Re: [RFC] situation with csum_and_copy_... API

From: Al Viro <viro@ZenIV.linux.org.uk>
Date: Tue, 18 Nov 2014 21:23:07 +0000

On Tue, Nov 18, 2014 at 12:49:13PM -0800, Linus Torvalds wrote:

quoted

"access_ok()" isn't that expensive, and removing them as unnecessary
is fraught with errors. We've had several cases of "oops, we used
__get_user() in a loop, because it generates much better code, but
we'd forgotten to do access_ok(), so now people can read kernel data".

OK...  If netdev folks can live with that for now, I've no problem with
dropping 3/5.  However, I really think we need a variant of csum-and-copy
that would _not_ bother with access_ok() longer term.  That can wait, though...

I think because of the way Al verifies things at the top level, and
how we structure access to these msg->msg_iov so strictly, these cases
of access_ok() really can safely go.

But that is just my opinion, and yes I do acknowledge that we've had
serious holes in this area in the past.