linux-kernel - RE: [PATCH v3 2/2] Protected O_CREAT open in sticky directories

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Message-ID: <33dcc007e92349999ce77bf45825be22@AcuMS.aculab.com>
Date:   Fri, 24 Nov 2017 10:53:11 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Alan Cox' <gnomes@...rguk.ukuu.org.uk>,
        Salvatore Mesoraca <s.mesoraca16@...il.com>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Kernel Hardening" <kernel-hardening@...ts.openwall.com>,
        "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
        "Alexander Viro" <viro@...iv.linux.org.uk>,
        Jann Horn <jannh@...gle.com>,
        Kees Cook <keescook@...omium.org>,
        Solar Designer <solar@...nwall.com>,
        "Eric W. Biederman" <ebiederm@...ssion.com>
Subject: RE: [PATCH v3 2/2] Protected O_CREAT open in sticky directories

From: Alan Cox
> Sent: 22 November 2017 16:52
> 
> On Wed, 22 Nov 2017 09:01:46 +0100
> Salvatore Mesoraca <s.mesoraca16@...il.com> wrote:
> 
> > Disallows O_CREAT open missing the O_EXCL flag, in world or
> > group writable directories, even if the file doesn't exist yet.
> > With few exceptions (e.g. shared lock files based on flock())
> 
> Enough exceptions to make it a bad idea.
> 
> Firstly if you care this much *stop* having shared writable directories.
> We have namespaces, you don't need them. You can give every user their
> own /tmp etc.

Looks like a very bad idea to me as well.

Doesn't this stop all shell redirects into a shared /tmp ?
I'm pretty sure most programs use O_CREAT | O_TRUNC for output
files - they'll all stop working.

If there are some directories where you need to force O_EXCL you
need to make it a property of the directory, not the kernel.

	David