Re: [REGRESSION] 28676d869bbb (scsi: sg: check for valid direction before starting the request) breaks mtx tape library control

[Johannes Thumshirn]

On Tue, Jul 25, 2017 at 01:25:07PM -0500, Jason L Tibbitts III wrote:
> >>>>> "JT" == Johannes Thumshirn <jthumsh...@suse.de> writes:
> ioctl(3, SG_IO, {interface_id='S', dxfer_direction=SG_DXFER_TO_DEV, 
> cmd_len=12, cmdp="\xa5\x00\x00\x00\x00\x01\x03\xe9\x00\x00\x00\x00", 
> mx_sb_len=20, iovec_count=0, dxfer_len=0, timeout=300000, flags=0, 
> dxferp=NULL, status=0, masked_status=0, msg_status=0, sb_len_wr=0, sbp="", 
> host_status=0, driver_status=0, resid=0, duration=0, info=0}) = -1 EINVAL 
> (Invalid argument)

[...]
        case SG_DXFER_TO_DEV:
        case SG_DXFER_TO_FROM_DEV:
                if (!hp->dxferp)
                        return false;
                return true;

So here we go, dxfer_direction is SG_DXFER_TO_DEV, dxfer_len is 0 and dxferp
is NULL. We bail out because dxferp is NULL here.

I only looked at sg_write() and not sg_new_write() which is called by the
SG_IO path not the fops->write() path.

It's probably best to just check for dxfer_len <= 2^28 to be valid as Doug
suggested:

diff --git a/drivers/scsi/sg.c b/drivers/scsi/sg.c
index 4fe606b000b4..d7ff71e0c85c 100644
--- a/drivers/scsi/sg.c
+++ b/drivers/scsi/sg.c
@@ -751,35 +751,6 @@ sg_new_write(Sg_fd *sfp, struct file *file, const char 
__user *buf,
        return count;
 }
 
-static bool sg_is_valid_dxfer(sg_io_hdr_t *hp)
-{
-       switch (hp->dxfer_direction) {
-       case SG_DXFER_NONE:
-               if (hp->dxferp || hp->dxfer_len > 0)
-                       return false;
-               return true;
-       case SG_DXFER_FROM_DEV:
-               /*
-                * for SG_DXFER_FROM_DEV we always set dxfer_len to > 0. dxferp
-                * can either be NULL or != NULL so there's no point in checking
-                * it either. So just return true.
-                */
-               return true;
-       case SG_DXFER_TO_DEV:
-       case SG_DXFER_TO_FROM_DEV:
-               if (!hp->dxferp || hp->dxfer_len == 0)
-                       return false;
-               return true;
-       case SG_DXFER_UNKNOWN:
-               if ((!hp->dxferp && hp->dxfer_len) ||
-                   (hp->dxferp && hp->dxfer_len == 0))
-                       return false;
-               return true;
-       default:
-               return false;
-       }
-}
-
 static int
 sg_common_write(Sg_fd * sfp, Sg_request * srp,
                unsigned char *cmnd, int timeout, int blocking)
@@ -800,7 +771,7 @@ sg_common_write(Sg_fd * sfp, Sg_request * srp,
                        "sg_common_write:  scsi opcode=0x%02x, cmd_size=%d\n",
                        (int) cmnd[0], (int) hp->cmd_len));
 
-       if (!sg_is_valid_dxfer(hp))
+       if (hp->dxfer_len >= SZ_256M)
                return -EINVAL;
 
        k = sg_start_req(srp, cmnd);

-- 
Johannes Thumshirn                                          Storage
jthumsh...@suse.de                                +49 911 74053 689
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