Date: Fri, 22 Jun 2012 15:20:29 -0700
From: Andrew Morton <akpm@linux-foundation.org>
To: Kees Cook <keescook@chromium.org>
Cc: linux-kernel@vger.kernel.org, Alan Cox <alan@linux.intel.com>,
        "Eric W. Biederman" <ebiederm@xmission.com>,
        Alexander Viro <viro@zeniv.linux.org.uk>,
        Rob Landley <rob@landley.net>, Ingo Molnar <mingo@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Doug Ledford <dledford@redhat.com>,
        Marcel Holtmann <marcel@holtmann.org>,
        Serge Hallyn <serge.hallyn@canonical.com>,
        Joe Korty <joe.korty@ccur.com>, David Howells <dhowells@redhat.com>,
        James Morris <james.l.morris@oracle.com>, linux-doc@vger.kernel.org,
        linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH v3] fs: introduce pipe-only dump mode suid_dumpable=3
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On Fri, 22 Jun 2012 15:07:45 -0700
Kees Cook <keescook@chromium.org> wrote:

> mode=2 to disk _should_ break, is my point.

And my point is that we should at least tell people that we broke it. 
I don't believe that returning an EINVAL from the write() is
sufficient.  Because it introduces a high risk that people will run
misconfigured systems for lengthy periods and it will cause them to
have to do a *lot* of work once they discover that their system is
misbehaving.

So if we really really must instabreak back-compatibility, we should
shout loudly into syslog about it: tell people that their system is
broken and tell them what to do about it.

And we should explain and justify this extraordinary action in the
patch changelog.
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