svn commit: r323390 - head/sys/kern

[Dag-Erling Smørgrav]

Author: des
Date: Sun Sep 10 15:01:29 2017
New Revision: 323390
URL: https://svnweb.freebsd.org/changeset/base/323390

Log:
  If the user tries to set kern.randompid to 1 (which is meaningless), set
  it to a random value between 100 and 1123, rather than 0 as before.
  
  Submitted by:	Marie Helene Kvello-Aune <marieheleneka at gmail.com>
  MFC after:	1 week
  Differential Revision:	https://reviews.freebsd.org/D5336

Modified:
  head/sys/kern/kern_fork.c

Modified: head/sys/kern/kern_fork.c
==============================================================================
--- head/sys/kern/kern_fork.c	Sun Sep 10 13:53:42 2017	(r323389)
+++ head/sys/kern/kern_fork.c	Sun Sep 10 15:01:29 2017	(r323390)
@@ -208,20 +208,26 @@ sysctl_kern_randompid(SYSCTL_HANDLER_ARGS)
 	pid = randompid;
 	error = sysctl_handle_int(oidp, &pid, 0, req);
 	if (error == 0 && req->newptr != NULL) {
-		if (pid < 0 || pid > pid_max - 100)	/* out of range */
-			pid = pid_max - 100;
-		else if (pid < 2)			/* NOP */
-			pid = 0;
-		else if (pid < 100)			/* Make it reasonable */
-			pid = 100;
-		randompid = pid;
+		if (pid == 0)
+			randompid = 0;
+		else if (pid == 1)
+			/* generate a random PID modulus between 100 and 1123 */
+			randompid = 100 + arc4random() % 1024;
+		else if (pid < 0 || pid > pid_max - 100)
+			/* out of range */
+			randompid = pid_max - 100;
+		else if (pid < 100)	 
+			/* Make it reasonable */
+			randompid = 100;
+		else
+			randompid = pid;
 	}
 	sx_xunlock(&allproc_lock);
 	return (error);
 }
 
 SYSCTL_PROC(_kern, OID_AUTO, randompid, CTLTYPE_INT|CTLFLAG_RW,
-    0, 0, sysctl_kern_randompid, "I", "Random PID modulus");
+    0, 0, sysctl_kern_randompid, "I", "Random PID modulus. Special values: 0: disable, 1: choose random value");
 
 static int
 fork_findpid(int flags)