[pulseaudio-discuss] system-wide daemon

[Colin Guthrie]

'Twas brillig, and Markus Rechberger at 10/02/10 08:59 did gyre and gimble:
> On Wed, Feb 10, 2010 at 9:54 AM, Colin Guthrie <gmane at colin.guthr.ie> wrote:
>>> Here's another analogy; what about the printer? If printers were
>>> considered a part of the seat, then user Bar wouldn't have more right to
>>> print a document either. (The corresponding spy-on-mic analogy would be
>>> that someone puts a document in a scanner and another user scans it...)
>>>
>>> But printers are more of a system-wide resource, and for some use cases,
>>> so is the soundcard. And then, sharing makes sense. If another user is
>>> allowed to print a document while I'm logged in, why shouldn't he be
>>> able to play a sound? So would then the solution be to run PA as a
>>> system-wide daemon, and possibly assign soundcards to it via udev?
>>
>> It's a fair enough point, but I don't think that sound and printers are
>> so alike. Even the scanner example AFAIK would fall under the current PA
>> setup - I believe that sane accesses them on a per-user basis with
>> appropriate ACLs on the device..
>>
>> /me checks....
>>
>> [colin at jimmy ~]$ su test
>> Password:
>> [test at jimmy colin]$ scanimage -L
>> libusb couldn't open USB device /dev/bus/usb/005/011: Permission denied.
>> libusb requires write access to USB device nodes.
>>
> 
> this is another wrong assumption, libusb uses raw USB access, if every
> user would have access
> to USB some devices might be damaged.
> Sane would need to be serverbased, full raw access to the usb bus
> would seriously be a security
> risk (imagine RAW USB access to a USB harddisk).

I fail to see where my assumption is here.

Console-Kit has applied appropriate ACLs to the device node. That was my
point and it was correct. No assumption stated nor needed as to what
happens further down the stack.

[test at jimmy colin]$ getfacl /dev/bus/usb/005/011
getfacl: Removing leading '/' from absolute path names
# file: dev/bus/usb/005/011
# owner: root
# group: root
user::rw-
user:colin:rw-
group::rw-
mask::rw-
other::r--


The same is true of audio devices. What if multiple users were allowed
direct access. Someone may design a security system with an alarm driven
from the sound system but some other user has come in and hogged the
device and as it does not support hardware mixing the "nuclear reactor
meltdown in 5mins" alarm does not sound and we all die a horrible firey
death. That's worse than a HD failure :p


Col


-- 

Colin Guthrie
gmane(at)colin.guthr.ie
http://colin.guthr.ie/

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