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Date:   Thu, 4 May 2017 20:46:49 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Jann Horn <jannh@...gle.com>
Cc:     Al Viro <viro@...iv.linux.org.uk>,
        Linux API <linux-api@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        David Drysdale <drysdale@...gle.com>
Subject: Re: new ...at() flag: AT_NO_JUMPS

On Thu, May 4, 2017 at 7:47 PM, Jann Horn <jannh@...gle.com> wrote:
>
> Thread 1 starts an AT_BENEATH path walk using an O_PATH fd
> pointing to /srv/www/example.org/foo; the path given to the syscall is
> "bar/../../../../etc/passwd". The path walk enters the "bar" directory.
> Thread 2 moves /srv/www/example.org/foo/bar to
> /srv/www/example.org/bar.
> Thread 1 processes the rest of the path ("../../../../etc/passwd"), never
> hitting /srv/www/example.org/foo in the process.
>
> I'm not really familiar with the VFS internals, but from a coarse look
> at the patch, it seems like it wouldn't block this?

I think you're right.

I guess it would be safe for the RCU case due to the sequence number
check, but not the non-RCU case.

Al?

                 Linus

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