[PATCH 2/4] target/user: Return an error if cmd data size is too large

[Seth Forshee]

On Tue, Dec 06, 2016 at 12:40:53PM -0700, Tim Gardner wrote:
> From: Andy Grover <agrover at redhat.com>
> 
> BugLink: http://bugs.launchpad.net/bugs/1646204
> 
> Userspace should be implementing VPD B0 (Block Limits) to inform the
> initiator of max data size, but just in case we do get a too-large request,
> do what the spec says and return INVALID_CDB_FIELD.
> 
> Make sure to unlock udev->cmdr_lock before returning.
> 
> Signed-off-by: Andy Grover <agrover at redhat.com>
> Reviewed-by: Christoph Hellwig <hch at lst.de>
> Reviewed-by: Mike Christie <mchristi at redhat.com>
> Signed-off-by: Nicholas Bellinger <nab at linux-iscsi.org>
> (back ported from commit 554617b2bbe25c3fb3c80c28fe7a465884bb40b1)
> Signed-off-by: Tim Gardner <tim.gardner at canonical.com>
> 
> Conflicts:
> 	drivers/target/target_core_user.c
> ---
>  drivers/target/target_core_user.c | 17 +++++++++++++----
>  1 file changed, 13 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/target/target_core_user.c b/drivers/target/target_core_user.c
> index 28debdf..c252528 100644
> --- a/drivers/target/target_core_user.c
> +++ b/drivers/target/target_core_user.c
> @@ -393,6 +393,7 @@ tcmu_queue_cmd_ring(struct tcmu_cmd *tcmu_cmd)
>  	uint32_t cmd_head;
>  	uint64_t cdb_off;
>  	bool copy_to_data_area;
> +	size_t data_length;
>  
>  	if (test_bit(TCMU_DEV_BIT_BROKEN, &udev->flags))
>  		return TCM_LOGICAL_UNIT_COMMUNICATION_FAILURE;
> @@ -417,11 +418,19 @@ tcmu_queue_cmd_ring(struct tcmu_cmd *tcmu_cmd)
>  
>  	mb = udev->mb_addr;
>  	cmd_head = mb->cmd_head % udev->cmdr_size; /* UAM */
> -	if ((command_size > (udev->cmdr_size / 2))
> -	    || tcmu_cmd->data_length > (udev->data_size - 1))
> -		pr_warn("TCMU: Request of size %zu/%zu may be too big for %u/%zu "
> -			"cmd/data ring buffers\n", command_size, tcmu_cmd->data_length,
> +	data_length = se_cmd->data_length;
> +	if (se_cmd->se_cmd_flags & SCF_BIDI) {
> +		BUG_ON(!(se_cmd->t_bidi_data_sg && se_cmd->t_bidi_data_nents));
> +		data_length += se_cmd->t_bidi_data_sg->length;
> +	}

This really backports more changes than are necessary. This part
duplicates code in tcmu_alloc_cmd(), which was moved here by
26418649eead "target/user: Introduce data_bitmap, replace
data_length/data_head/data_tail" because the data_length member of
tcmu_cmd was removed.

> +	if ((command_size > (udev->cmdr_size / 2)) ||
> +	    data_length > udev->data_size) {
> +		pr_warn("TCMU: Request of size %zu/%zu is too big for %u/%zu "
> +			"cmd/data ring buffers\n", command_size, data_length,
>  			udev->cmdr_size, udev->data_size);
> +		spin_unlock_irq(&udev->cmdr_lock);
> +		return TCM_INVALID_CDB_FIELD;
> +	}

And so this part should be able to continue using tcmu_cmd->data_length
as before. All that's really needed is to change this chunk to look like
this:

        if ((command_size > (udev->cmdr_size / 2)) ||
            tcmu_cmd->data_length > (udev->data_size - 1)) {
                pr_warn("TCMU: Request of size %zu/%zu may be too big for %u/%zu "
                        "cmd/data ring buffers\n", command_size, tcmu_cmd->data_length,
                        udev->cmdr_size, udev->data_size);
                spin_unlock_irq(&udev->cmdr_lock);
                return TCM_INVALID_CDB_FIELD;
        }

(I'm not sure about the (udev->data_size - 1) -> udev->data_size part,
was also changed in 26418649eead without explanation so maybe an
off-by-one error.)

I don't think your backport actually breaks anything though, it just
backports more than is necessary.