UNIX domain sockets on nullfs still broken?

[Robert Watson]

On Mon, 30 Nov 2009, xorquewasp at 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 at mason.cse.buffalo.edu:/usr/obj/usr/src/sys/GENERIC  amd64
>
> xw
> _______________________________________________
> freebsd-hackers at freebsd.org mailing list
> http://lists.freebsd.org/mailman/listinfo/freebsd-hackers
> To unsubscribe, send any mail to "freebsd-hackers-unsubscribe at freebsd.org"
>