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

On Sun, Jun 24, 2018 at 3:48 AM David Miller [off-list ref] wrote:

From: Al Viro <viro@ZenIV.linux.org.uk>
Date: Sat, 23 Jun 2018 23:21:07 +0100

quoted

BTW, I wonder if the life would be simpler with do_ipv6_setsockopt() doing
the copy-in and verifying ipv6_optlen(*hdr) <= newoptlen; that would've
simplified ipv6_renew_option{,s}() quite a bit and completely eliminated
ipv6_renew_options_kern()...

I agree that this makes things a lot simpler.

I had looked at moving the userspace copy up, but feared it was a bit
too invasive.  It sounds like you are open to the idea so I'll code
something up.

One thing that drives me crazy though is this inherit stuff:

quoted

+     ipv6_renew_option(newtype == IPV6_HOPOPTS ? newopt :
+                             opt ? opt->hopopt : NULL,

Why don't we pass the type into ipv6_renew_option() and have it
do this pointer dance instead?

That's going to definitely be easier to read.

I agree, that struck me as a little odd.  I'll rework that too.  I'll
send you guys something this week to take a look at.

Thanks.

I don't know enough about this code to give feedback about the
option length handling wrt. copies, sorry.

-- 
paul moore
www.paul-moore.com