iscsi-target: Reject mutual authentication with reflected CHAP_C

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>
Cc: stable@vger.kernel.org # 3.1+
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

1 files changed, 10 insertions, 0 deletions

diff --git a/drivers/target/iscsi/iscsi_target_auth.c b/drivers/target/iscsi/iscsi_target_auth.c
index 155f33848aa6..19b842c3e0b3 100644
--- a/drivers/target/iscsi/iscsi_target_auth.c
+++ b/drivers/target/iscsi/iscsi_target_auth.c
@@ -352,6 +352,16 @@ static int chap_server_compute_md5(
                 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.
          */
         tfm = crypto_alloc_hash("md5", 0, CRYPTO_ALG_ASYNC);