net/tls: Fixed race condition in async encryption

On processors with multi-engine crypto accelerators, it is possible that
multiple records get encrypted in parallel and their encryption
completion is notified to different cpus in multicore processor. This
leads to the situation where tls_encrypt_done() starts executing in
parallel on different cores. In current implementation, encrypted
records are queued to tx_ready_list in tls_encrypt_done(). This requires
addition to linked list 'tx_ready_list' to be protected. As
tls_decrypt_done() could be executing in irq content, it is not possible
to protect linked list addition operation using a lock.

To fix the problem, we remove linked list addition operation from the
irq context. We do tx_ready_list addition/removal operation from
application context only and get rid of possible multiple access to
the linked list. Before starting encryption on the record, we add it to
the tail of tx_ready_list. To prevent tls_tx_records() from transmitting
it, we mark the record with a new flag 'tx_ready' in 'struct tls_rec'.
When record encryption gets completed, tls_encrypt_done() has to only
update the 'tx_ready' flag to true & linked list add operation is not
required.

The changed logic brings some other side benefits. Since the records
are always submitted in tls sequence number order for encryption, the
tx_ready_list always remains sorted and addition of new records to it
does not have to traverse the linked list.

Lastly, we renamed tx_ready_list in 'struct tls_sw_context_tx' to
'tx_list'. This is because now, the some of the records at the tail are
not ready to transmit.

Fixes: a42055e8d2c3 ("net/tls: Add support for async encryption")
Signed-off-by: Vakul Garg <vakul.garg@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/tls.h

@@ -99,6 +99,7 @@ enum {
  */
 struct tls_rec {
 	struct list_head list;
+	int tx_ready;
 	int tx_flags;
 	struct scatterlist sg_plaintext_data[MAX_SKB_FRAGS];
 	struct scatterlist sg_encrypted_data[MAX_SKB_FRAGS];
@@ -128,7 +129,7 @@ struct tls_sw_context_tx {
 	struct crypto_wait async_wait;
 	struct tx_work tx_work;
 	struct tls_rec *open_rec;
-	struct list_head tx_ready_list;
+	struct list_head tx_list;
 	atomic_t encrypt_pending;
 	int async_notify;
 
@@ -220,7 +221,6 @@ struct tls_context {
 
 	struct scatterlist *partially_sent_record;
 	u16 partially_sent_offset;
-	u64 tx_seq_number;	/* Next TLS seqnum to be transmitted */
 
 	unsigned long flags;
 	bool in_tcp_sendpages;
@@ -341,21 +341,15 @@ static inline bool tls_is_pending_open_record(struct tls_context *tls_ctx)
 	return tls_ctx->pending_open_record_frags;
 }
 
-static inline bool is_tx_ready(struct tls_context *tls_ctx,
-			       struct tls_sw_context_tx *ctx)
+static inline bool is_tx_ready(struct tls_sw_context_tx *ctx)
 {
 	struct tls_rec *rec;
-	u64 seq;
 
-	rec = list_first_entry(&ctx->tx_ready_list, struct tls_rec, list);
+	rec = list_first_entry(&ctx->tx_list, struct tls_rec, list);
 	if (!rec)
 		return false;
 
-	seq = be64_to_cpup((const __be64 *)&rec->aad_space);
-	if (seq == tls_ctx->tx_seq_number)
-		return true;
-	else
-		return false;
+	return READ_ONCE(rec->tx_ready);
 }
 
 struct sk_buff *

net/tls/tls_main.c

@@ -212,7 +212,7 @@ int tls_push_pending_closed_record(struct sock *sk,
 	struct tls_sw_context_tx *ctx = tls_sw_ctx_tx(tls_ctx);
 
 	if (tls_is_partially_sent_record(tls_ctx) ||
-	    !list_empty(&ctx->tx_ready_list))
+	    !list_empty(&ctx->tx_list))
 		return tls_tx_records(sk, flags);
 	else
 		return tls_ctx->push_pending_record(sk, flags);
@@ -233,7 +233,7 @@ static void tls_write_space(struct sock *sk)
 	}
 
 	/* Schedule the transmission if tx list is ready */
-	if (is_tx_ready(ctx, tx_ctx) && !sk->sk_write_pending) {
+	if (is_tx_ready(tx_ctx) && !sk->sk_write_pending) {
 		/* Schedule the transmission */
 		if (!test_and_set_bit(BIT_TX_SCHEDULED, &tx_ctx->tx_bitmask))
 			schedule_delayed_work(&tx_ctx->tx_work.work, 0);

net/tls/tls_sw.c

@@ -329,29 +329,6 @@ static void tls_free_both_sg(struct sock *sk)
 		&rec->sg_plaintext_size);
 }
 
-static bool append_tx_ready_list(struct tls_context *tls_ctx,
-				 struct tls_sw_context_tx *ctx,
-				 struct tls_rec *enc_rec)
-{
-	u64 new_seq = be64_to_cpup((const __be64 *)&enc_rec->aad_space);
-	struct list_head *pos;
-
-	/* Need to insert encrypted record in tx_ready_list sorted
-	 * as per sequence number. Traverse linked list from tail.
-	 */
-	list_for_each_prev(pos, &ctx->tx_ready_list) {
-		struct tls_rec *rec = (struct tls_rec *)pos;
-		u64 seq = be64_to_cpup((const __be64 *)&rec->aad_space);
-
-		if (new_seq > seq)
-			break;
-	}
-
-	list_add((struct list_head *)&enc_rec->list, pos);
-
-	return is_tx_ready(tls_ctx, ctx);
-}
-
 int tls_tx_records(struct sock *sk, int flags)
 {
 	struct tls_context *tls_ctx = tls_get_ctx(sk);
@@ -360,7 +337,7 @@ int tls_tx_records(struct sock *sk, int flags)
 	int tx_flags, rc = 0;
 
 	if (tls_is_partially_sent_record(tls_ctx)) {
-		rec = list_first_entry(&ctx->tx_ready_list,
+		rec = list_first_entry(&ctx->tx_list,
 				       struct tls_rec, list);
 
 		if (flags == -1)
@@ -373,18 +350,15 @@ int tls_tx_records(struct sock *sk, int flags)
 			goto tx_err;
 
 		/* Full record has been transmitted.
-		 * Remove the head of tx_ready_list
+		 * Remove the head of tx_list
 		 */
-		tls_ctx->tx_seq_number++;
 		list_del(&rec->list);
 		kfree(rec);
 	}
 
-	/* Tx all ready records which have expected sequence number */
-	list_for_each_entry_safe(rec, tmp, &ctx->tx_ready_list, list) {
-		u64 seq = be64_to_cpup((const __be64 *)&rec->aad_space);
-
-		if (seq == tls_ctx->tx_seq_number) {
+	/* Tx all ready records */
+	list_for_each_entry_safe(rec, tmp, &ctx->tx_list, list) {
+		if (READ_ONCE(rec->tx_ready)) {
 			if (flags == -1)
 				tx_flags = rec->tx_flags;
 			else
@@ -396,7 +370,6 @@ int tls_tx_records(struct sock *sk, int flags)
 			if (rc)
 				goto tx_err;
 
-			tls_ctx->tx_seq_number++;
 			list_del(&rec->list);
 			kfree(rec);
 		} else {
@@ -446,9 +419,18 @@ static void tls_encrypt_done(struct crypto_async_request *req, int err)
 		}
 	}
 
-	/* Append the record in tx queue */
-	if (rec)
-		ready = append_tx_ready_list(tls_ctx, ctx, rec);
+	if (rec) {
+		struct tls_rec *first_rec;
+
+		/* Mark the record as ready for transmission */
+		smp_store_mb(rec->tx_ready, true);
+
+		/* If received record is at head of tx_list, schedule tx */
+		first_rec = list_first_entry(&ctx->tx_list,
+					     struct tls_rec, list);
+		if (rec == first_rec)
+			ready = true;
+	}
 
 	pending = atomic_dec_return(&ctx->encrypt_pending);
 
@@ -484,6 +466,8 @@ static int tls_do_encryption(struct sock *sk,
 	aead_request_set_callback(aead_req, CRYPTO_TFM_REQ_MAY_BACKLOG,
 				  tls_encrypt_done, sk);
 
+	/* Add the record in tx_list */
+	list_add_tail((struct list_head *)&rec->list, &ctx->tx_list);
 	atomic_inc(&ctx->encrypt_pending);
 
 	rc = crypto_aead_encrypt(aead_req);
@@ -493,9 +477,12 @@ static int tls_do_encryption(struct sock *sk,
 		rec->sg_encrypted_data[0].length += tls_ctx->tx.prepend_size;
 	}
 
-	/* Case of encryption failure */
-	if (rc && rc != -EINPROGRESS)
+	if (!rc) {
+		WRITE_ONCE(rec->tx_ready, true);
+	} else if (rc != -EINPROGRESS) {
+		list_del(&rec->list);
 		return rc;
+	}
 
 	/* Unhook the record from context if encryption is not failure */
 	ctx->open_rec = NULL;
@@ -544,13 +531,7 @@ static int tls_push_record(struct sock *sk, int flags,
 		return rc;
 	}
 
-	/* Put the record in tx_ready_list and start tx if permitted.
-	 * This happens only when encryption is not asynchronous.
-	 */
-	if (append_tx_ready_list(tls_ctx, ctx, rec))
-		return tls_tx_records(sk, flags);
-
-	return 0;
+	return tls_tx_records(sk, flags);
 }
 
 static int tls_sw_push_pending_record(struct sock *sk, int flags)
@@ -1566,7 +1547,7 @@ void tls_sw_free_resources_tx(struct sock *sk)
 	/* Tx whatever records we can transmit and abandon the rest */
 	tls_tx_records(sk, -1);
 
-	/* Free up un-sent records in tx_ready_list. First, free
+	/* Free up un-sent records in tx_list. First, free
 	 * the partially sent record if any at head of tx_list.
 	 */
 	if (tls_ctx->partially_sent_record) {
@@ -1583,13 +1564,13 @@ void tls_sw_free_resources_tx(struct sock *sk)
 
 		tls_ctx->partially_sent_record = NULL;
 
-		rec = list_first_entry(&ctx->tx_ready_list,
+		rec = list_first_entry(&ctx->tx_list,
 				       struct tls_rec, list);
 		list_del(&rec->list);
 		kfree(rec);
 	}
 
-	list_for_each_entry_safe(rec, tmp, &ctx->tx_ready_list, list) {
+	list_for_each_entry_safe(rec, tmp, &ctx->tx_list, list) {
 		free_sg(sk, rec->sg_encrypted_data,
 			&rec->sg_encrypted_num_elem,
 			&rec->sg_encrypted_size);
@@ -1633,7 +1614,7 @@ void tls_sw_free_resources_rx(struct sock *sk)
 	kfree(ctx);
 }
 
-/* The work handler to transmitt the encrypted records in tx_ready_list */
+/* The work handler to transmitt the encrypted records in tx_list */
 static void tx_work_handler(struct work_struct *work)
 {
 	struct delayed_work *delayed_work = to_delayed_work(work);
@@ -1700,7 +1681,7 @@ int tls_set_sw_offload(struct sock *sk, struct tls_context *ctx, int tx)
 		crypto_info = &ctx->crypto_send.info;
 		cctx = &ctx->tx;
 		aead = &sw_ctx_tx->aead_send;
-		INIT_LIST_HEAD(&sw_ctx_tx->tx_ready_list);
+		INIT_LIST_HEAD(&sw_ctx_tx->tx_list);
 		INIT_DELAYED_WORK(&sw_ctx_tx->tx_work.work, tx_work_handler);
 		sw_ctx_tx->tx_work.sk = sk;
 	} else {
@@ -1789,8 +1770,6 @@ int tls_set_sw_offload(struct sock *sk, struct tls_context *ctx, int tx)
 		sw_ctx_rx->sk_poll = sk->sk_socket->ops->poll;
 
 		strp_check_rcv(&sw_ctx_rx->strp);
-	} else {
-		ctx->tx_seq_number = be64_to_cpup((const __be64 *)rec_seq);
 	}
 
 	goto out;