Re: SG_IO and security

[Bill Davidsen <davidsen@tmr.com>]

Linus Torvalds wrote:
> 
> On Thu, 12 Aug 2004, Jeff Garzik wrote:
> 
>>Linus Torvalds wrote:
>>
>>>On Thu, 12 Aug 2004, Linus Torvalds wrote:
>>>
>>>
>>>>Hmm.. This still allows the old "junk" commands (SCSI_IOCTL_SEND_COMMAND).
>>>
>>>
>>>Btw, I think the _right_ thing to check is the write access of the file 
>>>descriptor. If you have write access to a block device, you can delete the 
>>>data, so you might as well be able to do the raw commands. And that would 
>>>allow things like "disk" groups etc to work and burn CD's.
>>
>>Define raw commands.  I certainly don't want non-root users to be able 
>>to issue FORMAT UNIT on my hard drive.
> 
> 
> Ehh? The same ones you allow to write all over the raw device?
> 
> Let's see now:
> 
> 	brw-rw----    1 root     disk       3,   0 Jan 30  2003 /dev/hda
> 
> would you put people you don't trust with your disk in the "disk" group?
> 
> Right. If you trust somebody enough that you give him write access to the 
> disk, then you might as well trust him enough to do commands on it. 
> 
> Conversely, if you don't trust him enough to do things like that, you 
> shouldn't give him write access in the first place.
> 
> It's a hell of a lot easier to destroy a disk with
> 
> 	dd if=/dev/zero of=/dev/xxx bs=8k
> 
> than it is to do it with some special malicious command. 
> 
> And yes, there's clearly a difference, but in general I'd say it is the 
> _data_ on the disk that is worth something to you. The disk itself? Do you 
> really fundamentally care?

I will offer two cases which is not wildly improbable. User complains 
the CD burner will {burn faster, burn brand X media, write HD mode} if 
the firmware is upgraded. User has write to burn CDs, decides to flash 
the firmware herself, turns CD into paperweight. Or possibly user tries 
to install CD firmware on a disk drive.

Case two, user is DBA, has write on raw partitions for Oracle, can 
mangle the whole device, and through some stupidity does.

-- 
    -bill davidsen (davidsen@tmr.com)
"The secret to procrastination is to put things off until the
  last possible moment - but no longer"  -me