iscsi-target: Fix CHAP_A parameter list handling

The target is failing to handle list of CHAP_A key-value pair form
initiator.The target is expecting CHAP_A=5 always. In other cases,
where initiator sends list (for example) CHAP_A=6,5 target is failing
the security negotiation. Which is incorrect.

This patch handles the case (RFC 3720 section 11.1.4).
where in the initiator may send list of CHAP_A values and target replies
with appropriate CHAP_A value in response

(Drop whitespaces + rename to chap_check_algorithm + save original
 pointer + add explicit check for CHAP_A key - nab)

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

drivers/target/iscsi/iscsi_target_auth.c

@@ -71,6 +71,40 @@ static void chap_gen_challenge(
 			challenge_asciihex);
 }
 
+static int chap_check_algorithm(const char *a_str)
+{
+	char *tmp, *orig, *token;
+
+	tmp = kstrdup(a_str, GFP_KERNEL);
+	if (!tmp) {
+		pr_err("Memory allocation failed for CHAP_A temporary buffer\n");
+		return CHAP_DIGEST_UNKNOWN;
+	}
+	orig = tmp;
+
+	token = strsep(&tmp, "=");
+	if (!token)
+		goto out;
+
+	if (strcmp(token, "CHAP_A")) {
+		pr_err("Unable to locate CHAP_A key\n");
+		goto out;
+	}
+	while (token) {
+		token = strsep(&tmp, ",");
+		if (!token)
+			goto out;
+
+		if (!strncmp(token, "5", 1)) {
+			pr_debug("Selected MD5 Algorithm\n");
+			kfree(orig);
+			return CHAP_DIGEST_MD5;
+		}
+	}
+out:
+	kfree(orig);
+	return CHAP_DIGEST_UNKNOWN;
+}
 
 static struct iscsi_chap *chap_server_open(
 	struct iscsi_conn *conn,
@@ -79,6 +113,7 @@ static struct iscsi_chap *chap_server_open(
 	char *aic_str,
 	unsigned int *aic_len)
 {
+	int ret;
 	struct iscsi_chap *chap;
 
 	if (!(auth->naf_flags & NAF_USERID_SET) ||
@@ -93,21 +128,24 @@ static struct iscsi_chap *chap_server_open(
 		return NULL;
 
 	chap = conn->auth_protocol;
-	/*
-	 * We only support MD5 MDA presently.
-	 */
-	if (strncmp(a_str, "CHAP_A=5", 8)) {
-		pr_err("CHAP_A is not MD5.\n");
+	ret = chap_check_algorithm(a_str);
+	switch (ret) {
+	case CHAP_DIGEST_MD5:
+		pr_debug("[server] Got CHAP_A=5\n");
+		/*
+		 * Send back CHAP_A set to MD5.
+		*/
+		*aic_len = sprintf(aic_str, "CHAP_A=5");
+		*aic_len += 1;
+		chap->digest_type = CHAP_DIGEST_MD5;
+		pr_debug("[server] Sending CHAP_A=%d\n", chap->digest_type);
+		break;
+	case CHAP_DIGEST_UNKNOWN:
+	default:
+		pr_err("Unsupported CHAP_A value\n");
 		return NULL;
 	}
-	pr_debug("[server] Got CHAP_A=5\n");
-	/*
-	 * Send back CHAP_A set to MD5.
-	 */
-	*aic_len = sprintf(aic_str, "CHAP_A=5");
-	*aic_len += 1;
-	chap->digest_type = CHAP_DIGEST_MD5;
-	pr_debug("[server] Sending CHAP_A=%d\n", chap->digest_type);
+
 	/*
 	 * Set Identifier.
 	 */

drivers/target/iscsi/iscsi_target_auth.h

@@ -1,6 +1,7 @@
 #ifndef _ISCSI_CHAP_H_
 #define _ISCSI_CHAP_H_
 
+#define CHAP_DIGEST_UNKNOWN	0
 #define CHAP_DIGEST_MD5		5
 #define CHAP_DIGEST_SHA		6