libata: don't try to pass through NCQ commands to non-NCQ devices

libata: don't try to pass through NCQ commands to non-NCQ devices

syzkaller hit a WARN() in ata_bmdma_qc_issue() when writing to /dev/sg0.
This happened because it issued an ATA pass-through command (ATA_16)
where the protocol field indicated that NCQ should be used -- but the
device did not support NCQ.

We could just remove the WARN() from libata-sff.c, but the real problem
seems to be that the SCSI -> ATA translation code passes through NCQ
commands without verifying that the device actually supports NCQ.

Fix this by adding the appropriate check to ata_scsi_pass_thru().

Here's reproducer that works in QEMU when /dev/sg0 refers to a disk of
the default type ("82371SB PIIX3 IDE"):

    #include <fcntl.h>
    #include <unistd.h>

    int main()
    {
            char buf[53] = { 0 };

	    buf[36] = 0x85;		/* ATA_16 */
	    buf[37] = (12 << 1);	/* FPDMA */
	    buf[38] = 0x1;		/* Has data */
	    buf[51] = 0xC8;		/* ATA_CMD_READ */
            write(open("/dev/sg0", O_RDWR), buf, sizeof(buf));
    }

Fixes: ee7fb331c3ac ("libata: add support for NCQ commands for SG interface")
Reported-by: syzbot+2f69ca28df61bdfc77cd36af2e789850355a221e@syzkaller.appspotmail.com
Cc: <stable@vger.kernel.org> # v4.4+
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Tejun Heo <tj@kernel.org>