linux-kernel - [PATCH v4 2/2] sysctl: Fix underflow value setting risk in vm

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Message-ID: <20250115132211.25400-3-nicolas.bouchinet@clip-os.org>
Date: Wed, 15 Jan 2025 14:22:09 +0100
From: nicolas.bouchinet@...p-os.org
To: linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org
Cc: Nicolas Bouchinet <nicolas.bouchinet@....gouv.fr>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Jiri Slaby <jirislaby@...nel.org>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Christian Brauner <brauner@...nel.org>,
	Jan Kara <jack@...e.cz>,
	Luis Chamberlain <mcgrof@...nel.org>,
	Kees Cook <kees@...nel.org>,
	Joel Granados <j.granados@...sung.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Neil Horman <nhorman@...driver.com>,
	Lin Feng <linf@...gsu.com>,
	"Theodore Ts'o" <tytso@....edu>
Subject: [PATCH v4 2/2] sysctl: Fix underflow value setting risk in vm_table

From: Nicolas Bouchinet <nicolas.bouchinet@....gouv.fr>

Commit 3b3376f222e3 ("sysctl.c: fix underflow value setting risk in vm_table")
fixes underflow value setting risk in vm_table but misses vdso_enabled
sysctl.

vdso_enabled sysctl is initialized with .extra1 value as SYSCTL_ZERO to
avoid negative value writes but the proc_handler is proc_dointvec and
not proc_dointvec_minmax and thus do not uses .extra1 and .extra2.

The following command thus works :

`# echo -1 > /proc/sys/vm/vdso_enabled`

This patch properly sets the proc_handler to proc_dointvec_minmax.
In addition to .extra1, .extra2 is set to SYSCTL_ONE. The sysctl is
thus bounded between 0 and 1.

Fixes: 3b3376f222e3 ("sysctl.c: fix underflow value setting risk in vm_table")
Signed-off-by: Nicolas Bouchinet <nicolas.bouchinet@....gouv.fr>
Reviewed-by: Jan Kara <jack@...e.cz>
---
 arch/sh/kernel/vsyscall/vsyscall.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/sh/kernel/vsyscall/vsyscall.c b/arch/sh/kernel/vsyscall/vsyscall.c
index d80dd92a483af..1563dcc55fd32 100644
--- a/arch/sh/kernel/vsyscall/vsyscall.c
+++ b/arch/sh/kernel/vsyscall/vsyscall.c
@@ -37,8 +37,9 @@ static const struct ctl_table vdso_table[] = {
 		.data		= &vdso_enabled,
 		.maxlen		= sizeof(vdso_enabled),
 		.mode		= 0644,
-		.proc_handler	= proc_dointvec,
+		.proc_handler	= proc_dointvec_minmax,
 		.extra1		= SYSCTL_ZERO,
+		.extra2		= SYSCTL_ONE,
 	},
 };
 
-- 
2.48.1