iscsi-target: Fix residual count hanlding + remove iscsi_cmd->residual_count

This patch fixes iscsi-target handling of underflow where residual data is
causing an OOPs by using the incorrect iscsi_cmd_t->data_length initially
assigned in iscsit_allocate_se_cmd().  It resets iscsi_cmd_t->data_length
from se_cmd_t->data_length after transport_generic_allocate_tasks()
has been invoked in iscsit_handle_scsi_cmd() RX context, and converts
iscsi_cmd->residual_count usage to access iscsi_cmd->se_cmd.residual_count
to get the proper residual count set by target-core.

Reported-by: <lists@internyc.net>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Andy Grover <agrover@redhat.com>
Cc: stable@kernel.org
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

2 files changed, 6 insertions, 5 deletions

diff --git a/drivers/target/iscsi/iscsi_target.c b/drivers/target/iscsi/iscsi_target.c
index 4d81e1007c92..26834eff8960 100644
--- a/drivers/target/iscsi/iscsi_target.c
+++ b/drivers/target/iscsi/iscsi_target.c
@@ -1039,6 +1039,8 @@ done:
                  */
                 send_check_condition = 1;
         } else {
+                cmd->data_length = cmd->se_cmd.data_length;
+
                 if (iscsit_decide_list_to_build(cmd, payload_length) < 0)
                         return iscsit_add_reject_from_cmd(
                                 ISCSI_REASON_BOOKMARK_NO_RESOURCES,
@@ -2508,10 +2510,10 @@ static int iscsit_send_data_in(
         if (hdr->flags & ISCSI_FLAG_DATA_STATUS) {
                 if (cmd->se_cmd.se_cmd_flags & SCF_OVERFLOW_BIT) {
                         hdr->flags |= ISCSI_FLAG_DATA_OVERFLOW;
-                        hdr->residual_count = cpu_to_be32(cmd->residual_count);
+                        hdr->residual_count = cpu_to_be32(cmd->se_cmd.residual_count);
                 } else if (cmd->se_cmd.se_cmd_flags & SCF_UNDERFLOW_BIT) {
                         hdr->flags |= ISCSI_FLAG_DATA_UNDERFLOW;
-                        hdr->residual_count = cpu_to_be32(cmd->residual_count);
+                        hdr->residual_count = cpu_to_be32(cmd->se_cmd.residual_count);
                 }
         }
         hton24(hdr->dlength, datain.length);
@@ -3013,10 +3015,10 @@ static int iscsit_send_status(
         hdr->flags              |= ISCSI_FLAG_CMD_FINAL;
         if (cmd->se_cmd.se_cmd_flags & SCF_OVERFLOW_BIT) {
                 hdr->flags |= ISCSI_FLAG_CMD_OVERFLOW;
-                hdr->residual_count = cpu_to_be32(cmd->residual_count);
+                hdr->residual_count = cpu_to_be32(cmd->se_cmd.residual_count);
         } else if (cmd->se_cmd.se_cmd_flags & SCF_UNDERFLOW_BIT) {
                 hdr->flags |= ISCSI_FLAG_CMD_UNDERFLOW;
-                hdr->residual_count = cpu_to_be32(cmd->residual_count);
+                hdr->residual_count = cpu_to_be32(cmd->se_cmd.residual_count);
         }
         hdr->response           = cmd->iscsi_response;
         hdr->cmd_status         = cmd->se_cmd.scsi_status;
diff --git a/drivers/target/iscsi/iscsi_target_core.h b/drivers/target/iscsi/iscsi_target_core.h
index 3723d90d5ae5..0e96a6b13174 100644
--- a/drivers/target/iscsi/iscsi_target_core.h
+++ b/drivers/target/iscsi/iscsi_target_core.h
@@ -398,7 +398,6 @@ struct iscsi_cmd {
         u32                     pdu_send_order;
         /* Current struct iscsi_pdu in struct iscsi_cmd->pdu_list */
         u32                     pdu_start;
-        u32                     residual_count;
         /* Next struct iscsi_seq to send in struct iscsi_cmd->seq_list */
         u32                     seq_send_order;
         /* Number of struct iscsi_seq in struct iscsi_cmd->seq_list */