[PATCH] sysctl: do not allow a 64bit value write in a 32bit knob

[Aristeu Rozanski <aris@redhat.com>]

Writing to a sysctl file that uses proc_dointvec_minmax like user/max_uts_namespaces
a larger than 32 bit value won't cause an error as expected but instead will zero
its value:
	# echo 214748364800000 > max_uts_namespaces
	# cat max_uts_namespaces
	0

This patches fixes it.

Signed-off-by: Aristeu Rozanski <aris@redhat.com>
Cc: "Luis R. Rodriguez" <mcgrof@kernel.org>
Cc: Kees Cook <keescook@chromium.org>

diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index 4ac9b9a..243f277 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -2486,7 +2486,8 @@ static int do_proc_dointvec_minmax_conv(bool *negp, unsigned long *lvalp,
 	if (write) {
 		int val = *negp ? -*lvalp : *lvalp;
 		if ((param->min && *param->min > val) ||
-		    (param->max && *param->max < val))
+		    (param->max && *param->max < val) ||
+		    *lvalp >> (sizeof(int) * 8))
 			return -EINVAL;
 		*valp = val;
 	} else {