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>

1 files changed, 5 insertions, 11 deletions

diff --git a/include/net/tls.h b/include/net/tls.h
index 3aa73e2d8823..1615fb5ea114 100644
--- a/include/net/tls.h
+++ b/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 *