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From: "Richard W.M. Jones" <rjones@redhat.com>
To: Stefano Brivio <sbrivio@redhat.com>
Cc: David Gibson <david@gibson.dropbear.id.au>,
	passt-dev@passt.top, Minxi Hou <mhou@redhat.com>
Subject: Re: [PATCH 7/8] conf, passt, tap: Open socket and PID files before switching UID/GID
Date: Thu, 20 Jun 2024 13:47:31 +0100	[thread overview]
Message-ID: <20240620124730.GC1450@redhat.com> (raw)
In-Reply-To: <20240620141253.7e6d3855@elisabeth>

On Thu, Jun 20, 2024 at 02:12:53PM +0200, Stefano Brivio wrote:
> On Thu, 20 Jun 2024 12:30:54 +0100
> "Richard W.M. Jones" <rjones@redhat.com> wrote:
> 
> > On Wed, May 29, 2024 at 12:35:24PM +1000, David Gibson wrote:
> > > On Wed, May 22, 2024 at 10:59:10PM +0200, Stefano Brivio wrote:  
> > > > Otherwise, if the user runs us as root, and gives us paths that are
> > > > only accessible by root, we'll fail to open them, which might in turn
> > > > encourage users to change permissions or ownerships: definitely a bad
> > > > idea in terms of security.
> > > > 
> > > > Reported-by: Minxi Hou <mhou@redhat.com>
> > > > Reported-by: Richard W.M. Jones <rjones@redhat.com>
> > > > Signed-off-by: Stefano Brivio <sbrivio@redhat.com>  
> > > 
> > > Looking at this I did notice a pre-existing, well, maybe not bug
> > > exactly, but possibly surprising behaviour, which makes me a
> > > bit more nervous now that we can invoke it as root.
> > > 
> > > tap_sock_unix_open() will silently truncate the given socket path to
> > > the maximum length for a Unix socket.  Which means we could bind(),
> > > but also unlink() a path that's not exactly the same as the one the
> > > one the user requested.  I don't immediately see a way to exploit
> > > that, but it's the sort of thing that makes me nervous.  I think we
> > > should instead outright fail if the given socket path is too long.  
> > 
> > Yes, agreed.
> > 
> > It seems as if the latest passt code still does this.  Do you want me
> > to open a bug about it?
> 
> Yes, please, that, or a patch :)

While I was testing this, I found we do seem to check it:

https://passt.top/passt/tree/conf.c#n1446

Rich.

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
Read my programming and virtualization blog: http://rwmj.wordpress.com
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bindings from many languages.  http://libguestfs.org


  reply	other threads:[~2024-06-20 12:47 UTC|newest]

Thread overview: 29+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2024-05-22 20:59 [PATCH 0/8] Open socket and PID files as root, before switching Stefano Brivio
2024-05-22 20:59 ` [PATCH 1/8] conf: Don't lecture user about starting us as root Stefano Brivio
2024-05-23  1:45   ` David Gibson
2024-05-23  9:52   ` Richard W.M. Jones
2024-05-22 20:59 ` [PATCH 2/8] tap: Move all-ones initialisation of mac_guest to tap_sock_init() Stefano Brivio
2024-05-23  1:46   ` David Gibson
2024-05-23  9:59   ` Richard W.M. Jones
2024-05-23 10:03     ` Richard W.M. Jones
2024-05-22 20:59 ` [PATCH 3/8] passt, tap: Don't use -1 as uninitialised value for fd_tap_listen Stefano Brivio
2024-05-23  1:48   ` David Gibson
2024-05-22 20:59 ` [PATCH 4/8] tap: Split tap_sock_unix_init() into opening and listening parts Stefano Brivio
2024-05-23 10:05   ` Richard W.M. Jones
2024-05-28  7:01   ` David Gibson
2024-05-22 20:59 ` [PATCH 5/8] util: Rename write_pidfile() to pidfile_write() Stefano Brivio
2024-05-23 10:06   ` Richard W.M. Jones
2024-05-22 20:59 ` [PATCH 6/8] passt, util: Move opening of PID file to its own function Stefano Brivio
2024-05-23 10:06   ` Richard W.M. Jones
2024-05-28  7:04   ` David Gibson
2024-05-22 20:59 ` [PATCH 7/8] conf, passt, tap: Open socket and PID files before switching UID/GID Stefano Brivio
2024-05-23 10:10   ` Richard W.M. Jones
2024-05-29  2:35   ` David Gibson
2024-06-20 11:30     ` Richard W.M. Jones
2024-06-20 12:12       ` Stefano Brivio
2024-06-20 12:47         ` Richard W.M. Jones [this message]
2024-06-20 14:22           ` Stefano Brivio
2024-06-21  1:02             ` David Gibson
2024-05-22 20:59 ` [PATCH 8/8] conf, passt.h: Rename pid_file in struct ctx to pidfile Stefano Brivio
2024-05-23 10:11   ` Richard W.M. Jones
2024-05-28  7:07   ` David Gibson

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