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    SubjectRe: [PATCH] drivers/block/scsi_ioctl.c, Video DVD playback support
    On Mon, Jan 24 2005, Elias da Silva wrote:
    > > On Sat, Jan 22 2005, Elias da Silva wrote:
    > > > Attached patch fixes a problem of reading Video DVDs
    > > > through the cdrom_ioctl interface. VMware is among
    > > > the prominent victims.
    > > >
    > > > The bug was introduced in kernel version 2.6.8 in the
    > > > function verify_command().
    > >
    > > It's not a bug, add write permission to the device for the user using
    > > the drive.
    > Hi.
    >
    > The device already has write permission for the user using the
    > drive... and this is not the point.
    >
    > The point is
    > a. the user (program) wants to read a protected DVD,
    >
    > b. the user has permission to read the device,
    >
    > c. since kernel 2.6.8 the user can't use his right to read a
    > DVD media, because according to verify_command() he is forced
    > to open the device with RW mode instead of RONLY.

    Right, it's an unfortunate side effect of the command table.

    > This is true for protected media because of the authentication
    > process needed between "host" and DVD device. IMHO,
    > the classification of the opcodes
    >
    > a. GPCMD_SEND_KEY and
    > b. GPCMD_SET_STREAMING
    >
    > as only "save for write" is wrong.

    You need to explain why you think that is so, since this is the core of
    the argument. The only thing I can say is that perhaps SEND_KEY should
    even be root only, since it has a fairly large scope. It's really a
    device exclusive type situation, where is a user has exclusive access to
    the device it would be ok to issue a SEND_KEY but otherwise not. It's
    not clearly a read vs write thing. It's impossible to shoe-horn a more
    complicated permission model on top of something as silly as read vs
    write.

    > Furthermore, if you use
    > a. cdrom_ioctl (..., DVD_AUTH,...) instead of
    > b. cdrom_ioctl (..., CDROM_SEND_PACKET,...)
    > -> scsi_cmd_ioctl()-> sg_io()-> verify_command()
    >
    > the same authentication procedure works as expected on a
    > RONLY opened device!

    DVD_AUTH by-passes scsi_ioctl.c, so yes.

    > Please rethink your decisions introduced with verify_command()
    > and make for example VMware work _again_ with Video DVDs.

    It's not my decisions. The problem is that it is policy, and it has to
    be restrictive to be safe.

    --
    Jens Axboe

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