Module Name: src
Committed By: riastradh
Date: Sun Apr 16 11:14:58 UTC 2023
Modified Files:
src/sys/kern: subr_autoconf.c
Log Message:
autoconf(9): Avoid potential ABA bug in config_makeroom.
When we unlock alldevs_lock to allocate a new cd_devs array nsp,
other threads may have:
1. freed the old one (osp),
2. done some other memory allocation,
3. allocated a new _larger_ array whose address happens to concide
with osp (e.g., in (2) the page was recycled for a different pool
cache), and
4. updated cd_devs back to osp but increased cd_ndevs.
In that case, the memory may be corrupted: we try to copy the wrong
number of device_t pointers into nsp and we free osp with the wrong
(stale) length.
Avoid this by checking whether cd_ndevs has changed too -- if not,
osp might have been recycled but at least the lengths we're about to
copy and free are still correct so there's no harm in an ABA
situation.
XXX pullup-8
XXX pullup-9
XXX pullup-10
To generate a diff of this commit:
cvs rdiff -u -r1.307 -r1.308 src/sys/kern/subr_autoconf.c
Please note that diffs are not public domain; they are subject to the
copyright notices on the relevant files.
Modified files:
Index: src/sys/kern/subr_autoconf.c
diff -u src/sys/kern/subr_autoconf.c:1.307 src/sys/kern/subr_autoconf.c:1.308
--- src/sys/kern/subr_autoconf.c:1.307 Wed Feb 22 17:00:16 2023
+++ src/sys/kern/subr_autoconf.c Sun Apr 16 11:14:58 2023
@@ -1,4 +1,4 @@
-/* $NetBSD: subr_autoconf.c,v 1.307 2023/02/22 17:00:16 riastradh Exp $ */
+/* $NetBSD: subr_autoconf.c,v 1.308 2023/04/16 11:14:58 riastradh Exp $ */
/*
* Copyright (c) 1996, 2000 Christopher G. Demetriou
@@ -77,7 +77,7 @@
*/
#include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: subr_autoconf.c,v 1.307 2023/02/22 17:00:16 riastradh Exp $");
+__KERNEL_RCSID(0, "$NetBSD: subr_autoconf.c,v 1.308 2023/04/16 11:14:58 riastradh Exp $");
#ifdef _KERNEL_OPT
#include "opt_ddb.h"
@@ -1357,7 +1357,7 @@ config_makeroom(int n, struct cfdriver *
* If another thread moved the array while we did
* not hold alldevs_lock, try again.
*/
- if (cd->cd_devs != osp) {
+ if (cd->cd_devs != osp || cd->cd_ndevs != ondevs) {
mutex_exit(&alldevs_lock);
kmem_free(nsp, sizeof(device_t) * nndevs);
mutex_enter(&alldevs_lock);
