Re: Linux 2.6.8.1 requires changes to cdrecord (and probably every other CD/DVD writing app)
On Mon, Aug 16, 2004 at 05:38:36PM +0200, Joerg Schilling wrote:
>From: Andreas Metzler <ametzler@logic.univie.ac.at>
> ><http://marc.theaimsgroup.com/?t=109260648900001&r=1&w=2>? Writing CDs
> >only works *as* root, SUID root is not enough. - I've been told that
[...]
> http://marc.theaimsgroup.com/?l=linux-kernel&m=109264207926099&w=2
> makes me believe that Linux-2.6.8 does not allow the MODE SENDE and/or
> MODE SELECT command.
Disclaimer: I have not looked at any code.
> If this is true, then somenone in the Linux Kernel group need to get
> fired :-( If there really is a differende between EUID root and UID
> root, then they did not understand the POSIX security model: Rights
> are checked against EUID and in case of a suid cdrecord, EUID is
> root.
I do not think that is the case, because it would break _lots_
of stuff, the problem seems to be that cdrecord drops privileges it
needs to access the hardware.
> However, in case that they tried to implement similar security
> enhancements as Sun did starting with Solaris 9, then libscg would
> need the same modification as it needed on Solaris (switching
> to/from root bracheting each SCSI command).
That sounds much more probable.
> (On Solaris 9 you need to have EUID root while you send a SCSI
> command via USCSI).
> I am sorry, but as this would not be a bug fix cdrtools, it is too
> late to make it into cdrtools-2.01-final.
I am not going to try to set release goals for you.
>> Cdrecord needs to keep CAP_SYS_RAWIO.
> Could you explain this? It is not mentioned in the list if mails you send.
Linux(iirc since 2.2) supports a finer grained permission model than
switching UID, POSIX capabilities[1]. Instead of "switching to/from
root bracketing each SCSI command" you'd simply retain the necessary
capability, CAP_SYS_RAWIO.
cu andreas
[1] It is not part of IEEE Std 1003.1. I gather from
http://wt.xpilot.org/publications/posix.1e/ that the gremium has given
up on standardizing it.
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