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

[Tim Gardner]

On 12/07/2016 07:57 AM, Seth Forshee wrote:
> 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.
> 

I tried to adhere to the spirit of the upstream commit so that future
patches against this code won't have giant conflicts. As for
data_length, the comparison of (data_length > udev->data_size) ought to
be correct. I don't see how that could be an off by one error.

rtg
-- 
Tim Gardner tim.gardner at canonical.com