target: Fix ->data_length re-assignment bug with SCSI overflow

commit 4c054ba63ad47ef244cfcfa1cea38134620a5bae upstream.

This patch fixes a long-standing bug with SCSI overflow handling
where se_cmd->data_length was incorrectly being re-assigned to
the larger CDB extracted allocation length, resulting in a number
of fabric level errors that would end up causing a session reset
in most cases.  So instead now:

 - Only re-assign se_cmd->data_length durining UNDERFLOW (to use the
   smaller value)
 - Use existing se_cmd->data_length for OVERFLOW (to use the smaller
   value)

This fix has been tested with the following CDB to generate an
SCSI overflow:

  sg_raw -r512 /dev/sdc 28 0 0 0 0 0 0 0 9 0

Tested using iscsi-target, tcm_qla2xxx, loopback and tcm_vhost fabric
ports.  Here is a bit more detail on each case:

 - iscsi-target: Bug with open-iscsi with overflow, sg_raw returns
                 -3584 bytes of data.
 - tcm_qla2xxx: Working as expected, returnins 512 bytes of data
 - loopback: sg_raw returns CHECK_CONDITION, from overflow rejection
             in transport_generic_map_mem_to_cmd()
 - tcm_vhost: Same as loopback

Reported-by: Roland Dreier <roland@purestorage.com>
Cc: Roland Dreier <roland@purestorage.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Boaz Harrosh <bharrosh@panasas.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --git a/drivers/target/target_core_transport.c b/drivers/target/target_core_transport.c
index 597fb9b..34d114a 100644 (file)
--- a/drivers/target/target_core_transport.c
+++ b/drivers/target/target_core_transport.c
@@ -3039,15 +3039,20 @@ static int transport_generic_cmd_sequencer(
                        /* Returns CHECK_CONDITION + INVALID_CDB_FIELD */
                        goto out_invalid_cdb_field;
                }
-
+               /*
+                * For the overflow case keep the existing fabric provided
+                * ->data_length.  Otherwise for the underflow case, reset
+                * ->data_length to the smaller SCSI expected data transfer
+                * length.
+                */
                if (size > cmd->data_length) {
                        cmd->se_cmd_flags |= SCF_OVERFLOW_BIT;
                        cmd->residual_count = (size - cmd->data_length);
                } else {
                        cmd->se_cmd_flags |= SCF_UNDERFLOW_BIT;
                        cmd->residual_count = (cmd->data_length - size);
+                       cmd->data_length = size;
                }
-               cmd->data_length = size;
        }
 
        /* reject any command that we don't have a handler for */