linux-kernel - Re: [PATCH v3 3/3] namei: aggressively check for nd->root escape on ".." resolution

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20181013090432.GV32577@ZenIV.linux.org.uk>
Date:   Sat, 13 Oct 2018 10:04:32 +0100
From:   Al Viro <viro@...IV.linux.org.uk>
To:     Aleksa Sarai <cyphar@...har.com>
Cc:     Aleksa Sarai <asarai@...e.de>, Jann Horn <jannh@...gle.com>,
        "Eric W. Biederman" <ebiederm@...ssion.com>, jlayton@...nel.org,
        Bruce Fields <bfields@...ldses.org>,
        Arnd Bergmann <arnd@...db.de>,
        Andy Lutomirski <luto@...nel.org>,
        David Howells <dhowells@...hat.com>, christian@...uner.io,
        Tycho Andersen <tycho@...ho.ws>,
        David Drysdale <drysdale@...gle.com>, dev@...ncontainers.org,
        containers@...ts.linux-foundation.org,
        linux-fsdevel@...r.kernel.org,
        kernel list <linux-kernel@...r.kernel.org>,
        linux-arch <linux-arch@...r.kernel.org>,
        Linux API <linux-api@...r.kernel.org>
Subject: Re: [PATCH v3 3/3] namei: aggressively check for nd->root escape on
 ".." resolution

On Sat, Oct 13, 2018 at 07:53:26PM +1100, Aleksa Sarai wrote:

> I didn't know about path_is_under() -- I just checked and it appears to
> not take &rename_lock? From my understanding, in order to protect
> against the rename attack you need to take &rename_lock (or check
> against &rename_lock at least and retry if it changed).
> 
> I could definitely use path_is_under() if you prefer, though I think
> that in this case we'd need to take &rename_lock (right?). Also is there
> a speed issue with taking the write-side of a seqlock when we are just
> reading -- is this more efficient than doing a retry like in __d_path?

???

1) it uses is_subdir(), which does deal with rename_lock
2) what it does is taking mount_lock.lock.  I.e. the same
thing as the second retry in __d_path().  _If_ it shows
up in profiles, we can switch it to read_seqbegin_or_lock(),
but I'd like to see the profiling data first.