svn commit: r324736 - head/sys/kern

[Mateusz Guzik]

Author: mjg
Date: Thu Oct 19 01:38:31 2017
New Revision: 324736
URL: https://svnweb.freebsd.org/changeset/base/324736

Log:
  sysctl: only take mem lock if oldlen is > 4 * PAGE_SIZE
  
  The previous limit of just one page is hit by ps.
  
  The entire mechanism should be reworked, if not whacked. It seems the intent
  is to reduce kernel dos-ability - some handlers wire the amount of memory
  passed here. Handlers should probably stop wiring in the first place or in
  the worst case indicate they are doing so so that the check is done only if
  necessary. It should also probably be a counter, not a lock.
  
  MFC after:	1 week

Modified:
  head/sys/kern/kern_sysctl.c

Modified: head/sys/kern/kern_sysctl.c
==============================================================================
--- head/sys/kern/kern_sysctl.c	Thu Oct 19 00:46:15 2017	(r324735)
+++ head/sys/kern/kern_sysctl.c	Thu Oct 19 01:38:31 2017	(r324736)
@@ -2109,12 +2109,11 @@ userland_sysctl(struct thread *td, int *name, u_int na
 	if (KTRPOINT(curthread, KTR_SYSCTL))
 		ktrsysctl(name, namelen);
 #endif
-
-	if (req.oldptr && req.oldlen > PAGE_SIZE) {
+	memlocked = 0;
+	if (req.oldptr && req.oldlen > 4 * PAGE_SIZE) {
 		memlocked = 1;
 		sx_xlock(&sysctlmemlock);
-	} else
-		memlocked = 0;
+	}
 	CURVNET_SET(TD_TO_VNET(td));
 
 	for (;;) {