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    SubjectRe: SG_IO and security
    Date
    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
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