rfork(2): add RFSPAWN flag
When RFSPAWN is passed, rfork exhibits vfork(2) semantics but also resets signal handlers in the child during creation to avoid a point of corruption of parent state from the child. This flag will be used by posix_spawn(3) to handle potential signal issues. Reviewed by: jilles, kib Differential Revision: https://reviews.freebsd.org/D19058
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Notes:
svn2git
2020-12-20 02:59:44 +00:00
svn path=/head/; revision=352711
@ -5,7 +5,7 @@
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.\"
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.\" $FreeBSD$
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.\"
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.Dd July 12, 2011
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.Dd September 25, 2019
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.Dt RFORK 2
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.Os
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.Sh NAME
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@ -34,7 +34,9 @@ and open files.
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The
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.Fa flags
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argument
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is the logical OR of some subset of:
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is either
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.Dv RFSPAWN
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or the logical OR of some subset of:
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.Bl -tag -width ".Dv RFLINUXTHPN"
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.It Dv RFPROC
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If set a new process is created; otherwise changes affect the
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@ -105,6 +107,14 @@ open until either they are explicitly closed
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or all processes sharing the table exit.
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.Pp
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If
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.Dv RFSPAWN
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is passed,
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.Nm
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will use
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.Xr vfork 2
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semantics but reset all signal actions in the child to default.
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.Pp
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If
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.Dv RFPROC
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is set, the
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value returned in the parent process
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@ -170,10 +170,18 @@ sys_rfork(struct thread *td, struct rfork_args *uap)
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/* Don't allow kernel-only flags. */
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if ((uap->flags & RFKERNELONLY) != 0)
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return (EINVAL);
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/* RFSPAWN must not appear with others */
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if ((uap->flags & RFSPAWN) != 0 && uap->flags != RFSPAWN)
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return (EINVAL);
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AUDIT_ARG_FFLAGS(uap->flags);
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bzero(&fr, sizeof(fr));
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fr.fr_flags = uap->flags;
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if ((uap->flags & RFSPAWN) != 0) {
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fr.fr_flags = RFFDG | RFPROC | RFPPWAIT | RFMEM;
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fr.fr_flags2 = FR2_DROPSIG_CAUGHT;
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} else {
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fr.fr_flags = uap->flags;
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}
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fr.fr_pidp = &pid;
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error = fork1(td, &fr);
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if (error == 0) {
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@ -471,6 +479,11 @@ do_fork(struct thread *td, struct fork_req *fr, struct proc *p2, struct thread *
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} else {
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sigacts_copy(newsigacts, p1->p_sigacts);
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p2->p_sigacts = newsigacts;
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if ((fr->fr_flags2 & FR2_DROPSIG_CAUGHT) != 0) {
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mtx_lock(&p2->p_sigacts->ps_mtx);
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sig_drop_caught(p2);
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mtx_unlock(&p2->p_sigacts->ps_mtx);
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}
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}
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if (fr->fr_flags & RFTSIGZMB)
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@ -986,12 +986,7 @@ execsigs(struct proc *p)
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PROC_LOCK_ASSERT(p, MA_OWNED);
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ps = p->p_sigacts;
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mtx_lock(&ps->ps_mtx);
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while (SIGNOTEMPTY(ps->ps_sigcatch)) {
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sig = sig_ffs(&ps->ps_sigcatch);
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sigdflt(ps, sig);
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if ((sigprop(sig) & SIGPROP_IGNORE) != 0)
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sigqueue_delete_proc(p, sig);
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}
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sig_drop_caught(p);
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/*
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* As CloudABI processes cannot modify signal handlers, fully
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@ -3857,3 +3852,20 @@ sigacts_shared(struct sigacts *ps)
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return (ps->ps_refcnt > 1);
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}
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void
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sig_drop_caught(struct proc *p)
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{
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int sig;
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struct sigacts *ps;
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ps = p->p_sigacts;
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PROC_LOCK_ASSERT(p, MA_OWNED);
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mtx_assert(&ps->ps_mtx, MA_OWNED);
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while (SIGNOTEMPTY(ps->ps_sigcatch)) {
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sig = sig_ffs(&ps->ps_sigcatch);
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sigdflt(ps, sig);
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if ((sigprop(sig) & SIGPROP_IGNORE) != 0)
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sigqueue_delete_proc(p, sig);
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}
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}
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@ -1006,6 +1006,8 @@ struct fork_req {
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int *fr_pd_fd;
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int fr_pd_flags;
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struct filecaps *fr_pd_fcaps;
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int fr_flags2;
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#define FR2_DROPSIG_CAUGHT 0x00001 /* Drop caught non-DFL signals */
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};
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/*
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@ -381,6 +381,7 @@ void sigacts_copy(struct sigacts *dest, struct sigacts *src);
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void sigacts_free(struct sigacts *ps);
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struct sigacts *sigacts_hold(struct sigacts *ps);
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int sigacts_shared(struct sigacts *ps);
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void sig_drop_caught(struct proc *p);
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void sigexit(struct thread *td, int sig) __dead2;
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int sigev_findtd(struct proc *p, struct sigevent *sigev, struct thread **);
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int sig_ffs(sigset_t *set);
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@ -188,11 +188,14 @@
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#define RFTSIGNUM(flags) (((flags) >> RFTSIGSHIFT) & RFTSIGMASK)
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#define RFTSIGFLAGS(signum) ((signum) << RFTSIGSHIFT)
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#define RFPROCDESC (1<<28) /* return a process descriptor */
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#define RFPPWAIT (1<<31) /* parent sleeps until child exits (vfork) */
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/* kernel: parent sleeps until child exits (vfork) */
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#define RFPPWAIT (1<<31)
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/* user: vfork(2) semantics, clear signals */
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#define RFSPAWN (1U<<31)
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#define RFFLAGS (RFFDG | RFPROC | RFMEM | RFNOWAIT | RFCFDG | \
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RFTHREAD | RFSIGSHARE | RFLINUXTHPN | RFSTOPPED | RFHIGHPID | RFTSIGZMB | \
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RFPROCDESC | RFPPWAIT)
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#define RFKERNELONLY (RFSTOPPED | RFHIGHPID | RFPPWAIT | RFPROCDESC)
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RFPROCDESC | RFSPAWN | RFPPWAIT)
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#define RFKERNELONLY (RFSTOPPED | RFHIGHPID | RFPROCDESC)
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#endif /* __BSD_VISIBLE */
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