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SubjectRe: SG_IO and security
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 (
"The secret to procrastination is to put things off until the
last possible moment - but no longer" -me
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