freebsd-dev/sys/kern/subr_syscall.c
Mateusz Guzik b00b27e925 fork: fix use-after-free with vfork
The pointer to the child is stored without any reference held. Then it is
blindly used to wait until P_PPWAIT is cleared. However, if the child is
autoreaped it could have exited and get freed before the parent started
waiting.

Use the existing hold mechanism to mitigate the problem. Most common case
of doing exec remains unchanged. The corner case of doing exit performs
wake up before waiting for holds to clear.

Reviewed by:	kib
Sponsored by:	The FreeBSD Foundation
Differential Revision:	https://reviews.freebsd.org/D18295
2018-11-22 21:08:37 +00:00

272 lines
7.7 KiB
C

/*-
* SPDX-License-Identifier: BSD-4-Clause
*
* Copyright (C) 1994, David Greenman
* Copyright (c) 1990, 1993
* The Regents of the University of California. All rights reserved.
* Copyright (C) 2010 Konstantin Belousov <kib@freebsd.org>
*
* This code is derived from software contributed to Berkeley by
* the University of Utah, and William Jolitz.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
* 3. All advertising materials mentioning features or use of this software
* must display the following acknowledgement:
* This product includes software developed by the University of
* California, Berkeley and its contributors.
* 4. Neither the name of the University nor the names of its contributors
* may be used to endorse or promote products derived from this software
* without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS 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.
*
* from: @(#)trap.c 7.4 (Berkeley) 5/13/91
*/
#include "opt_capsicum.h"
#include "opt_ktrace.h"
__FBSDID("$FreeBSD$");
#include <sys/capsicum.h>
#include <sys/ktr.h>
#include <sys/vmmeter.h>
#ifdef KTRACE
#include <sys/uio.h>
#include <sys/ktrace.h>
#endif
#include <security/audit/audit.h>
static inline int
syscallenter(struct thread *td)
{
struct proc *p;
struct syscall_args *sa;
int error, traced;
VM_CNT_INC(v_syscall);
p = td->td_proc;
sa = &td->td_sa;
td->td_pticks = 0;
if (td->td_cowgen != p->p_cowgen)
thread_cow_update(td);
traced = (p->p_flag & P_TRACED) != 0;
if (traced || td->td_dbgflags & TDB_USERWR) {
PROC_LOCK(p);
td->td_dbgflags &= ~TDB_USERWR;
if (traced)
td->td_dbgflags |= TDB_SCE;
PROC_UNLOCK(p);
}
error = (p->p_sysent->sv_fetch_syscall_args)(td);
#ifdef KTRACE
if (KTRPOINT(td, KTR_SYSCALL))
ktrsyscall(sa->code, sa->narg, sa->args);
#endif
KTR_START4(KTR_SYSC, "syscall", syscallname(p, sa->code),
(uintptr_t)td, "pid:%d", td->td_proc->p_pid, "arg0:%p", sa->args[0],
"arg1:%p", sa->args[1], "arg2:%p", sa->args[2]);
if (error == 0) {
STOPEVENT(p, S_SCE, sa->narg);
if (p->p_flag & P_TRACED) {
PROC_LOCK(p);
if (p->p_ptevents & PTRACE_SCE)
ptracestop((td), SIGTRAP, NULL);
PROC_UNLOCK(p);
}
if (td->td_dbgflags & TDB_USERWR) {
/*
* Reread syscall number and arguments if
* debugger modified registers or memory.
*/
error = (p->p_sysent->sv_fetch_syscall_args)(td);
#ifdef KTRACE
if (KTRPOINT(td, KTR_SYSCALL))
ktrsyscall(sa->code, sa->narg, sa->args);
#endif
if (error != 0)
goto retval;
}
#ifdef CAPABILITY_MODE
/*
* In capability mode, we only allow access to system calls
* flagged with SYF_CAPENABLED.
*/
if (IN_CAPABILITY_MODE(td) &&
!(sa->callp->sy_flags & SYF_CAPENABLED)) {
error = ECAPMODE;
goto retval;
}
#endif
error = syscall_thread_enter(td, sa->callp);
if (error != 0)
goto retval;
#ifdef KDTRACE_HOOKS
/* Give the syscall:::entry DTrace probe a chance to fire. */
if (__predict_false(systrace_enabled &&
sa->callp->sy_entry != 0))
(*systrace_probe_func)(sa, SYSTRACE_ENTRY, 0);
#endif
AUDIT_SYSCALL_ENTER(sa->code, td);
error = (sa->callp->sy_call)(td, sa->args);
AUDIT_SYSCALL_EXIT(error, td);
/* Save the latest error return value. */
if ((td->td_pflags & TDP_NERRNO) == 0)
td->td_errno = error;
#ifdef KDTRACE_HOOKS
/* Give the syscall:::return DTrace probe a chance to fire. */
if (__predict_false(systrace_enabled &&
sa->callp->sy_return != 0))
(*systrace_probe_func)(sa, SYSTRACE_RETURN,
error ? -1 : td->td_retval[0]);
#endif
syscall_thread_exit(td, sa->callp);
}
retval:
KTR_STOP4(KTR_SYSC, "syscall", syscallname(p, sa->code),
(uintptr_t)td, "pid:%d", td->td_proc->p_pid, "error:%d", error,
"retval0:%#lx", td->td_retval[0], "retval1:%#lx",
td->td_retval[1]);
if (traced) {
PROC_LOCK(p);
td->td_dbgflags &= ~TDB_SCE;
PROC_UNLOCK(p);
}
(p->p_sysent->sv_set_syscall_retval)(td, error);
return (error);
}
static inline void
syscallret(struct thread *td, int error)
{
struct proc *p, *p2;
struct syscall_args *sa;
ksiginfo_t ksi;
int traced, error1;
KASSERT((td->td_pflags & TDP_FORKING) == 0,
("fork() did not clear TDP_FORKING upon completion"));
p = td->td_proc;
sa = &td->td_sa;
if ((trap_enotcap || (p->p_flag2 & P2_TRAPCAP) != 0) &&
IN_CAPABILITY_MODE(td)) {
error1 = (td->td_pflags & TDP_NERRNO) == 0 ? error :
td->td_errno;
if (error1 == ENOTCAPABLE || error1 == ECAPMODE) {
ksiginfo_init_trap(&ksi);
ksi.ksi_signo = SIGTRAP;
ksi.ksi_errno = error1;
ksi.ksi_code = TRAP_CAP;
trapsignal(td, &ksi);
}
}
/*
* Handle reschedule and other end-of-syscall issues
*/
userret(td, td->td_frame);
#ifdef KTRACE
if (KTRPOINT(td, KTR_SYSRET)) {
ktrsysret(sa->code, (td->td_pflags & TDP_NERRNO) == 0 ?
error : td->td_errno, td->td_retval[0]);
}
#endif
td->td_pflags &= ~TDP_NERRNO;
if (p->p_flag & P_TRACED) {
traced = 1;
PROC_LOCK(p);
td->td_dbgflags |= TDB_SCX;
PROC_UNLOCK(p);
} else
traced = 0;
/*
* This works because errno is findable through the
* register set. If we ever support an emulation where this
* is not the case, this code will need to be revisited.
*/
STOPEVENT(p, S_SCX, sa->code);
if (traced || (td->td_dbgflags & (TDB_EXEC | TDB_FORK)) != 0) {
PROC_LOCK(p);
/*
* If tracing the execed process, trap to the debugger
* so that breakpoints can be set before the program
* executes. If debugger requested tracing of syscall
* returns, do it now too.
*/
if (traced &&
((td->td_dbgflags & (TDB_FORK | TDB_EXEC)) != 0 ||
(p->p_ptevents & PTRACE_SCX) != 0))
ptracestop(td, SIGTRAP, NULL);
td->td_dbgflags &= ~(TDB_SCX | TDB_EXEC | TDB_FORK);
PROC_UNLOCK(p);
}
if (td->td_pflags & TDP_RFPPWAIT) {
/*
* Preserve synchronization semantics of vfork. If
* waiting for child to exec or exit, fork set
* P_PPWAIT on child, and there we sleep on our proc
* (in case of exit).
*
* Do it after the ptracestop() above is finished, to
* not block our debugger until child execs or exits
* to finish vfork wait.
*/
td->td_pflags &= ~TDP_RFPPWAIT;
p2 = td->td_rfppwait_p;
again:
PROC_LOCK(p2);
while (p2->p_flag & P_PPWAIT) {
PROC_LOCK(p);
if (thread_suspend_check_needed()) {
PROC_UNLOCK(p2);
thread_suspend_check(0);
PROC_UNLOCK(p);
goto again;
} else {
PROC_UNLOCK(p);
}
cv_timedwait(&p2->p_pwait, &p2->p_mtx, hz);
}
_PRELE(p2);
PROC_UNLOCK(p2);
if (td->td_dbgflags & TDB_VFORK) {
PROC_LOCK(p);
if (p->p_ptevents & PTRACE_VFORK)
ptracestop(td, SIGTRAP, NULL);
td->td_dbgflags &= ~TDB_VFORK;
PROC_UNLOCK(p);
}
}
}