iscsi-target: Reject zero-length payloads during SecurityNegotiation

This patch changes iscsi_target_handle_csg_zero() to explicitly
reject login requests in SecurityNegotiation with a zero-length
payload, following the language in RFC-3720 Section 8.2:

  Whenever an iSCSI target gets a response whose keys, or their
  values, are not according to the step definition, it MUST answer
  with a Login reject with the "Initiator Error" or "Missing Parameter"
  status.

Previously when a zero-length login request in CSG=0 was received,
the target would send a login response with CSG=0 + T_BIT=0 asking
the initiator to complete authentication, and not fail the login
until MAX_LOGIN_PDUS was reached.  This change will now immediately
fail the login attempt with ISCSI_STATUS_CLS_INITIATOR_ERR status.

Reported-by: Tejas Vaykole <tejas.vaykole@calsoftinc.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

1 files changed, 6 insertions, 0 deletions

diff --git a/drivers/target/iscsi/iscsi_target_nego.c b/drivers/target/iscsi/iscsi_target_nego.c
index 75b685960e80..fcffd0412d83 100644
--- a/drivers/target/iscsi/iscsi_target_nego.c
+++ b/drivers/target/iscsi/iscsi_target_nego.c
@@ -773,6 +773,12 @@ static int iscsi_target_handle_csg_zero(
                 }
 
                 goto do_auth;
+        } else if (!payload_length) {
+                pr_err("Initiator sent zero length security payload,"
+                       " login failed\n");
+                iscsit_tx_login_rsp(conn, ISCSI_STATUS_CLS_INITIATOR_ERR,
+                                    ISCSI_LOGIN_STATUS_AUTH_FAILED);
+                return -1;
         }
 
         if (login->first_request)