Add a sysctl kern.pid_max, which limits the maximum pid the system is

allowed to allocate, and corresponding tunable with the same
name. Note that existing processes with higher pids are left intact.

MFC after:	1 week

1 files changed, 24 insertions, 0 deletions

diff --git a/sys/kern/kern_mib.c b/sys/kern/kern_mib.c
index 75b3af936d0e..f6ab3a4a5526 100644
--- a/sys/kern/kern_mib.c
+++ b/sys/kern/kern_mib.c
@@ -499,6 +499,30 @@ SYSCTL_INT(_debug_sizeof, OID_AUTO, vnode, CTLFLAG_RD,
 SYSCTL_INT(_debug_sizeof, OID_AUTO, proc, CTLFLAG_RD,
     0, sizeof(struct proc), "sizeof(struct proc)");
 
+static int
+sysctl_kern_pid_max(SYSCTL_HANDLER_ARGS)
+{
+	int error, pm;
+
+	pm = pid_max;
+	error = sysctl_handle_int(oidp, &pm, 0, req);
+	if (error || !req->newptr)
+		return (error);
+	sx_xlock(&proctree_lock);
+	sx_xlock(&allproc_lock);
+	/* Only permit the values less then PID_MAX. */
+	if (pm > PID_MAX)
+		error = EINVAL;
+	else
+		pid_max = pm;
+	sx_xunlock(&allproc_lock);
+	sx_xunlock(&proctree_lock);
+	return (error);
+}
+SYSCTL_PROC(_kern, OID_AUTO, pid_max, CTLTYPE_INT | CTLFLAG_RW | CTLFLAG_TUN |
+    CTLFLAG_MPSAFE, 0, 0, sysctl_kern_pid_max, "I",
+    "Maximum allowed pid");
+
 #include <sys/bio.h>
 #include <sys/buf.h>
 SYSCTL_INT(_debug_sizeof, OID_AUTO, bio, CTLFLAG_RD,