linux-kernel - [PATCH v2 1/1] kernel/watchdog: always restore watchdog_softlockup(,hardlockup)_user

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives
Hash Suite: Windows password security audit tool. GUI, reports in PDF.
[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <20240906094700.GA30052@didi-ThinkCentre-M930t-N000>
Date: Fri, 6 Sep 2024 17:47:00 +0800
From: Tio Zhang <tiozhang@...iglobal.com>
To: <dianders@...omium.org>
CC: <akpm@...ux-foundation.org>, <bristot@...hat.com>, <bsegall@...gle.com>,
	<dietmar.eggemann@....com>, <john.ogness@...utronix.de>,
	<juri.lelli@...hat.com>, <kjlx@...pleofstupid.com>,
	<linux-kernel@...r.kernel.org>, <linux@...ssschuh.net>,
	<lizhe.67@...edance.com>, <mcgrof@...nel.org>, <mgorman@...e.de>,
	<mingo@...hat.com>, <peterz@...radead.org>, <rostedt@...dmis.org>,
	<tglx@...utronix.de>, <tiozhang@...iglobal.com>,
	<vincent.guittot@...aro.org>, <vschneid@...hat.com>, <zyhtheonly@...il.com>,
	<zyhtheonly@...h.net>
Subject: [PATCH v2 1/1] kernel/watchdog: always restore
 watchdog_softlockup(,hardlockup)_user_enabled after proc show

Otherwise when watchdog_enabled becomes 0,
watchdog_softlockup(,hardlockup)_user_enabled will changes to 0 after
proc show.

Steps to reproduce:

  step 1:
  # cat /proc/sys/kernel/*watchdog
  1
  1
  1

  | name                             | value
  |----------------------------------|--------------------------
  | watchdog_enabled                 | 1
  |----------------------------------|--------------------------
  | watchdog_hardlockup_user_enabled | 1
  |----------------------------------|--------------------------
  | watchdog_softlockup_user_enabled | 1
  |----------------------------------|--------------------------
  | watchdog_user_enabled            | 1
  |----------------------------------|--------------------------

  step 2:
  # echo 0 > /proc/sys/kernel/watchdog

  | name                             | value
  |----------------------------------|--------------------------
  | watchdog_enabled                 | 0
  |----------------------------------|--------------------------
  | watchdog_hardlockup_user_enabled | 1
  |----------------------------------|--------------------------
  | watchdog_softlockup_user_enabled | 1
  |----------------------------------|--------------------------
  | watchdog_user_enabled            | 0
  |----------------------------------|--------------------------

  step 3:
  # cat /proc/sys/kernel/*watchdog
  0
  0
  0

  | name                             | value
  |----------------------------------|--------------------------
  | watchdog_enabled                 | 0
  |----------------------------------|--------------------------
  | watchdog_hardlockup_user_enabled | 0
  |----------------------------------|--------------------------
  | watchdog_softlockup_user_enabled | 0
  |----------------------------------|--------------------------
  | watchdog_user_enabled            | 0
  |----------------------------------|--------------------------

  step 4:
  # echo 1 > /proc/sys/kernel/watchdog

  | name                             | value
  |----------------------------------|--------------------------
  | watchdog_enabled                 | 0
  |----------------------------------|--------------------------
  | watchdog_hardlockup_user_enabled | 0
  |----------------------------------|--------------------------
  | watchdog_softlockup_user_enabled | 0
  |----------------------------------|--------------------------
  | watchdog_user_enabled            | 0
  |----------------------------------|--------------------------

  step 5:
  # cat /proc/sys/kernel/*watchdog
  0
  0
  0

If we dont do "step 3", do "step 4" right after "step 2", it will be

  | name                             | value
  |----------------------------------|--------------------------
  | watchdog_enabled                 | 1
  |----------------------------------|--------------------------
  | watchdog_hardlockup_user_enabled | 1
  |----------------------------------|--------------------------
  | watchdog_softlockup_user_enabled | 1
  |----------------------------------|--------------------------
  | watchdog_user_enabled            | 1
  |----------------------------------|--------------------------

then everything works correctly.

So this patch fix "step 3"'s value into

| name                             | value
|----------------------------------|--------------------------
| watchdog_enabled                 | 0
|----------------------------------|--------------------------
| watchdog_hardlockup_user_enabled | 1
|----------------------------------|--------------------------
| watchdog_softlockup_user_enabled | 1
|----------------------------------|--------------------------
| watchdog_user_enabled            | 0
|----------------------------------|--------------------------

And still print 0 as before.

Signed-off-by: Tio Zhang <tiozhang@...iglobal.com>
---
 kernel/watchdog.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/kernel/watchdog.c b/kernel/watchdog.c
index 51915b44ac73..ade69b2319f6 100644
--- a/kernel/watchdog.c
+++ b/kernel/watchdog.c
@@ -990,6 +990,7 @@ static int proc_watchdog_common(int which, struct ctl_table *table, int write,
 
 	mutex_lock(&watchdog_mutex);
 
+	old = *param;
 	if (!write) {
 		/*
 		 * On read synchronize the userspace interface. This is a
@@ -997,8 +998,8 @@ static int proc_watchdog_common(int which, struct ctl_table *table, int write,
 		 */
 		*param = (watchdog_enabled & which) != 0;
 		err = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
+		*param = old;
 	} else {
-		old = READ_ONCE(*param);
 		err = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
 		if (!err && old != READ_ONCE(*param))
 			proc_watchdog_update();
-- 
2.17.1