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Date: Mon,  5 Jun 2017 05:47:55 +0200
From: "Jason A. Donenfeld" <Jason@...c4.com>
To: Theodore Ts'o <tytso@....edu>,
	Linux Crypto Mailing List <linux-crypto@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	kernel-hardening@...ts.openwall.com,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: "Jason A. Donenfeld" <Jason@...c4.com>,
	"Nicholas A. Bellinger" <nab@...ux-iscsi.org>,
	Lee Duncan <lduncan@...e.com>,
	Chris Leech <cleech@...hat.com>
Subject: [PATCH RFC v2 6/8] iscsi: ensure RNG is seeded before use

It's not safe to use weak random data here, especially for the challenge
response randomness. Since we're always in process context, it's safe to
simply wait until we have enough randomness to carry out the
authentication correctly.

While we're at it, we clean up a small memleak during an error
condition.

Signed-off-by: Jason A. Donenfeld <Jason@...c4.com>
Cc: "Nicholas A. Bellinger" <nab@...ux-iscsi.org>
Cc: Lee Duncan <lduncan@...e.com>
Cc: Chris Leech <cleech@...hat.com>
---
 drivers/target/iscsi/iscsi_target_auth.c  | 14 +++++++++++---
 drivers/target/iscsi/iscsi_target_login.c | 22 ++++++++++++++--------
 2 files changed, 25 insertions(+), 11 deletions(-)

diff --git a/drivers/target/iscsi/iscsi_target_auth.c b/drivers/target/iscsi/iscsi_target_auth.c
index 903b667f8e01..f9bc8ec6fb6b 100644
--- a/drivers/target/iscsi/iscsi_target_auth.c
+++ b/drivers/target/iscsi/iscsi_target_auth.c
@@ -47,18 +47,21 @@ static void chap_binaryhex_to_asciihex(char *dst, char *src, int src_len)
 	}
 }
 
-static void chap_gen_challenge(
+static int chap_gen_challenge(
 	struct iscsi_conn *conn,
 	int caller,
 	char *c_str,
 	unsigned int *c_len)
 {
+	int ret;
 	unsigned char challenge_asciihex[CHAP_CHALLENGE_LENGTH * 2 + 1];
 	struct iscsi_chap *chap = conn->auth_protocol;
 
 	memset(challenge_asciihex, 0, CHAP_CHALLENGE_LENGTH * 2 + 1);
 
-	get_random_bytes(chap->challenge, CHAP_CHALLENGE_LENGTH);
+	ret = get_random_bytes_wait(chap->challenge, CHAP_CHALLENGE_LENGTH);
+	if (unlikely(ret))
+		return ret;
 	chap_binaryhex_to_asciihex(challenge_asciihex, chap->challenge,
 				CHAP_CHALLENGE_LENGTH);
 	/*
@@ -69,6 +72,7 @@ static void chap_gen_challenge(
 
 	pr_debug("[%s] Sending CHAP_C=0x%s\n\n", (caller) ? "server" : "client",
 			challenge_asciihex);
+	return 0;
 }
 
 static int chap_check_algorithm(const char *a_str)
@@ -143,6 +147,7 @@ static struct iscsi_chap *chap_server_open(
 	case CHAP_DIGEST_UNKNOWN:
 	default:
 		pr_err("Unsupported CHAP_A value\n");
+		kfree(conn->auth_protocol);
 		return NULL;
 	}
 
@@ -156,7 +161,10 @@ static struct iscsi_chap *chap_server_open(
 	/*
 	 * Generate Challenge.
 	 */
-	chap_gen_challenge(conn, 1, aic_str, aic_len);
+	if (chap_gen_challenge(conn, 1, aic_str, aic_len) < 0) {
+		kfree(conn->auth_protocol);
+		return NULL;
+	}
 
 	return chap;
 }
diff --git a/drivers/target/iscsi/iscsi_target_login.c b/drivers/target/iscsi/iscsi_target_login.c
index 66238477137b..5ef028c11738 100644
--- a/drivers/target/iscsi/iscsi_target_login.c
+++ b/drivers/target/iscsi/iscsi_target_login.c
@@ -245,22 +245,26 @@ int iscsi_check_for_session_reinstatement(struct iscsi_conn *conn)
 	return 0;
 }
 
-static void iscsi_login_set_conn_values(
+static int iscsi_login_set_conn_values(
 	struct iscsi_session *sess,
 	struct iscsi_conn *conn,
 	__be16 cid)
 {
+	int ret;
 	conn->sess		= sess;
 	conn->cid		= be16_to_cpu(cid);
 	/*
 	 * Generate a random Status sequence number (statsn) for the new
 	 * iSCSI connection.
 	 */
-	get_random_bytes(&conn->stat_sn, sizeof(u32));
+	ret = get_random_bytes_wait(&conn->stat_sn, sizeof(u32));
+	if (unlikely(ret))
+		return ret;
 
 	mutex_lock(&auth_id_lock);
 	conn->auth_id		= iscsit_global->auth_id++;
 	mutex_unlock(&auth_id_lock);
+	return 0;
 }
 
 __printf(2, 3) int iscsi_change_param_sprintf(
@@ -306,7 +310,11 @@ static int iscsi_login_zero_tsih_s1(
 		return -ENOMEM;
 	}
 
-	iscsi_login_set_conn_values(sess, conn, pdu->cid);
+	ret = iscsi_login_set_conn_values(sess, conn, pdu->cid);
+	if (unlikely(ret)) {
+		kfree(sess);
+		return ret;
+	}
 	sess->init_task_tag	= pdu->itt;
 	memcpy(&sess->isid, pdu->isid, 6);
 	sess->exp_cmd_sn	= be32_to_cpu(pdu->cmdsn);
@@ -497,8 +505,7 @@ static int iscsi_login_non_zero_tsih_s1(
 {
 	struct iscsi_login_req *pdu = (struct iscsi_login_req *)buf;
 
-	iscsi_login_set_conn_values(NULL, conn, pdu->cid);
-	return 0;
+	return iscsi_login_set_conn_values(NULL, conn, pdu->cid);
 }
 
 /*
@@ -554,9 +561,8 @@ static int iscsi_login_non_zero_tsih_s2(
 		atomic_set(&sess->session_continuation, 1);
 	spin_unlock_bh(&sess->conn_lock);
 
-	iscsi_login_set_conn_values(sess, conn, pdu->cid);
-
-	if (iscsi_copy_param_list(&conn->param_list,
+	if (iscsi_login_set_conn_values(sess, conn, pdu->cid) < 0 ||
+	    iscsi_copy_param_list(&conn->param_list,
 			conn->tpg->param_list, 0) < 0) {
 		iscsit_tx_login_rsp(conn, ISCSI_STATUS_CLS_TARGET_ERR,
 				ISCSI_LOGIN_STATUS_NO_RESOURCES);
-- 
2.13.0

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