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  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]
Date:	Wed, 3 Feb 2016 12:56:22 +0100
From:	Hannes Frederic Sowa <>
To:	Simon McVittie <>,
	David Herrmann <>,
	Willy Tarreau <>
Cc:	"David S. Miller" <>,
	netdev <>,
	linux-kernel <>,
	Linus Torvalds <>,
	Eric Dumazet <>,,
	Tetsuo Handa <>
Subject: Re: [PATCH v2] unix: properly account for FDs passed over unix

On 03.02.2016 12:36, Simon McVittie wrote:
> On 02/02/16 17:34, David Herrmann wrote:
>> Furthermore, with this patch in place, a process better not pass any
>> file-descriptors to an untrusted process.
> ...
>> Did anyone notify the dbus maintainers of this? They
>> might wanna document this, if not already done (CC: smcv).
> Sorry, I'm not clear from this message on what patterns I should be
> documenting as bad, and what the effect of non-compliance would be.
> dbus-daemon has a fd-passing feature, which uses AF_UNIX sockets'
> existing ability to pass fds to let users of D-Bus attach fds to their
> messages. The message is passed from the sending client to dbus-daemon,
> then from dbus-daemon to the recipient:
>               AF_UNIX             AF_UNIX
>                 |                    |
>      sender -------> dbus-daemon -------> recipient
>                 |                    |
> This has been API since before I was a D-Bus maintainer, so I have no
> influence over its existence; just like the kernel doesn't want to break
> user-space, dbus-daemon doesn't want to break its users.
> The system dbus-daemon (dbus-daemon --system) is a privilege boundary,
> and accepts senders and recipients with differing privileges. Without
> configuration, messages are denied by default. Recipients can open this
> up (by installing system-wide configuration) to allow arbitrary
> processes to send messages to them, so that they can carry out their own
> discretionary access control. Since 2014, the system dbus-daemon accepts
> up to 16 file descriptors per message by default.
> There is also a session or user dbus-daemon (dbus-daemon --session) per
> uid, but that isn't normally a privilege boundary, so any user trying to
> carry out a denial of service there is only hurting themselves.
> Am I right in saying that the advice I give to D-Bus users should be
> something like this?
> * system services should not send fds at all, unless they trust the
>    dbus-daemon
> * system services should not send fds via D-Bus that will be delivered
>    to recipients that they do not trust
> * sending fds to an untrusted recipient would enable that recipient to
>    carry out a denial-of-service attack (on what? the sender? the
>    dbus-daemon?)

The described behavior was simply a bug in the referenced patch. I 
already posted a follow-up to change this behavior so that only the 
current sending process is credited with the number of fds in flight:


Other processes (in this case the original opener of the file) isn't 
credited anymore if it does not send the fd itself.

That said, I don't think you need to change anything or give different 
advice because of this thread.


Powered by blists - more mailing lists