On Sun, Oct 11, 2026 at 09:48:03AM +0800, Jia Jia wrote:
> 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 <[email protected]>
> ---
> 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
you can mention the other patches you sent fixing
security maybe this will calm down sashiko.
>
> 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().
this is barely readable - could you improve pls? even if that makes it
a bit more verbose.
> + */
> 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
