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Add accept4() system call.

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The accept4() function, compared to accept(), allows setting the new file
descriptor atomically close-on-exec and explicitly controlling the
non-blocking status on the new socket. (Note that the latter point means
that accept() is not equivalent to any form of accept4().)

The linuxulator's accept4 implementation leaves a race window where the new
file descriptor is not close-on-exec because it calls sys_accept(). This
implementation leaves no such race window (by using falloc() flags). The
linuxulator could be fixed and simplified by using the new code.

Like accept(), accept4() is async-signal-safe, a cancellation point and
permitted in capability mode.
This commit is contained in:
Jilles Tjoelker 2013-05-01 20:10:21 +00:00
parent 14f525595c
commit da7d2afb6d
11 changed files with 143 additions and 28 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

1
lib/libc/sys/Makefile.inc
View File

@ -270,6 +270,7 @@ MAN+= sctp_generic_recvmsg.2 \
wait.2 \
write.2
MLINKS+=accept.2 accept4.2
MLINKS+=access.2 eaccess.2 \
access.2 faccessat.2
MLINKS+=brk.2 sbrk.2

3
lib/libc/sys/Symbol.map
View File

@ -378,6 +378,7 @@ FBSD_1.2 {
};
FBSD_1.3 {
accept4;
bindat;
cap_fcntls_get;
cap_fcntls_limit;
@ -461,6 +462,8 @@ FBSDprivate_1.0 {
__sys_abort2;
_accept;
__sys_accept;
_accept4;
__sys_accept4;
_access;
__sys_access;
_acct;

45
lib/libc/sys/accept.2
View File

@ -41,6 +41,8 @@
.In sys/socket.h
.Ft int
.Fn accept "int s" "struct sockaddr * restrict addr" "socklen_t * restrict addrlen"
.Ft int
.Fn accept4 "int s" "struct sockaddr * restrict addr" "socklen_t * restrict addrlen" "int flags"
.Sh DESCRIPTION
The argument
.Fa s
@ -66,6 +68,26 @@ and
signals from the original socket
.Fa s .
.Pp
The
.Fn accept4
system call is similar,
but the
.Dv O_NONBLOCK
property of the new socket is instead determined by the
.Dv SOCK_NONBLOCK
flag in the
.Fa flags
argument,
the
.Dv O_ASYNC
property is cleared,
the signal destination is cleared
and the close-on-exec flag on the new file descriptor can be set via the
.Dv SOCK_CLOEXEC
flag in the
.Fa flags
argument.
.Pp
If no pending connections are
present on the queue, and the original socket
is not marked as non-blocking,
@ -141,13 +163,15 @@ properties and the signal destination being inherited,
but should set them explicitly using
.Xr fcntl 2 .
.Sh RETURN VALUES
The call returns \-1 on error.
If it succeeds, it returns a non-negative
These calls return \-1 on error.
If they succeed, they return a non-negative
integer that is a descriptor for the accepted socket.
.Sh ERRORS
The
.Fn accept
system call will fail if:
and
.Fn accept4
system calls will fail if:
.Bl -tag -width Er
.It Bq Er EBADF
The descriptor is invalid.
@ -176,6 +200,16 @@ are present to be accepted.
A connection arrived, but it was closed while waiting
on the listen queue.
.El
.Pp
The
.Fn accept4
system call will also fail if:
.Bl -tag -width Er
.It Bq Er EINVAL
The
.Fa flags
argument is invalid.
.El
.Sh SEE ALSO
.Xr bind 2 ,
.Xr connect 2 ,
@ -190,3 +224,8 @@ The
.Fn accept
system call appeared in
.Bx 4.2 .
.Pp
The
.Fn accept4
system call appeared in
.Fx 10.0 .

5
lib/libthr/pthread.map
View File

@ -181,6 +181,7 @@ FBSDprivate_1.0 {
___wait;
___waitpid;
__accept;
__accept4;
__aio_suspend;
__close;
__connect;
@ -408,3 +409,7 @@ FBSD_1.2 {
setcontext;
swapcontext;
};
FBSD_1.3 {
accept4;
};

22
lib/libthr/thread/thr_syscalls.c
View File

@ -101,6 +101,7 @@ extern pid_t __waitpid(pid_t, int *, int);
extern int __sys_aio_suspend(const struct aiocb * const[], int,
const struct timespec *);
extern int __sys_accept(int, struct sockaddr *, socklen_t *);
extern int __sys_accept4(int, struct sockaddr *, socklen_t *, int);
extern int __sys_connect(int, const struct sockaddr *, socklen_t);
extern int __sys_fsync(int);
extern int __sys_msync(void *, size_t, int);
@ -129,6 +130,7 @@ int ___usleep(useconds_t useconds);
pid_t ___wait(int *);
pid_t ___waitpid(pid_t, int *, int);
int __accept(int, struct sockaddr *, socklen_t *);
int __accept4(int, struct sockaddr *, socklen_t *, int);
int __aio_suspend(const struct aiocb * const iocbs[], int,
const struct timespec *);
int __close(int);
@ -176,6 +178,26 @@ __accept(int s, struct sockaddr *addr, socklen_t *addrlen)
return (ret);
}
__weak_reference(__accept4, accept4);
/*
* Cancellation behavior:
* If thread is canceled, no socket is created.
*/
int
__accept4(int s, struct sockaddr *addr, socklen_t *addrlen, int flags)
{
struct pthread *curthread;
int ret;
curthread = _get_curthread();
_thr_cancel_enter(curthread);
ret = __sys_accept4(s, addr, addrlen, flags);
_thr_cancel_leave(curthread, ret == -1);
return (ret);
}
__weak_reference(__aio_suspend, aio_suspend);
int

4
sys/compat/freebsd32/syscalls.master
View File

@ -1022,3 +1022,7 @@
int namelen); }
540 AUE_CHFLAGSAT NOPROTO { int chflagsat(int fd, const char *path, \
u_long flags, int atflag); }
541 AUE_ACCEPT NOPROTO { int accept4(int s, \
struct sockaddr * __restrict name, \
__socklen_t * __restrict anamelen, \
int flags); }

1
sys/kern/capabilities.conf
View File

@ -78,6 +78,7 @@ abort2
## relies on existing bindings on a socket, subject to capability rights.
##
accept
accept4
##
## Allow AIO operations by file descriptor, subject to capability rights.

4
sys/kern/syscalls.master
View File

@ -972,5 +972,9 @@
int namelen); }
540 AUE_CHFLAGSAT STD { int chflagsat(int fd, const char *path, \
u_long flags, int atflag); }
541 AUE_ACCEPT STD { int accept4(int s, \
struct sockaddr * __restrict name, \
__socklen_t * __restrict anamelen, \
int flags); }
; Please copy any additions and changes to the following compatability tables:
; sys/compat/freebsd32/syscalls.master

83
sys/kern/uipc_syscalls.c
View File

@ -97,10 +97,18 @@ __FBSDID("$FreeBSD$");
#endif /* SCTP */
#endif /* INET || INET6 */
/*
* Flags for accept1() and kern_accept4(), in addition to SOCK_CLOEXEC
* and SOCK_NONBLOCK.
*/
#define ACCEPT4_INHERIT 0x1
#define ACCEPT4_COMPAT 0x2
static int sendit(struct thread *td, int s, struct msghdr *mp, int flags);
static int recvit(struct thread *td, int s, struct msghdr *mp, void *namelenp);
static int accept1(struct thread *td, struct accept_args *uap, int compat);
static int accept1(struct thread *td, int s, struct sockaddr *uname,
socklen_t *anamelen, int flags);
static int do_sendfile(struct thread *td, struct sendfile_args *uap, int compat);
static int getsockname1(struct thread *td, struct getsockname_args *uap,
int compat);
@ -317,49 +325,46 @@ sys_listen(td, uap)
* accept1()
*/
static int
accept1(td, uap, compat)
accept1(td, s, uname, anamelen, flags)
struct thread *td;
struct accept_args /* {
int s;
struct sockaddr * __restrict name;
socklen_t * __restrict anamelen;
} */ *uap;
int compat;
int s;
struct sockaddr *uname;
socklen_t *anamelen;
int flags;
{
struct sockaddr *name;
socklen_t namelen;
struct file *fp;
int error;
if (uap->name == NULL)
return (kern_accept(td, uap->s, NULL, NULL, NULL));
if (uname == NULL)
return (kern_accept4(td, s, NULL, NULL, flags, NULL));
error = copyin(uap->anamelen, &namelen, sizeof (namelen));
error = copyin(anamelen, &namelen, sizeof (namelen));
if (error)
return (error);
error = kern_accept(td, uap->s, &name, &namelen, &fp);
error = kern_accept4(td, s, &name, &namelen, flags, &fp);
/*
* return a namelen of zero for older code which might
* ignore the return value from accept.
*/
if (error) {
(void) copyout(&namelen,
uap->anamelen, sizeof(*uap->anamelen));
(void) copyout(&namelen, anamelen, sizeof(*anamelen));
return (error);
}
if (error == 0 && name != NULL) {
if (error == 0 && uname != NULL) {
#ifdef COMPAT_OLDSOCK
if (compat)
if (flags & ACCEPT4_COMPAT)
((struct osockaddr *)name)->sa_family =
name->sa_family;
#endif
error = copyout(name, uap->name, namelen);
error = copyout(name, uname, namelen);
}
if (error == 0)
error = copyout(&namelen, uap->anamelen,
error = copyout(&namelen, anamelen,
sizeof(namelen));
if (error)
fdclose(td->td_proc->p_fd, fp, td->td_retval[0], td);
@ -371,6 +376,13 @@ accept1(td, uap, compat)
int
kern_accept(struct thread *td, int s, struct sockaddr **name,
socklen_t *namelen, struct file **fp)
{
return (kern_accept4(td, s, name, namelen, ACCEPT4_INHERIT, fp));
}
int
kern_accept4(struct thread *td, int s, struct sockaddr **name,
socklen_t *namelen, int flags, struct file **fp)
{
struct filedesc *fdp;
struct file *headfp, *nfp = NULL;
@ -400,7 +412,7 @@ kern_accept(struct thread *td, int s, struct sockaddr **name,
if (error != 0)
goto done;
#endif
error = falloc(td, &nfp, &fd, 0);
error = falloc(td, &nfp, &fd, (flags & SOCK_CLOEXEC) ? O_CLOEXEC : 0);
if (error)
goto done;
ACCEPT_LOCK();
@ -441,7 +453,10 @@ kern_accept(struct thread *td, int s, struct sockaddr **name,
TAILQ_REMOVE(&head->so_comp, so, so_list);
head->so_qlen--;
so->so_state |= (head->so_state & SS_NBIO);
if (flags & ACCEPT4_INHERIT)
so->so_state |= (head->so_state & SS_NBIO);
else
so->so_state |= (flags & SOCK_NONBLOCK) ? SS_NBIO : 0;
so->so_qstate &= ~SQ_COMP;
so->so_head = NULL;
@ -454,9 +469,15 @@ kern_accept(struct thread *td, int s, struct sockaddr **name,
/* connection has been removed from the listen queue */
KNOTE_UNLOCKED(&head->so_rcv.sb_sel.si_note, 0);
pgid = fgetown(&head->so_sigio);
if (pgid != 0)
fsetown(pgid, &so->so_sigio);
if (flags & ACCEPT4_INHERIT) {
pgid = fgetown(&head->so_sigio);
if (pgid != 0)
fsetown(pgid, &so->so_sigio);
} else {
fflag &= ~(FNONBLOCK | FASYNC);
if (flags & SOCK_NONBLOCK)
fflag |= FNONBLOCK;
}
finit(nfp, fflag, DTYPE_SOCKET, so, &socketops);
/* Sync socket nonblocking/async state with file flags */
@ -527,7 +548,18 @@ sys_accept(td, uap)
struct accept_args *uap;
{
return (accept1(td, uap, 0));
return (accept1(td, uap->s, uap->name, uap->anamelen, ACCEPT4_INHERIT));
}
int
sys_accept4(td, uap)
struct thread *td;
struct accept4_args *uap;
{
if (uap->flags & ~(SOCK_CLOEXEC | SOCK_NONBLOCK))
return (EINVAL);
return (accept1(td, uap->s, uap->name, uap->anamelen, uap->flags));
}
#ifdef COMPAT_OLDSOCK
@ -537,7 +569,8 @@ oaccept(td, uap)
struct accept_args *uap;
{
return (accept1(td, uap, 1));
return (accept1(td, uap->s, uap->name, uap->anamelen,
ACCEPT4_INHERIT | ACCEPT4_COMPAT));
}
#endif /* COMPAT_OLDSOCK */

1
sys/sys/socket.h
View File

@ -634,6 +634,7 @@ int accept(int, struct sockaddr * __restrict, socklen_t * __restrict);
int bind(int, const struct sockaddr *, socklen_t);
int connect(int, const struct sockaddr *, socklen_t);
#if __BSD_VISIBLE
int accept4(int, struct sockaddr * __restrict, socklen_t * __restrict, int);
int bindat(int, int, const struct sockaddr *, socklen_t);
int connectat(int, int, const struct sockaddr *, socklen_t);
#endif

2
sys/sys/syscallsubr.h
View File

@ -60,6 +60,8 @@ int kern___getcwd(struct thread *td, u_char *buf, enum uio_seg bufseg,
u_int buflen);
int kern_accept(struct thread *td, int s, struct sockaddr **name,
socklen_t *namelen, struct file **fp);
int kern_accept4(struct thread *td, int s, struct sockaddr **name,
socklen_t *namelen, int flags, struct file **fp);
int kern_access(struct thread *td, char *path, enum uio_seg pathseg,
int flags);
int kern_accessat(struct thread *td, int fd, char *path,