Subject: [PATCH 02/18] flag parameters: paccept

From: Ulrich Drepper <[email-masked]>
Date: Tue, 6 May 2008 17:18:07 -0400

This patch is by far the most complex in the series.  It adds a new syscall
paccept.  This syscall differs from accept in that it adds (at the userlevel)
two additional parameters:

- a signal mask
- a flags value

The flags parameter can be used to set flag like SOCK_CLOEXEC.  This is
imlpemented here as well.  Some people argued that this is a property
which should be inherited from the file desriptor for the server but
this is against POSIX.  Additionally, we really want the signal mask
parameter as well (similar to pselect, ppoll, etc).  So an interface
change in inevitable.

The flag value is the same as for socket and socketpair.  I think
diverging here will only create confusion.  Similar to the filesystem
interfaces where the use of the O_* constants differs, it is acceptable
here.

The signal mask is handled as for pselect etc.  The mask is temporarily
installed for the thread and removed before the call returns.  I modeled
the code after pselect.  If there is a problem it's likely also in
pselect.

For architectures which use socketcall I maintained this interface
instead of adding a system call.  The symmetry shouldn't be broken.

The following test must be adjusted for architectures other than x86 and
x86-64 and in case the syscall numbers changed.

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
#include <errno.h>
#include <fcntl.h>
#include <pthread.h>
#include <signal.h>
#include <stdio.h>
#include <unistd.h>
#include <netinet/in.h>
#include <sys/socket.h>
#include <sys/syscall.h>

#ifndef __NR_paccept
# ifdef __x86_64__
#  define __NR_paccept 288
# elif defined __i386__
#  define SYS_PACCEPT 18
#  define USE_SOCKETCALL 1
# else
#  error "need __NR_paccept"
# endif
#endif

#ifdef USE_SOCKETCALL
# define paccept(fd, addr, addrlen, mask, flags) \
  ({ long args[6] = { \
       (long) fd, (long) addr, (long) addrlen, (long) mask, 8, (long) flags }; \
     syscall (__NR_socketcall, SYS_PACCEPT, args); })
#else
# define paccept(fd, addr, addrlen, mask, flags) \
  syscall (__NR_paccept, fd, addr, addrlen, mask, 8, flags)
#endif

#define PORT 57392

#define SOCK_CLOEXEC O_CLOEXEC

static pthread_barrier_t b;

static void *
tf (void *arg)
{
  pthread_barrier_wait (&b);
  int s = socket (AF_INET, SOCK_STREAM, 0);
  struct sockaddr_in sin;
  sin.sin_family = AF_INET;
  sin.sin_addr.s_addr = htonl (INADDR_LOOPBACK);
  sin.sin_port = htons (PORT);
  connect (s, (const struct sockaddr *) &sin, sizeof (sin));
  close (s);

  pthread_barrier_wait (&b);
  s = socket (AF_INET, SOCK_STREAM, 0);
  sin.sin_port = htons (PORT);
  connect (s, (const struct sockaddr *) &sin, sizeof (sin));
  close (s);
  pthread_barrier_wait (&b);

  pthread_barrier_wait (&b);
  sleep (2);
  pthread_kill ((pthread_t) arg, SIGUSR1);
  
  return NULL;
}

static void
handler (int s)
{
}

int
main (void)
{
  pthread_barrier_init (&b, NULL, 2);

  struct sockaddr_in sin;
  pthread_t th;
  if (pthread_create (&th, NULL, tf, (void *) pthread_self ()) != 0)
    {
      puts ("pthread_create failed");
      return 1;
    }

  int s = socket (AF_INET, SOCK_STREAM, 0);
  int reuse = 1;
  setsockopt (s, SOL_SOCKET, SO_REUSEADDR, &reuse, sizeof (reuse));
  sin.sin_family = AF_INET;
  sin.sin_addr.s_addr = htonl (INADDR_LOOPBACK);
  sin.sin_port = htons (PORT);
  bind (s, (struct sockaddr *) &sin, sizeof (sin));
  listen (s, SOMAXCONN);

  pthread_barrier_wait (&b);

  int s2 = paccept (s, NULL, 0, NULL, 0);
  if (s2 < 0)
    {
      puts ("paccept(0) failed");
      return 1;
    }

  int coe = fcntl (s2, F_GETFD);
  if (coe & FD_CLOEXEC)
    {
      puts ("paccept(0) set close-on-exec-flag");
      return 1;
    }
  close (s2);

  pthread_barrier_wait (&b);

  s2 = paccept (s, NULL, 0, NULL, SOCK_CLOEXEC);
  if (s2 < 0)
    {
      puts ("paccept(SOCK_CLOEXEC) failed");
      return 1;
    }

  coe = fcntl (s2, F_GETFD);
  if ((coe & FD_CLOEXEC) == 0)
    {
      puts ("paccept(SOCK_CLOEXEC) does not set close-on-exec flag");
      return 1;
    }
  close (s2);

  pthread_barrier_wait (&b);

  struct sigaction sa;
  sa.sa_handler = handler;
  sa.sa_flags = 0;
  sigemptyset (&sa.sa_mask);
  sigaction (SIGUSR1, &sa, NULL);

  sigset_t ss;
  pthread_sigmask (SIG_SETMASK, NULL, &ss);
  sigaddset (&ss, SIGUSR1);
  pthread_sigmask (SIG_SETMASK, &ss, NULL);

  sigdelset (&ss, SIGUSR1);
  alarm (4);
  pthread_barrier_wait (&b);

  errno = 0 ;
  s2 = paccept (s, NULL, 0, &ss, 0);
  if (s2 != -1 || errno != EINTR)
    {
      puts ("paccept did not fail with EINTR");
      return 1;
    }

  close (s);

  puts ("OK");

  return 0;
}
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

 include/asm-x86/unistd_64.h |    2 +
 include/linux/net.h         |    3 +
 include/linux/syscalls.h    |    2 +
 net/compat.c                |   52 +++++++++++++++++++++++++++++---
 net/socket.c                |   71 +++++++++++++++++++++++++++++++++++++++-----
 5 files changed, 118 insertions(+), 12 deletions(-)

Signed-off-by: Ulrich Drepper <[email-masked]>

diff --git a/include/asm-x86/unistd_64.h b/include/asm-x86/unistd_64.h
index fe26e36..d751135 100644
--- a/include/asm-x86/unistd_64.h
+++ b/include/asm-x86/unistd_64.h
@@ -639,6 +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)

 #ifndef __NO_STUBS
diff --git a/include/linux/net.h b/include/linux/net.h
index 0c1ad01..b4ad432 100644
--- a/include/linux/net.h
+++ b/include/linux/net.h
@@ -47,6 +47,7 @@ struct net;
 #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)		*/
 
 typedef enum {
 	SS_FREE = 0,			/* not allocated		*/
@@ -219,6 +220,8 @@ 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)
diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
index 0522f36..e022405 100644
--- a/include/linux/syscalls.h
+++ b/include/linux/syscalls.h
@@ -409,6 +409,8 @@ 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 sigset_t *, size_t, 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);
diff --git a/net/compat.c b/net/compat.c
index c823f6f..c9a507c 100644
--- a/net/compat.c
+++ b/net/compat.c
@@ -722,9 +722,10 @@ EXPORT_SYMBOL(compat_mc_getsockopt);
 
 /* Argument list sizes for compat_sys_socketcall */
 #define AL(x) ((x) * sizeof(u32))
-static unsigned char nas[18]={AL(0),AL(3),AL(3),AL(3),AL(2),AL(3),
+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(2),AL(5),AL(5),AL(3),AL(3),
+				AL(6)};
 #undef AL
 
 asmlinkage long compat_sys_sendmsg(int fd, struct compat_msghdr __user *msg, unsigned flags)
@@ -737,13 +738,52 @@ 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_thread_flag(TIF_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_RECVMSG)
+	if (call < SYS_SOCKET || call > SYS_PACCEPT)
 		return -EINVAL;
 	if (copy_from_user(a, args, nas[call]))
 		return -EFAULT;
@@ -764,7 +804,7 @@ asmlinkage long compat_sys_socketcall(int call, u32 __user *args)
 		ret = sys_listen(a0, a1);
 		break;
 	case SYS_ACCEPT:
-		ret = sys_accept(a0, compat_ptr(a1), compat_ptr(a[2]));
+		ret = do_accept(a0, compat_ptr(a1), compat_ptr(a[2]), 0);
 		break;
 	case SYS_GETSOCKNAME:
 		ret = sys_getsockname(a0, compat_ptr(a1), compat_ptr(a[2]));
@@ -804,6 +844,10 @@ 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]);
+		break;
 	default:
 		ret = -EINVAL;
 		break;
diff --git a/net/socket.c b/net/socket.c
index 6d6f406..634ad83 100644
--- a/net/socket.c
+++ b/net/socket.c
@@ -1412,14 +1412,17 @@ asmlinkage long sys_listen(int fd, int backlog)
  *	clean when we restucture accept also.
  */
 
-asmlinkage long sys_accept(int fd, struct sockaddr __user *upeer_sockaddr,
-			   int __user *upeer_addrlen)
+long do_accept(int fd, struct sockaddr __user *upeer_sockaddr,
+	       int __user *upeer_addrlen, int flags)
 {
 	struct socket *sock, *newsock;
 	struct file *newfile;
 	int err, len, newfd, fput_needed;
 	char address[MAX_SOCK_ADDR];
 
+	if (flags & ~SOCK_CLOEXEC)
+		return -EINVAL;
+
 	sock = sockfd_lookup_light(fd, &err, &fput_needed);
 	if (!sock)
 		goto out;
@@ -1437,7 +1440,7 @@ asmlinkage long sys_accept(int fd, struct sockaddr __user *upeer_sockaddr,
 	 */
 	__module_get(newsock->ops->owner);
 
-	newfd = sock_alloc_fd(&newfile, 0);
+	newfd = sock_alloc_fd(&newfile, flags & O_CLOEXEC);
 	if (unlikely(newfd < 0)) {
 		err = newfd;
 		sock_release(newsock);
@@ -1490,6 +1493,50 @@ out_fd:
 	goto out_put;
 }
 
+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_thread_flag(TIF_RESTORE_SIGMASK);
+		}
+	} else if (sigmask)
+		sigprocmask(SIG_SETMASK, &sigsaved, NULL);
+
+	return ret;
+}
+
+asmlinkage long sys_accept(int fd, struct sockaddr __user *upeer_sockaddr,
+			   int __user *upeer_addrlen)
+{
+	return do_accept(fd, upeer_sockaddr, upeer_addrlen, 0);
+}
+
 /*
  *	Attempt to connect to a socket with the server address.  The address
  *	is in user space so we verify it is OK and move it to kernel space.
@@ -2000,10 +2047,11 @@ out:
 
 /* Argument list sizes for sys_socketcall */
 #define AL(x) ((x) * sizeof(unsigned long))
-static const unsigned char nargs[18]={
+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(2),AL(5),AL(5),AL(3),AL(3),
+	AL(6)
 };
 
 #undef AL
@@ -2022,7 +2070,7 @@ asmlinkage long sys_socketcall(int call, unsigned long __user *args)
 	unsigned long a0, a1;
 	int err;
 
-	if (call < 1 || call > SYS_RECVMSG)
+	if (call < 1 || call > SYS_PACCEPT)
 		return -EINVAL;
 
 	/* copy_from_user should be SMP safe. */
@@ -2051,8 +2099,8 @@ asmlinkage long sys_socketcall(int call, unsigned long __user *args)
 		break;
 	case SYS_ACCEPT:
 		err =
-		    sys_accept(a0, (struct sockaddr __user *)a1,
-			       (int __user *)a[2]);
+		    do_accept(a0, (struct sockaddr __user *)a1,
+			      (int __user *)a[2], 0);
 		break;
 	case SYS_GETSOCKNAME:
 		err =
@@ -2099,6 +2147,13 @@ 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]);
+		break;
 	default:
 		err = -EINVAL;
 		break;