Date: Thu, 26 Sep 2013 04:02:54 +0100 From: Al Viro <viro@...IV.linux.org.uk> To: Linus Torvalds <torvalds@...ux-foundation.org> Cc: Djalal Harouni <tixxdz@...ndz.org>, "Eric W. Biederman" <ebiederm@...ssion.com>, Kees Cook <keescook@...omium.org>, Andrew Morton <akpm@...ux-foundation.org>, Ingo Molnar <mingo@...nel.org>, "Serge E. Hallyn" <serge.hallyn@...ntu.com>, Cyrill Gorcunov <gorcunov@...nvz.org>, LKML <linux-kernel@...r.kernel.org>, linux-fsdevel <linux-fsdevel@...r.kernel.org>, "kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com>, tixxdz@...il.com Subject: Re: [PATCH 04/12] seq_file: Make seq_file able to access the file's opener cred On Wed, Sep 25, 2013 at 05:22:51PM -0700, Linus Torvalds wrote: > On Wed, Sep 25, 2013 at 1:14 PM, Djalal Harouni <tixxdz@...ndz.org> wrote: > > > > Therefor add the f_cred field to the seq_file struct and a helper > > seq_f_cred() to return it. > > I hate how you've split up this patch from the next one that actually > _initializes_ the new field. > > The two patches should have been one. > > I think the patch should also remove the 'user_ns' member, since it's > now available as f_cred->user_ns. > > I also suspect that it would be better to just make the the new > seq_file member point to the 'struct file' instead. Sure, it's an > extra level of indirection, but the lifetime of f_cred is not as clear > otherwise. You don't increment the reference count, which is correct > *only* because 'seq_file' has the same lifetime as 'struct file', and > thus the reference count from struct file for the f_cred is > sufficient. That's better than f_cred (or user_ns, for that matter), but... I'm afraid that it'll get abused very soon. And I don't understand the argument about the lifetime rules - what makes struct file ones different from struct cred ones in that respect? Except that in this case it's really obvious that we can't grab a reference, that is...
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