From mboxrd@z Thu Jan  1 00:00:00 1970
From: Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: new ...at() flag: AT_NO_JUMPS
Date: Thu, 4 May 2017 20:46:49 -0700
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 <20170505003030.GM29622@ZenIV.linux.org.uk> <CAG48ez1jzNvxB+bfOBnERFGp=oMM0vHWuLD6EULmne3R6xa53w@mail.gmail.com>
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To: Jann Horn <jannh@google.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>, Linux API <linux-api@vger.kernel.org>, Linux Kernel Mailing List <linux-kernel@vger.kernel.org>, linux-fsdevel <linux-fsdevel@vger.kernel.org>, David Drysdale <drysdale@google.com>
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On Thu, May 4, 2017 at 7:47 PM, Jann Horn <jannh@google.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