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Revert "fork: fix use-after-free with vfork"

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This unreliably breaks libc handling of vfork where forking succeded,
but execve did not.

vfork code in libc performs waitpid with WNOHANG in case of failed exec.
With the fix exit codepath was waking up the parent before the child
fully transitioned to a zombie. Woken up parent would waitpid, which
could find a not-yet-zombie child and fail to reap it due to the WNOHANG
flag.

While removing the flag fixes the problem, it is not an option due to older
releases which would still suffer from the kernel change.

Revert the fix until a solution can be worked out.

Note that while use-after-free which gets back due to the revert is a real
bug, it's side-effects are limited due to the fact that struct proc memory
is never released by UMA.
This commit is contained in:
Mateusz Guzik 2018-11-23 04:38:50 +00:00
parent e9e747efe2
commit e3d3e8289b
3 changed files with 6 additions and 12 deletions
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16
sys/kern/kern_exit.c
View File

@ -284,15 +284,6 @@ exit1(struct thread *td, int rval, int signo)
p->p_flag |= P_WEXIT;
wakeup(&p->p_stype);
/*
* If P_PPWAIT is set our parent holds us with p_lock and may
* be waiting on p_pwait.
*/
if (p->p_flag & P_PPWAIT) {
p->p_flag &= ~P_PPWAIT;
cv_broadcast(&p->p_pwait);
}
/*
* Wait for any processes that have a hold on our vmspace to
* release their reference.
@ -338,9 +329,13 @@ exit1(struct thread *td, int rval, int signo)
*/
EVENTHANDLER_DIRECT_INVOKE(process_exit, p);
/*
* If parent is waiting for us to exit or exec,
* P_PPWAIT is set; we will wakeup the parent below.
*/
PROC_LOCK(p);
stopprofclock(p);
p->p_flag &= ~(P_TRACED | P_PPTRACE);
p->p_flag &= ~(P_TRACED | P_PPWAIT | P_PPTRACE);
p->p_ptevents = 0;
/*
@ -641,6 +636,7 @@ exit1(struct thread *td, int rval, int signo)
* proc lock.
*/
wakeup(p->p_pptr);
cv_broadcast(&p->p_pwait);
sched_exit(p->p_pptr, td);
PROC_SLOCK(p);
p->p_state = PRS_ZOMBIE;

1
sys/kern/kern_fork.c
View File

@ -720,7 +720,6 @@ do_fork(struct thread *td, struct fork_req *fr, struct proc *p2, struct thread *
dtrace_fasttrap_fork(p1, p2);
#endif
if (fr->fr_flags & RFPPWAIT) {
_PHOLD(p2);
td->td_pflags |= TDP_RFPPWAIT;
td->td_rfppwait_p = p2;
td->td_dbgflags |= TDB_VFORK;

1
sys/kern/subr_syscall.c
View File

@ -257,7 +257,6 @@ syscallret(struct thread *td, int error)
}
cv_timedwait(&p2->p_pwait, &p2->p_mtx, hz);
}
_PRELE(p2);
PROC_UNLOCK(p2);
if (td->td_dbgflags & TDB_VFORK) {