Date: Thu, 10 Dec 2009 09:32:08 +0000 (GMT) From: Robert Watson <rwatson@FreeBSD.org> To: xorquewasp@googlemail.com Cc: freebsd-hackers@freebsd.org Subject: Re: UNIX domain sockets on nullfs still broken? Message-ID: <alpine.BSF.2.00.0912100928200.23303@fledge.watson.org> In-Reply-To: <20091130142950.GA86528@logik.internal.network> References: <20091130142950.GA86528@logik.internal.network>
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On Mon, 30 Nov 2009, xorquewasp@googlemail.com wrote:
> jackd (audio/jack) creates a directory in /tmp with a UNIX domain socket in
> it. Clients connect to this socket to communicate with the server.
We currently support the sharing of UNIX domain sockets between file system
layers on either nullfs or unionfs. In the former case, this is a bug, and in
the latter case, it is a feature.
The specific nature of the bug is that you can't just copy the socket pointer
between layers in the vnode stack without additional reference counting (and
other similar state propagation), so if we allowed inter-layer access it would
lead to use-after-free panics and similar sorts of problems.
This occurs, BTW, because the socket pointer is directly in struct vnode, and
not queried by a VOP, which could be forwarded by nullfs down a layer. The
fixes here aren't easy, so I would anticipate UNIX domain sockets not working
across nullfs layers for some time to come. It's not immediately clear to me
which approach is the best way to fix it, since it likely requires UNIX domain
sockets to learn about stacked file systems in some form, which will
significantly complicate an already complicated relationship.
Robert N M Watson
Computer Laboratory
University of Cambridge
>
> $ jackd -d oss -r 44100 -p 128
> $ ls -alF /tmp/jack-11001/default
> total 4
> drwx------ 2 xw wheel 512 30 Nov 14:19 ./
> drwx------ 3 xw wheel 512 30 Nov 14:19 ../
> prw-r--r-- 1 xw wheel 0 30 Nov 14:19 jack-ack-fifo-54211-0|
> prw-r--r-- 1 xw wheel 0 30 Nov 14:19 jack-ack-fifo-54211-1|
> prw-r--r-- 1 xw wheel 0 30 Nov 14:19 jack-ack-fifo-54211-2|
> srwxr-xr-x 1 xw wheel 0 30 Nov 14:19 jack_0=
> srwxr-xr-x 1 xw wheel 0 30 Nov 14:19 jack_ack_0=
>
> $ sudo mount_nullfs /tmp/ /jail/k4m/tmp
>
> In the jail:
>
> k4m$ ls -alF /tmp/jack-11001/default
> drwx------ 2 xw wheel 512 30 Nov 14:19 ./
> drwx------ 3 xw wheel 512 30 Nov 14:19 ../
> prw-r--r-- 1 xw wheel 0 30 Nov 14:19 jack-ack-fifo-54211-0|
> prw-r--r-- 1 xw wheel 0 30 Nov 14:19 jack-ack-fifo-54211-1|
> prw-r--r-- 1 xw wheel 0 30 Nov 14:19 jack-ack-fifo-54211-2|
> srwxr-xr-x 1 xw wheel 0 30 Nov 14:19 jack_0=
> srwxr-xr-x 1 xw wheel 0 30 Nov 14:19 jack_ack_0=
>
> k4m$ ktrace jack_showtime
> jack server not running?
>
> k4m$ kdump | grep '/tmp/jack-11001'
> 76030 initial thread STRU struct sockaddr { AF_LOCAL, /tmp/jack-11001/default/jack_0 }
> 76030 initial thread NAMI "/tmp/jack-11001/default/jack_0"
> 76030 initial thread RET connect -1 errno 61 Connection refused
>
> $ uname -a
> FreeBSD viper.internal.network 8.0-RELEASE FreeBSD 8.0-RELEASE #0: Sat Nov 21 15:02:08 UTC 2009 root@mason.cse.buffalo.edu:/usr/obj/usr/src/sys/GENERIC amd64
>
> xw
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