[src/trunk]: src/sys/kern PR kern/55251: use of ZFS may trigger kernel memory...

[ad <ad%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/1bc896cc2f6b
branches:  trunk
changeset: 972007:1bc896cc2f6b
user:      ad <ad%NetBSD.org@localhost>
date:      Tue May 12 21:24:29 2020 +0000

description:
PR kern/55251: use of ZFS may trigger kernel memory corruption

mutex_vector_enter(): reload mtx_owner with preemption disabled before
calling mutex_oncpu(), otherwise lwp_dtor() can intervene.

diffstat:

 sys/kern/kern_mutex.c |  12 ++++++++----
 1 files changed, 8 insertions(+), 4 deletions(-)

diffs (36 lines):

diff -r 1f3c4bbe6ff7 -r 1bc896cc2f6b sys/kern/kern_mutex.c
--- a/sys/kern/kern_mutex.c     Tue May 12 20:50:17 2020 +0000
+++ b/sys/kern/kern_mutex.c     Tue May 12 21:24:29 2020 +0000
@@ -1,7 +1,7 @@
-/*     $NetBSD: kern_mutex.c,v 1.90 2020/03/08 00:26:06 chs Exp $      */
+/*     $NetBSD: kern_mutex.c,v 1.91 2020/05/12 21:24:29 ad Exp $       */
 
 /*-
- * Copyright (c) 2002, 2006, 2007, 2008, 2019 The NetBSD Foundation, Inc.
+ * Copyright (c) 2002, 2006, 2007, 2008, 2019, 2020 The NetBSD Foundation, Inc.
  * All rights reserved.
  *
  * This code is derived from software contributed to The NetBSD Foundation
@@ -40,7 +40,7 @@
 #define        __MUTEX_PRIVATE
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: kern_mutex.c,v 1.90 2020/03/08 00:26:06 chs Exp $");
+__KERNEL_RCSID(0, "$NetBSD: kern_mutex.c,v 1.91 2020/05/12 21:24:29 ad Exp $");
 
 #include <sys/param.h>
 #include <sys/atomic.h>
@@ -545,8 +545,12 @@
                /*
                 * Check to see if the owner is running on a processor.
                 * If so, then we should just spin, as the owner will
-                * likely release the lock very soon.
+                * likely release the lock very soon.  Unfortunately
+                * mtx_owner needs to be reloaded here with preemption
+                * now disabled, otherwise the LWP could already have
+                * been freed & destructed (see lwp_dtor()).
                 */
+               owner = mtx->mtx_owner;
                if (mutex_oncpu(owner)) {
                        LOCKSTAT_START_TIMER(lsflag, spintime);
                        count = SPINLOCK_BACKOFF_MIN;