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Message-ID: <20151210202749.GF20997@ZenIV.linux.org.uk>
Date: Thu, 10 Dec 2015 20:27:49 +0000
From: Al Viro <viro@...IV.linux.org.uk>
To: Kees Cook <keescook@...omium.org>
Cc: Willy Tarreau <w@....eu>,
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 11:47:18AM -0800, Kees Cook wrote:
> In open, sure, but what about under mm/memory.c where we're trying to
> twiddle it from vma->file->f_flags as in my patch? That seemed like it
> would want atomic safety.
Sigh... Again, I'm not at all convinced that this is the right approach,
but generally you need ->f_lock. And in situations where the bit can
go only off->on, check it lockless, skip the whole thing entirely if it's
already set and grab the spinlock otherwise.
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