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    SubjectRe: Re: [GIT PULL] SCSI fixes for 4.18-rc3
    On Tue, Jul 10, 2018 at 2:53 PM Tony Battersby <tonyb@cybernetics.com> wrote:
    >
    > At my job (https://www.cybernetics.com/), I use the write()/read()
    > interface to the SCSI generic driver for access to tape drives and tape
    > medium changers. For example, the write()/read() interface is useful
    > for implementing RAID-like functionality for tape drives since a single
    > thread can send commands to multiple tape drives at once and poll() for
    > command completion.

    Ugh.

    > We have a lot of code invested in this interface,
    > so it would be a huge pain for us if it were removed. But in our case,
    > everything runs as root (as the firmware of an embedded storage
    > appliance), so extra permission checks should be OK.

    I wonder if we could make the warning literally about not having
    CAP_SYS_RAWIO on the file descriptor.

    Because the /dev/sg interfaces don't even do the kind of command
    filtering that the SG_IO code does.

    The SG_IO code (well, at least the block/scsi_ioctl.c code - again
    /dev/sg does NOT get it right!) actually has a whitelist of commands
    that have known behavior, and that can be done by normal users when
    you open a device.

    To actually do _arbitrary_ commands, you have to have CAP_SYS_RAWIO.
    And there we check the _current_ capabilities (not the file descriptor
    one), because an ioctl isn't something you just fool a random suid
    program into doing for you.

    So /dev/sg really has serious issues. Not just the read/write part,
    but even the SG_IO part is broken right now (sg_new_write() actually
    does do blk_verify_command(), but only for read-only opens for some
    reason).

    Linus

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