linux-kernel - Re: [PATCH v5] fs: clear file privilege bits when mmap writing

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Message-ID: <20151210193351.GE20997@ZenIV.linux.org.uk>
Date:	Thu, 10 Dec 2015 19:33:51 +0000
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Willy Tarreau <w@....eu>
Cc:	Kees Cook <keescook@...omium.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jan Kara <jack@...e.cz>, yalin wang <yalin.wang2010@...il.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
	Linux-MM <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v5] fs: clear file privilege bits when mmap writing

On Thu, Dec 10, 2015 at 07:16:11PM +0100, Willy Tarreau wrote:

> > Is f_flags safe to write like this without holding a lock?
> 
> Unfortunately I have no idea. I've seen places where it's written without
> taking a lock such as in blkdev_open() and I don't think that this one is
> called with a lock held.

In any ->open() we obviously have nobody else able to find that struct file,
let alone modify it, so there the damn thing is essentially caller-private
and no locking is needed.
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