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Current pselect(3) is implemented in usermode and thus vulnerable to

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well-known race condition, which elimination was the reason for the
function appearance in first place. If sigmask supplied as argument to
pselect() enables a signal, the signal might be delivered before thread
called select(2), causing lost wakeup. Reimplement pselect() in kernel,
making change of sigmask and sleep atomic.

Since signal shall be delivered to the usermode, but sigmask restored,
set TDP_OLDMASK and save old mask in td_oldsigmask. The TDP_OLDMASK
should be cleared by ast() in case signal was not gelivered during
syscall execution.

Reviewed by:	davidxu
Tested by:	pho
MFC after:	1 month
This commit is contained in:
Konstantin Belousov 2009-10-27 10:55:34 +00:00
parent d6e029adbe
commit 066d836b02
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=198508
9 changed files with 109 additions and 82 deletions
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78
lib/libc/gen/pselect.c
View File

@ -1,78 +0,0 @@
/*
* Copyright 2000 Massachusetts Institute of Technology
*
* Permission to use, copy, modify, and distribute this software and
* its documentation for any purpose and without fee is hereby
* granted, provided that both the above copyright notice and this
* permission notice appear in all copies, that both the above
* copyright notice and this permission notice appear in all
* supporting documentation, and that the name of M.I.T. not be used
* in advertising or publicity pertaining to distribution of the
* software without specific, written prior permission. M.I.T. makes
* no representations about the suitability of this software for any
* purpose. It is provided "as is" without express or implied
* warranty.
*
* THIS SOFTWARE IS PROVIDED BY M.I.T. ``AS IS''. M.I.T. DISCLAIMS
* ALL EXPRESS OR IMPLIED WARRANTIES WITH REGARD TO THIS SOFTWARE,
* INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
* MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. IN NO EVENT
* SHALL M.I.T. BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
* LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
* USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
* ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
* OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
* OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*/
#include <sys/cdefs.h>
__FBSDID("$FreeBSD$");
#include "namespace.h"
#include <sys/select.h>
#include <sys/time.h>
#include <errno.h>
#include <signal.h>
#include "un-namespace.h"
__weak_reference(__pselect, pselect);
/*
* Emulate the POSIX 1003.1g-2000 `pselect' interface. This is the
* same as the traditional BSD `select' function, except that it uses
* a timespec rather than a timeval, doesn't modify the timeout argument,
* and allows the user to specify a signal mask to apply during the select.
*/
int
__pselect(int count, fd_set * __restrict rfds, fd_set * __restrict wfds,
fd_set * __restrict efds, const struct timespec * __restrict timo,
const sigset_t * __restrict mask)
{
sigset_t omask;
struct timeval tvtimo, *tvp;
int rv, sverrno;
if (timo) {
TIMESPEC_TO_TIMEVAL(&tvtimo, timo);
tvp = &tvtimo;
} else
tvp = 0;
if (mask != 0) {
rv = _sigprocmask(SIG_SETMASK, mask, &omask);
if (rv != 0)
return rv;
}
rv = _select(count, rfds, wfds, efds, tvp);
if (mask != 0) {
sverrno = errno;
_sigprocmask(SIG_SETMASK, &omask, (sigset_t *)0);
errno = sverrno;
}
return rv;
}

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

@ -211,6 +211,7 @@ FBSD_1.0 {
posix_openpt;
preadv;
profil;
pselect;
ptrace;
pwritev;
quotactl;
@ -781,6 +782,8 @@ FBSDprivate_1.0 {
__sys_preadv;
_profil;
__sys_profil;
_pselect;
__sys_pselect;
_ptrace;
__sys_ptrace;
_pwritev;

4
lib/libthr/thread/thr_syscalls.c
View File

@ -104,6 +104,8 @@ extern int __sys_accept(int, struct sockaddr *, socklen_t *);
extern int __sys_connect(int, const struct sockaddr *, socklen_t);
extern int __sys_fsync(int);
extern int __sys_msync(void *, size_t, int);
extern int __sys_pselect(int, fd_set *, fd_set *, fd_set *,
const struct timespec *, const sigset_t *);
extern int __sys_poll(struct pollfd *, unsigned, int);
extern ssize_t __sys_recv(int, void *, size_t, int);
extern ssize_t __sys_recvfrom(int, void *, size_t, int, struct sockaddr *, socklen_t *);
@ -394,7 +396,7 @@ ___pselect(int count, fd_set *rfds, fd_set *wfds, fd_set *efds,
int ret;
_thr_cancel_enter(curthread);
ret = __pselect(count, rfds, wfds, efds, timo, mask);
ret = __sys_pselect(count, rfds, wfds, efds, timo, mask);
_thr_cancel_leave(curthread);
return (ret);

35
sys/compat/freebsd32/freebsd32_misc.c
View File

@ -593,6 +593,41 @@ freebsd32_select(struct thread *td, struct freebsd32_select_args *uap)
sizeof(int32_t) * 8));
}
int
freebsd32_pselect(struct thread *td, struct freebsd32_pselect_args *uap)
{
struct timespec32 ts32;
struct timespec ts;
struct timeval tv, *tvp;
sigset_t set, *uset;
int error;
if (uap->ts != NULL) {
error = copyin(uap->ts, &ts32, sizeof(ts32));
if (error != 0)
return (error);
CP(ts32, ts, tv_sec);
CP(ts32, ts, tv_nsec);
TIMESPEC_TO_TIMEVAL(&tv, &ts);
tvp = &tv;
} else
tvp = NULL;
if (uap->sm != NULL) {
error = copyin(uap->sm, &set, sizeof(set));
if (error != 0)
return (error);
uset = &set;
} else
uset = NULL;
/*
* XXX big-endian needs to convert the fd_sets too.
* XXX Do pointers need PTRIN()?
*/
error = kern_pselect(td, uap->nd, uap->in, uap->ou, uap->ex, tvp,
uset, sizeof(int32_t) * 8);
return (error);
}
/*
* Copy 'count' items into the destination list pointed to by uap->eventlist.
*/

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

@ -909,3 +909,7 @@
519 AUE_PDKILL UNIMPL pdkill
520 AUE_PDGETPID UNIMPL pdgetpid
521 AUE_PDWAIT UNIMPL pdwait
522 AUE_SELECT STD { int freebsd32_pselect(int nd, fd_set *in, \
fd_set *ou, fd_set *ex, \
const struct timespec32 *ts, \
const sigset_t *sm); }

5
sys/kern/subr_trap.c
View File

@ -245,6 +245,11 @@ ast(struct trapframe *framep)
PROC_UNLOCK(p);
}
if (td->td_pflags & TDP_OLDMASK) {
td->td_pflags &= ~TDP_OLDMASK;
kern_sigprocmask(td, SIG_SETMASK, &td->td_oldsigmask, NULL, 0);
}
userret(td, framep);
mtx_assert(&Giant, MA_NOTOWNED);
}

56
sys/kern/sys_generic.c
View File

@ -751,6 +751,58 @@ poll_no_poll(int events)
return (events & (POLLIN | POLLOUT | POLLRDNORM | POLLWRNORM));
}
int
pselect(struct thread *td, struct pselect_args *uap)
{
struct timespec ts;
struct timeval tv, *tvp;
sigset_t set, *uset;
int error;
if (uap->ts != NULL) {
error = copyin(uap->ts, &ts, sizeof(ts));
if (error != 0)
return (error);
TIMESPEC_TO_TIMEVAL(&tv, &ts);
tvp = &tv;
} else
tvp = NULL;
if (uap->sm != NULL) {
error = copyin(uap->sm, &set, sizeof(set));
if (error != 0)
return (error);
uset = &set;
} else
uset = NULL;
return (kern_pselect(td, uap->nd, uap->in, uap->ou, uap->ex, tvp,
uset, NFDBITS));
}
int
kern_pselect(struct thread *td, int nd, fd_set *in, fd_set *ou, fd_set *ex,
struct timeval *tvp, sigset_t *uset, int abi_nfdbits)
{
int error;
if (uset != NULL) {
error = kern_sigprocmask(td, SIG_SETMASK, uset,
&td->td_oldsigmask, 0);
if (error != 0)
return (error);
td->td_pflags |= TDP_OLDMASK;
/*
* Make sure that ast() is called on return to
* usermode and TDP_OLDMASK is cleared, restoring old
* sigmask.
*/
thread_lock(td);
td->td_flags |= TDF_ASTPENDING;
thread_unlock(td);
}
error = kern_select(td, nd, in, ou, ex, tvp, abi_nfdbits);
return (error);
}
#ifndef _SYS_SYSPROTO_H_
struct select_args {
int nd;
@ -759,9 +811,7 @@ struct select_args {
};
#endif
int
select(td, uap)
register struct thread *td;
register struct select_args *uap;
select(struct thread *td, struct select_args *uap)
{
struct timeval tv, *tvp;
int error;

4
sys/kern/syscalls.master
View File

@ -919,5 +919,9 @@
519 AUE_PDKILL UNIMPL pdkill
520 AUE_PDGETPID UNIMPL pdgetpid
521 AUE_PDWAIT UNIMPL pdwait
522 AUE_SELECT STD { int pselect(int nd, fd_set *in, \
fd_set *ou, fd_set *ex, \
const struct timespec *ts, \
const sigset_t *sm); }
; Please copy any additions and changes to the following compatability tables:
; sys/compat/freebsd32/syscalls.master

2
sys/sys/syscallsubr.h
View File

@ -148,6 +148,8 @@ int kern_pathconf(struct thread *td, char *path, enum uio_seg pathseg,
int name, u_long flags);
int kern_pipe(struct thread *td, int fildes[2]);
int kern_preadv(struct thread *td, int fd, struct uio *auio, off_t offset);
int kern_pselect(struct thread *td, int nd, fd_set *in, fd_set *ou,
fd_set *ex, struct timeval *tvp, sigset_t *uset, int abi_nfdbits);
int kern_ptrace(struct thread *td, int req, pid_t pid, void *addr,
int data);
int kern_pwritev(struct thread *td, int fd, struct uio *auio, off_t offset);