccept 288
__SYSCALL(__NR_paccept, sys_paccept)
#define __NR_accept4 288
__SYSCALL(__NR_accept4, sys_accept4)
#define __NR_signalfd4 289
__SYSCALL(__NR_signalfd4, sys_signalfd4)
#define __NR_eventfd2 290

6
include/linux/net.h
View File

@ -40,7 +40,7 @@
#define SYS_GETSOCKOPT 15 /* sys_getsockopt(2) */
#define SYS_SENDMSG 16 /* sys_sendmsg(2) */
#define SYS_RECVMSG 17 /* sys_recvmsg(2) */
#define SYS_PACCEPT 18 /* sys_paccept(2) */
#define SYS_ACCEPT4 18 /* sys_accept4(2) */
typedef enum {
SS_FREE = 0, /* not allocated */
@ -100,7 +100,7 @@ enum sock_type {
* remaining bits are used as flags. */
#define SOCK_TYPE_MASK 0xf
/* Flags for socket, socketpair, paccept */
/* Flags for socket, socketpair, accept4 */
#define SOCK_CLOEXEC O_CLOEXEC
#ifndef SOCK_NONBLOCK
#define SOCK_NONBLOCK O_NONBLOCK
@ -223,8 +223,6 @@ extern int sock_map_fd(struct socket *sock, int flags);
extern struct socket *sockfd_lookup(int fd, int *err);
#define sockfd_put(sock) fput(sock->file)
extern int net_ratelimit(void);
extern long do_accept(int fd, struct sockaddr __user *upeer_sockaddr,
int __user *upeer_addrlen, int flags);
#define net_random() random32()
#define net_srandom(seed) srandom32((__force u32)seed)

3
include/linux/syscalls.h
View File

@ -410,8 +410,7 @@ asmlinkage long sys_getsockopt(int fd, int level, int optname,
asmlinkage long sys_bind(int, struct sockaddr __user *, int);
asmlinkage long sys_connect(int, struct sockaddr __user *, int);
asmlinkage long sys_accept(int, struct sockaddr __user *, int __user *);
asmlinkage long sys_paccept(int, struct sockaddr __user *, int __user *,
const __user sigset_t *, size_t, int);
asmlinkage long sys_accept4(int, struct sockaddr __user *, int __user *, int);
asmlinkage long sys_getsockname(int, struct sockaddr __user *, int __user *);
asmlinkage long sys_getpeername(int, struct sockaddr __user *, int __user *);
asmlinkage long sys_send(int, void __user *, size_t, unsigned);

2
kernel/sys_ni.c
View File

@ -31,7 +31,7 @@ cond_syscall(sys_socketpair);
cond_syscall(sys_bind);
cond_syscall(sys_listen);
cond_syscall(sys_accept);
cond_syscall(sys_paccept);
cond_syscall(sys_accept4);
cond_syscall(sys_connect);
cond_syscall(sys_getsockname);
cond_syscall(sys_getpeername);

50
net/compat.c
View File

@ -725,7 +725,7 @@ EXPORT_SYMBOL(compat_mc_getsockopt);
static unsigned char nas[19]={AL(0),AL(3),AL(3),AL(3),AL(2),AL(3),
AL(3),AL(3),AL(4),AL(4),AL(4),AL(6),
AL(6),AL(2),AL(5),AL(5),AL(3),AL(3),
AL(6)};
AL(4)};
#undef AL
asmlinkage long compat_sys_sendmsg(int fd, struct compat_msghdr __user *msg, unsigned flags)
@ -738,52 +738,13 @@ asmlinkage long compat_sys_recvmsg(int fd, struct compat_msghdr __user *msg, uns
return sys_recvmsg(fd, (struct msghdr __user *)msg, flags | MSG_CMSG_COMPAT);
}
asmlinkage long compat_sys_paccept(int fd, struct sockaddr __user *upeer_sockaddr,
int __user *upeer_addrlen,
const compat_sigset_t __user *sigmask,
compat_size_t sigsetsize, int flags)
{
compat_sigset_t ss32;
sigset_t ksigmask, sigsaved;
int ret;
if (sigmask) {
if (sigsetsize != sizeof(compat_sigset_t))
return -EINVAL;
if (copy_from_user(&ss32, sigmask, sizeof(ss32)))
return -EFAULT;
sigset_from_compat(&ksigmask, &ss32);
sigdelsetmask(&ksigmask, sigmask(SIGKILL)|sigmask(SIGSTOP));
sigprocmask(SIG_SETMASK, &ksigmask, &sigsaved);
}
ret = do_accept(fd, upeer_sockaddr, upeer_addrlen, flags);
if (ret == -ERESTARTNOHAND) {
/*
* Don't restore the signal mask yet. Let do_signal() deliver
* the signal on the way back to userspace, before the signal
* mask is restored.
*/
if (sigmask) {
memcpy(&current->saved_sigmask, &sigsaved,
sizeof(sigsaved));
set_restore_sigmask();
}
} else if (sigmask)
sigprocmask(SIG_SETMASK, &sigsaved, NULL);
return ret;
}
asmlinkage long compat_sys_socketcall(int call, u32 __user *args)
{
int ret;
u32 a[6];
u32 a0, a1;
if (call < SYS_SOCKET || call > SYS_PACCEPT)
if (call < SYS_SOCKET || call > SYS_ACCEPT4)
return -EINVAL;
if (copy_from_user(a, args, nas[call]))
return -EFAULT;
@ -804,7 +765,7 @@ asmlinkage long compat_sys_socketcall(int call, u32 __user *args)
ret = sys_listen(a0, a1);
break;
case SYS_ACCEPT:
ret = do_accept(a0, compat_ptr(a1), compat_ptr(a[2]), 0);
ret = sys_accept4(a0, compat_ptr(a1), compat_ptr(a[2]), 0);
break;
case SYS_GETSOCKNAME:
ret = sys_getsockname(a0, compat_ptr(a1), compat_ptr(a[2]));
@ -844,9 +805,8 @@ asmlinkage long compat_sys_socketcall(int call, u32 __user *args)
case SYS_RECVMSG:
ret = compat_sys_recvmsg(a0, compat_ptr(a1), a[2]);
break;
case SYS_PACCEPT:
ret = compat_sys_paccept(a0, compat_ptr(a1), compat_ptr(a[2]),
compat_ptr(a[3]), a[4], a[5]);
case SYS_ACCEPT4:
ret = sys_accept4(a0, compat_ptr(a1), compat_ptr(a[2]), a[3]);
break;
default:
ret = -EINVAL;

80
net/socket.c
View File

@ -1426,8 +1426,8 @@ asmlinkage long sys_listen(int fd, int backlog)
* clean when we restucture accept also.
*/
long do_accept(int fd, struct sockaddr __user *upeer_sockaddr,
int __user *upeer_addrlen, int flags)
asmlinkage long sys_accept4(int fd, struct sockaddr __user *upeer_sockaddr,
int __user *upeer_addrlen, int flags)
{
struct socket *sock, *newsock;
struct file *newfile;
@ -1510,66 +1510,10 @@ long do_accept(int fd, struct sockaddr __user *upeer_sockaddr,
goto out_put;
}
#if 0
#ifdef HAVE_SET_RESTORE_SIGMASK
asmlinkage long sys_paccept(int fd, struct sockaddr __user *upeer_sockaddr,
int __user *upeer_addrlen,
const sigset_t __user *sigmask,
size_t sigsetsize, int flags)
{
sigset_t ksigmask, sigsaved;
int ret;
if (sigmask) {
/* XXX: Don't preclude handling different sized sigset_t's. */
if (sigsetsize != sizeof(sigset_t))
return -EINVAL;
if (copy_from_user(&ksigmask, sigmask, sizeof(ksigmask)))
return -EFAULT;
sigdelsetmask(&ksigmask, sigmask(SIGKILL)|sigmask(SIGSTOP));
sigprocmask(SIG_SETMASK, &ksigmask, &sigsaved);
}
ret = do_accept(fd, upeer_sockaddr, upeer_addrlen, flags);
if (ret < 0 && signal_pending(current)) {
/*
* Don't restore the signal mask yet. Let do_signal() deliver
* the signal on the way back to userspace, before the signal
* mask is restored.
*/
if (sigmask) {
memcpy(&current->saved_sigmask, &sigsaved,
sizeof(sigsaved));
set_restore_sigmask();
}
} else if (sigmask)
sigprocmask(SIG_SETMASK, &sigsaved, NULL);
return ret;
}
#else
asmlinkage long sys_paccept(int fd, struct sockaddr __user *upeer_sockaddr,
int __user *upeer_addrlen,
const sigset_t __user *sigmask,
size_t sigsetsize, int flags)
{
/* The platform does not support restoring the signal mask in the
* return path. So we do not allow using paccept() with a signal
* mask. */
if (sigmask)
return -EINVAL;
return do_accept(fd, upeer_sockaddr, upeer_addrlen, flags);
}
#endif
#endif
asmlinkage long sys_accept(int fd, struct sockaddr __user *upeer_sockaddr,
int __user *upeer_addrlen)
{
return do_accept(fd, upeer_sockaddr, upeer_addrlen, 0);
return sys_accept4(fd, upeer_sockaddr, upeer_addrlen, 0);
}
/*
@ -2096,7 +2040,7 @@ static const unsigned char nargs[19]={
AL(0),AL(3),AL(3),AL(3),AL(2),AL(3),
AL(3),AL(3),AL(4),AL(4),AL(4),AL(6),
AL(6),AL(2),AL(5),AL(5),AL(3),AL(3),
AL(6)
AL(4)
};
#undef AL
@ -2115,7 +2059,7 @@ asmlinkage long sys_socketcall(int call, unsigned long __user *args)
unsigned long a0, a1;
int err;
if (call < 1 || call > SYS_PACCEPT)
if (call < 1 || call > SYS_ACCEPT4)
return -EINVAL;
/* copy_from_user should be SMP safe. */
@ -2143,9 +2087,8 @@ asmlinkage long sys_socketcall(int call, unsigned long __user *args)
err = sys_listen(a0, a1);
break;
case SYS_ACCEPT:
err =
do_accept(a0, (struct sockaddr __user *)a1,
(int __user *)a[2], 0);
err = sys_accept4(a0, (struct sockaddr __user *)a1,
(int __user *)a[2], 0);
break;
case SYS_GETSOCKNAME:
err =
@ -2192,12 +2135,9 @@ asmlinkage long sys_socketcall(int call, unsigned long __user *args)
case SYS_RECVMSG:
err = sys_recvmsg(a0, (struct msghdr __user *)a1, a[2]);
break;
case SYS_PACCEPT:
err =
sys_paccept(a0, (struct sockaddr __user *)a1,
(int __user *)a[2],
(const sigset_t __user *) a[3],
a[4], a[5]);
case SYS_ACCEPT4:
err = sys_accept4(a0, (struct sockaddr __user *)a1,
(int __user *)a[2], a[3]);
break;
default:
err = -EINVAL;