iscsi-target: Reject mutual authentication with reflected CHAP_C

commit 1d2b60a5545942b1376cb48c1d55843d71e3a08f upstream.

This patch adds an explicit check in chap_server_compute_md5() to ensure
the CHAP_C value received from the initiator during mutual authentication
does not match the original CHAP_C provided by the target.

This is in line with RFC-3720, section 8.2.1:

   Originators MUST NOT reuse the CHAP challenge sent by the Responder
   for the other direction of a bidirectional authentication.
   Responders MUST check for this condition and close the iSCSI TCP
   connection if it occurs.

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

diff --git a/drivers/target/iscsi/iscsi_target_auth.c b/drivers/target/iscsi/iscsi_target_auth.c
index 59e7378..32eb6b4 100644 (file)
--- a/drivers/target/iscsi/iscsi_target_auth.c
+++ b/drivers/target/iscsi/iscsi_target_auth.c
@@ -336,6 +336,16 @@ static int chap_server_compute_md5(
                pr_err("Unable to convert incoming challenge\n");
                goto out;
        }
+       /*
+        * During mutual authentication, the CHAP_C generated by the
+        * initiator must not match the original CHAP_C generated by
+        * the target.
+        */
+       if (!memcmp(challenge_binhex, chap->challenge, CHAP_CHALLENGE_LENGTH)) {
+               pr_err("initiator CHAP_C matches target CHAP_C, failing"
+                      " login attempt\n");
+               goto out;
+       }
        /*
         * Generate CHAP_N and CHAP_R for mutual authentication.
         */