Re: [PATCH] ipv6: avoid copy_from_user() via ipv6_renew_options_kern()

On Sat, Jun 23, 2018 at 10:57:06AM +0900, David Miller wrote:

From: Paul Moore <redacted>
Date: Fri, 22 Jun 2018 17:18:20 -0400

quoted

-	const mm_segment_t old_fs = get_fs();
-
-	set_fs(KERNEL_DS);
-	ret_val = ipv6_renew_options(sk, opt, newtype,
-				     (struct ipv6_opt_hdr __user *)newopt,
-				     newoptlen);
-	set_fs(old_fs);

So is it really the case that the traditional construct:

	set_fs(KERNEL_DS);
	... copy_{from,to}_user(...);
	set_fs(old_fs);

is no longer allowed?

s/no longer allowed/best avoided/, but IMO in this case the replacement is
too ugly to live ;-/