Restore the sys_o58_kill system call.

By keeping both the new (sys_kill/sys_thrkill) and old (sys_o58_kill)
system calls for the OpenBSD 6.0 release, code that uses either of these
mechanisms will work on both of the supported OpenBSD releases. This
provides a clean transition for runtimes that make direct system calls
(namely the Go programming language).

This requires a minimal amount of non-intrusive code and does not block
development progress within OpenBSD.

ok deraadt@ guenther@

2 files changed, 60 insertions, 2 deletions

diff --git a/sys/kern/kern_pledge.c b/sys/kern/kern_pledge.c
index 1a3a9e51395..047225c0933 100644
--- a/sys/kern/kern_pledge.c
+++ b/sys/kern/kern_pledge.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: kern_pledge.c,v 1.171 2016/06/27 16:33:48 jca Exp $	*/
+/*	$OpenBSD: kern_pledge.c,v 1.172 2016/06/27 16:49:45 jsing Exp $	*/
 
 /*
  * Copyright (c) 2015 Nicholas Marriott <nicm@openbsd.org>
@@ -230,6 +230,7 @@ const uint64_t pledge_syscalls[SYS_MAXSYSCALL] = {
 	 * Can kill self with "stdio".  Killing another pid
 	 * requires "proc"
 	 */
+	[SYS_o58_kill] = PLEDGE_STDIO,
 	[SYS_kill] = PLEDGE_STDIO,
 
 	/*
diff --git a/sys/kern/kern_sig.c b/sys/kern/kern_sig.c
index 7b9cba2cf9a..db92fb2d715 100644
--- a/sys/kern/kern_sig.c
+++ b/sys/kern/kern_sig.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: kern_sig.c,v 1.198 2016/06/11 21:41:50 tedu Exp $	*/
+/*	$OpenBSD: kern_sig.c,v 1.199 2016/06/27 16:49:45 jsing Exp $	*/
 /*	$NetBSD: kern_sig.c,v 1.54 1996/04/22 01:38:32 christos Exp $	*/
 
 /*
@@ -560,6 +560,63 @@ sys_sigaltstack(struct proc *p, void *v, register_t *retval)
 }
 
 int
+sys_o58_kill(struct proc *cp, void *v, register_t *retval)
+{
+	struct sys_o58_kill_args /* {
+		syscallarg(int) pid;
+		syscallarg(int) signum;
+	} */ *uap = v;
+	struct proc *p;
+	int pid = SCARG(uap, pid);
+	int signum = SCARG(uap, signum);
+	int error;
+
+	if (pid <= THREAD_PID_OFFSET && (error = pledge_kill(cp, pid)) != 0)
+		return (error);
+	if (((u_int)signum) >= NSIG)
+		return (EINVAL);
+	if (pid > 0) {
+		enum signal_type type = SPROCESS;
+
+		/*
+		 * If the target pid is > THREAD_PID_OFFSET then this
+		 * must be a kill of another thread in the same process.
+		 * Otherwise, this is a process kill and the target must
+		 * be a main thread.
+		 */
+		if (pid > THREAD_PID_OFFSET) {
+			if ((p = pfind(pid - THREAD_PID_OFFSET)) == NULL)
+				return (ESRCH);
+			if (p->p_p != cp->p_p)
+				return (ESRCH);
+			type = STHREAD;
+		} else {
+			/* XXX use prfind() */
+			if ((p = pfind(pid)) == NULL)
+				return (ESRCH);
+			if (p->p_flag & P_THREAD)
+				return (ESRCH);
+			if (!cansignal(cp, p->p_p, signum))
+				return (EPERM);
+		}
+
+		/* kill single process or thread */
+		if (signum)
+			ptsignal(p, signum, type);
+		return (0);
+	}
+	switch (pid) {
+	case -1:		/* broadcast signal */
+		return (killpg1(cp, signum, 0, 1));
+	case 0:			/* signal own process group */
+		return (killpg1(cp, signum, 0, 0));
+	default:		/* negative explicit process group */
+		return (killpg1(cp, signum, -pid, 0));
+	}
+	/* NOTREACHED */
+}
+
+int
 sys_kill(struct proc *cp, void *v, register_t *retval)
 {
 	struct sys_kill_args /* {