sysctl: Fix underflow value setting risk in vm_table

Commit 3b3376f ("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: 3b3376f ("sysctl.c: fix underflow value setting risk in vm_table")
Signed-off-by: Nicolas Bouchinet <nicolas.bouchinet@ssi.gouv.fr>
Reviewed-by: Jan Kara <jack@suse.cz>
Reviewed-by: Kees Cook <kees@kernel.org>
Signed-off-by: Joel Granados <joel.granados@kernel.org>

Author: nbouchinet-anssi

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,
 	},
 };