linux-kernel - Re: [RFC] call_with

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Message-ID: <CA+55aFxh62Yttq-W2Cr_YQQ5tAL1xjijjnaz1-zdZNqZPQFM0g@mail.gmail.com>
Date:   Wed, 18 Jul 2018 11:19:18 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Al Viro <viro@...iv.linux.org.uk>
Cc:     Miklos Szeredi <mszeredi@...hat.com>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [RFC] call_with_creds()

On Wed, Jul 18, 2018 at 11:13 AM Al Viro <viro@...iv.linux.org.uk> wrote:
>
> Linus, David - do you have any objections to the above?

I damn well do.

I explained earlier why it's wrong and fragile, and why it can just
cause the *reverse* security problem if you do it wrong. So now you
take a subtle bug, and make it even more subtle, and encourage people
to do this known-broken model of using creds at IO time.

No.

Some debugging option to just clear current->creds entirely and catch
mis-uses, sure. But saying "we have shit buggy garbage in random write
functions, so we'll just paper over it"? No.

                 Linus