kernel/params.c: fix the maximum length in param_get_string

The length parameter of strlcpy() is supposed to reflect the size of the
target buffer, not of the source string.  Harmless in this case as the
buffer is PAGE_SIZE long and the source string is always much shorter than
this, but conceptually wrong, so let's fix it.

Link: http://lkml.kernel.org/r/20170928162515.24846b4f@endymionSigned-off-by: NJean Delvare <jdelvare@suse.de>
Acked-by: NIngo Molnar <mingo@kernel.org>
Cc: Baoquan He <bhe@redhat.com>
Cc: Michal Hocko <mhocko@suse.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

kernel/params.c

@@ -507,7 +507,7 @@ EXPORT_SYMBOL(param_set_copystring);
 int param_get_string(char *buffer, const struct kernel_param *kp)
 {
 	const struct kparam_string *kps = kp->str;
-	return strlcpy(buffer, kps->string, kps->maxlen);
+	return strlcpy(buffer, kps->string, PAGE_SIZE);
 }
 EXPORT_SYMBOL(param_get_string);