[PATCH v2] vhost-scsi: do not count PI bytes in the data length

[Jia Jia <physicalmtea@gmail.com>]

vhost_scsi_handle_vq() moves pi_bytesout or pi_bytesin into the
protection sgl and subtracts those bytes from exp_data_len.  The length
passed to TCM is still exp_data_len + prot_bytes.

prot_bytes comes from virtio_scsi_cmd_req_pi.  With
VIRTIO_SCSI_F_T10_PI negotiated, vhost reads that header and does not
check that the CDB is a READ or WRITE.  sbc_check_prot() replaces
data_length from the CDB only when the protect field is non-zero.
target_cmd_size_check() leaves a write's data_length unchanged when the
CDB size is smaller, so a command that does not get that replacement
keeps a data_length larger than the data sgl.

The KASAN report is a MODE SELECT whose header had pi_bytesout set.
The data sgl held only the parameter list.  spc_emulate_modeselect()
walked data_length and read the next physical page.

Pass the data sgl length.  Protected READ and WRITE still take their
length from the CDB in sbc_check_prot().

KASAN reports:

  BUG: KASAN: use-after-free in spc_emulate_modeselect+0x145/0x380 [target_core_mod]
  Read of size 1

  spc_emulate_modeselect
  __target_execute_cmd
  target_execute_cmd
  vhost_scsi_write_pending
  transport_generic_new_cmd
  __target_submit
  target_queued_submit_work
  process_one_work
  worker_thread
  kthread
  ret_from_fork
  ret_from_fork_asm

Fixes: 9f977ef7b671 ("vhost-scsi: Include prot_bytes into expected data transfer length")
Signed-off-by: Jia Jia <physicalmtea@gmail.com>
---
v2:
  - Drop the claim that target used to subtract prot_length.
    9f977ef7b671 cites 14ef9200, which is not in the tree
  - prot_bytes comes from virtio_scsi_cmd_req_pi

 drivers/vhost/scsi.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/drivers/vhost/scsi.c b/drivers/vhost/scsi.c
index 4f8c0260bc9e..4bd29c2ceed9 100644
--- a/drivers/vhost/scsi.c
+++ b/drivers/vhost/scsi.c
@@ -1534,9 +1534,13 @@ vhost_scsi_handle_vq(struct vhost_scsi *vs, struct vhost_virtqueue *vq)
 		 * vhost_scsi_queue_data_in() and vhost_scsi_queue_status()
 		 */
 		cmd->tvc_vq_desc = vc.head;
+		/*
+		 * exp_data_len is the data sgl. prot_bytes already sit in
+		 * the protection sgl. Protected READ and WRITE replace
+		 * data_length from the CDB in sbc_check_prot().
+		 */
 		vhost_scsi_target_queue_cmd(nexus, cmd, cdb, lun, task_attr,
-					    data_direction,
-					    exp_data_len + prot_bytes);
+					    data_direction, exp_data_len);
 		ret = 0;
 err:
 		/*
-- 
2.53.0