linux-kernel - [PATCH] sysctl: add bound to panic

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Date:   Thu,  9 Jul 2020 23:22:23 -0400
From:   Changming Liu <charley.ashbringer@...il.com>
To:     keescook@...omium.org
Cc:     mcgrof@...nel.org, yzaikin@...gle.com,
        linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        Changming Liu <charley.ashbringer@...il.com>
Subject: [PATCH] sysctl: add bound to panic_timeout to prevent overflow

Function panic() in kernel/panic.c will use panic_timeout
multiplying 1000 as a loop boundery. So this multiplication
can overflow when panic_timeout is greater than (INT_MAX/1000).
And this results in a zero-delay panic, instead of a huge
timeout as the user intends.

Fix this by adding bound check to make it no bigger than
(INT_MAX/1000).

Signed-off-by: Changming Liu <charley.ashbringer@...il.com>
---
 kernel/sysctl.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index db1ce7a..e60cf04 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -137,6 +137,9 @@ static int minolduid;
 static int ngroups_max = NGROUPS_MAX;
 static const int cap_last_cap = CAP_LAST_CAP;
 
+/* this is needed for setting boundery for panic_timeout to prevent it from overflow*/
+static int panic_time_max = INT_MAX / 1000;
+
 /*
  * This is needed for proc_doulongvec_minmax of sysctl_hung_task_timeout_secs
  * and hung_task_check_interval_secs
@@ -1857,7 +1860,8 @@ static struct ctl_table kern_table[] = {
 		.data		= &panic_timeout,
 		.maxlen		= sizeof(int),
 		.mode		= 0644,
-		.proc_handler	= proc_dointvec,
+		.proc_handler	= proc_dointvec_minmax,
+		.extra2		= &panic_time_max,
 	},
 #ifdef CONFIG_COREDUMP
 	{
-- 
2.7.4