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From: Aleksa Sarai <cyphar@cyphar.com>
To: Al Viro <viro@ZenIV.linux.org.uk>
Cc: Aleksa Sarai <asarai@suse.de>, Jann Horn <jannh@google.com>,
	"Eric W. Biederman" <ebiederm@xmission.com>,
	jlayton@kernel.org, Bruce Fields <bfields@fieldses.org>,
	Arnd Bergmann <arnd@arndb.de>, Andy Lutomirski <luto@kernel.org>,
	David Howells <dhowells@redhat.com>,
	christian@brauner.io, Tycho Andersen <tycho@tycho.ws>,
	David Drysdale <drysdale@google.com>,
	dev@opencontainers.org, containers@lists.linux-foundation.org,
	linux-fsdevel@vger.kernel.org,
	kernel list <linux-kernel@vger.kernel.org>,
	linux-arch <linux-arch@vger.kernel.org>,
	Linux API <linux-api@vger.kernel.org>
Subject: Re: [PATCH v3 3/3] namei: aggressively check for nd->root escape on ".." resolution
Date: Sat, 13 Oct 2018 20:27:02 +1100	[thread overview]
Message-ID: <20181013092702.mf4gjnq2cfqhkvah@ryuk> (raw)
In-Reply-To: <20181013090432.GV32577@ZenIV.linux.org.uk>

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On 2018-10-13, Al Viro <viro@ZenIV.linux.org.uk> wrote:
> 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

Oh -- complete brain-fart on my part. Sorry about that.

> 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.

Sure, I'll switch it to use path_is_under().

-- 
Aleksa Sarai
Senior Software Engineer (Containers)
SUSE Linux GmbH
<https://www.cyphar.com/>

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  parent reply	other threads:[~2018-10-13  9:27 UTC|newest]

Thread overview: 32+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-10-09  7:02 [PATCH v3 0/3] namei: implement various lookup restriction AT_* flags Aleksa Sarai
2018-10-09  7:02 ` Aleksa Sarai
2018-10-09  7:02 ` [PATCH v3 1/3] namei: implement O_BENEATH-style " Aleksa Sarai
2018-10-09  7:02   ` Aleksa Sarai
2018-10-13  7:33   ` Al Viro
2018-10-13  7:33     ` Al Viro
2018-10-13  8:05     ` Al Viro
2018-10-13  8:05       ` Al Viro
2018-10-13  8:20       ` Aleksa Sarai
2018-10-13  8:20         ` Aleksa Sarai
2018-10-13  8:09     ` Aleksa Sarai
2018-10-13  8:09       ` Aleksa Sarai
2018-10-09  7:02 ` [PATCH v3 2/3] namei: implement AT_THIS_ROOT chroot-like path resolution Aleksa Sarai
2018-10-09  7:02   ` Aleksa Sarai
2018-10-09  7:02 ` [PATCH v3 3/3] namei: aggressively check for nd->root escape on ".." resolution Aleksa Sarai
2018-10-09  7:02   ` Aleksa Sarai
2018-10-09 15:19   ` Jann Horn
2018-10-09 15:19     ` Jann Horn
2018-10-09 15:37     ` Aleksa Sarai
2018-10-09 15:37       ` Aleksa Sarai
2018-10-09 16:46       ` Jann Horn
2018-10-09 16:46         ` Jann Horn
2018-10-13  8:22       ` Al Viro
2018-10-13  8:22         ` Al Viro
2018-10-13  8:53         ` Aleksa Sarai
2018-10-13  8:53           ` Aleksa Sarai
2018-10-13  9:04           ` Al Viro
2018-10-13  9:04             ` Al Viro
2018-10-13  9:27             ` Aleksa Sarai [this message]
2018-10-13  9:27               ` Aleksa Sarai
2018-10-17 15:23 ` [PATCH v3 0/3] namei: implement various lookup restriction AT_* flags Aleksa Sarai
2018-10-17 15:23   ` Aleksa Sarai

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