From: Al Viro <viro@ZenIV.linux.org.uk>
To: Aleksa Sarai <asarai@suse.de>
Cc: Jann Horn <jannh@google.com>,
cyphar@cyphar.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 09:22:10 +0100 [thread overview]
Message-ID: <20181013082210.GU32577@ZenIV.linux.org.uk> (raw)
In-Reply-To: <20181009153728.2altaqxclntvyc7b@mikami>
On Wed, Oct 10, 2018 at 02:37:28AM +1100, Aleksa Sarai wrote:
> > > +static inline int nd_alloc_dpathbuf(struct nameidata *nd)
> > > +{
> > > + if (unlikely(!nd->dpathbuf)) {
> > > + if (nd->flags & LOOKUP_RCU) {
> > > + nd->dpathbuf = kmalloc(PATH_MAX, GFP_ATOMIC);
> > > + if (unlikely(!nd->dpathbuf))
> > > + return -ECHILD;
> > > + } else {
> > > + nd->dpathbuf = kmalloc(PATH_MAX, GFP_KERNEL);
> > > + if (unlikely(!nd->dpathbuf))
> > > + return -ENOMEM;
> > > + }
> > > + }
> > > + return 0;
> > > +}
> >
> > Note that a fixed-size path buffer means that if the path is very
> > long, e.g. because you followed long symlinks on the way down, this
> > can cause lookup failures.
>
> This is already an issue with __d_path (even if the buffer was larger)
> because it will not output a path longer than PATH_MAX. I imagine this
> is a pretty strong argument for why we should refactor __d_path so that
> we can *just* use the escape checking to avoid -ENAMETOOLONG.
Let me get it straight - the whole point of that buffer is to check
if __d_path() returns NULL? So you allocate it so that you would have
place to copy the path components into... only to have them completely
ignored?
How is that different from path_is_under()?
next prev parent reply other threads:[~2018-10-13 8:22 UTC|newest]
Thread overview: 16+ 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 ` [PATCH v3 1/3] namei: implement O_BENEATH-style " Aleksa Sarai
2018-10-13 7:33 ` Al Viro
2018-10-13 8:05 ` Al Viro
2018-10-13 8:20 ` 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 ` [PATCH v3 3/3] namei: aggressively check for nd->root escape on ".." resolution Aleksa Sarai
2018-10-09 15:19 ` Jann Horn
2018-10-09 15:37 ` Aleksa Sarai
2018-10-09 16:46 ` Jann Horn
2018-10-13 8:22 ` Al Viro [this message]
2018-10-13 8:53 ` Aleksa Sarai
2018-10-13 9:04 ` Al Viro
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
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