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    SubjectRe: [RFC] situation with csum_and_copy_... API
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    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:
    >> "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.


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