Merge branch 'ktls-use-after-free'

Maxim Mikityanskiy says:

====================
Fix use-after-free after the TLS device goes down and up

This small series fixes a use-after-free bug in the TLS offload code.
The first patch is a preparation for the second one, and the second is
the fix itself.

v2 changes:

Remove unneeded EXPORT_SYMBOL_GPL.
====================

Acked-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/tls.h

@@ -193,7 +193,11 @@ struct tls_offload_context_tx {
 	(sizeof(struct tls_offload_context_tx) + TLS_DRIVER_STATE_SIZE_TX)
 
 enum tls_context_flags {
-	TLS_RX_SYNC_RUNNING = 0,
+	/* tls_device_down was called after the netdev went down, device state
+	 * was released, and kTLS works in software, even though rx_conf is
+	 * still TLS_HW (needed for transition).
+	 */
+	TLS_RX_DEV_DEGRADED = 0,
 	/* Unlike RX where resync is driven entirely by the core in TX only
 	 * the driver knows when things went out of sync, so we need the flag
 	 * to be atomic.
@@ -266,6 +270,7 @@ struct tls_context {
 
 	/* cache cold stuff */
 	struct proto *sk_proto;
+	struct sock *sk;
 
 	void (*sk_destruct)(struct sock *sk);
 
@@ -448,6 +453,9 @@ static inline u16 tls_user_config(struct tls_context *ctx, bool tx)
 struct sk_buff *
 tls_validate_xmit_skb(struct sock *sk, struct net_device *dev,
 		      struct sk_buff *skb);
+struct sk_buff *
+tls_validate_xmit_skb_sw(struct sock *sk, struct net_device *dev,
+			 struct sk_buff *skb);
 
 static inline bool tls_is_sk_tx_device_offloaded(struct sock *sk)
 {

net/tls/tls_device.c

@@ -50,6 +50,7 @@ static void tls_device_gc_task(struct work_struct *work);
 static DECLARE_WORK(tls_device_gc_work, tls_device_gc_task);
 static LIST_HEAD(tls_device_gc_list);
 static LIST_HEAD(tls_device_list);
+static LIST_HEAD(tls_device_down_list);
 static DEFINE_SPINLOCK(tls_device_lock);
 
 static void tls_device_free_ctx(struct tls_context *ctx)
@@ -680,15 +681,13 @@ static void tls_device_resync_rx(struct tls_context *tls_ctx,
 	struct tls_offload_context_rx *rx_ctx = tls_offload_ctx_rx(tls_ctx);
 	struct net_device *netdev;
 
-	if (WARN_ON(test_and_set_bit(TLS_RX_SYNC_RUNNING, &tls_ctx->flags)))
-		return;
-
 	trace_tls_device_rx_resync_send(sk, seq, rcd_sn, rx_ctx->resync_type);
+	rcu_read_lock();
 	netdev = READ_ONCE(tls_ctx->netdev);
 	if (netdev)
 		netdev->tlsdev_ops->tls_dev_resync(netdev, sk, seq, rcd_sn,
 						   TLS_OFFLOAD_CTX_DIR_RX);
-	clear_bit_unlock(TLS_RX_SYNC_RUNNING, &tls_ctx->flags);
+	rcu_read_unlock();
 	TLS_INC_STATS(sock_net(sk), LINUX_MIB_TLSRXDEVICERESYNC);
 }
 
@@ -761,6 +760,8 @@ void tls_device_rx_resync_new_rec(struct sock *sk, u32 rcd_len, u32 seq)
 
 	if (tls_ctx->rx_conf != TLS_HW)
 		return;
+	if (unlikely(test_bit(TLS_RX_DEV_DEGRADED, &tls_ctx->flags)))
+		return;
 
 	prot = &tls_ctx->prot_info;
 	rx_ctx = tls_offload_ctx_rx(tls_ctx);
@@ -963,6 +964,17 @@ int tls_device_decrypted(struct sock *sk, struct tls_context *tls_ctx,
 
 	ctx->sw.decrypted |= is_decrypted;
 
+	if (unlikely(test_bit(TLS_RX_DEV_DEGRADED, &tls_ctx->flags))) {
+		if (likely(is_encrypted || is_decrypted))
+			return 0;
+
+		/* After tls_device_down disables the offload, the next SKB will
+		 * likely have initial fragments decrypted, and final ones not
+		 * decrypted. We need to reencrypt that single SKB.
+		 */
+		return tls_device_reencrypt(sk, skb);
+	}
+
 	/* Return immediately if the record is either entirely plaintext or
 	 * entirely ciphertext. Otherwise handle reencrypt partially decrypted
 	 * record.
@@ -1292,6 +1304,26 @@ static int tls_device_down(struct net_device *netdev)
 	spin_unlock_irqrestore(&tls_device_lock, flags);
 
 	list_for_each_entry_safe(ctx, tmp, &list, list)	{
+		/* Stop offloaded TX and switch to the fallback.
+		 * tls_is_sk_tx_device_offloaded will return false.
+		 */
+		WRITE_ONCE(ctx->sk->sk_validate_xmit_skb, tls_validate_xmit_skb_sw);
+
+		/* Stop the RX and TX resync.
+		 * tls_dev_resync must not be called after tls_dev_del.
+		 */
+		WRITE_ONCE(ctx->netdev, NULL);
+
+		/* Start skipping the RX resync logic completely. */
+		set_bit(TLS_RX_DEV_DEGRADED, &ctx->flags);
+
+		/* Sync with inflight packets. After this point:
+		 * TX: no non-encrypted packets will be passed to the driver.
+		 * RX: resync requests from the driver will be ignored.
+		 */
+		synchronize_net();
+
+		/* Release the offload context on the driver side. */
 		if (ctx->tx_conf == TLS_HW)
 			netdev->tlsdev_ops->tls_dev_del(netdev, ctx,
 							TLS_OFFLOAD_CTX_DIR_TX);
@@ -1299,15 +1331,21 @@ static int tls_device_down(struct net_device *netdev)
 		    !test_bit(TLS_RX_DEV_CLOSED, &ctx->flags))
 			netdev->tlsdev_ops->tls_dev_del(netdev, ctx,
 							TLS_OFFLOAD_CTX_DIR_RX);
-		WRITE_ONCE(ctx->netdev, NULL);
-		smp_mb__before_atomic(); /* pairs with test_and_set_bit() */
-		while (test_bit(TLS_RX_SYNC_RUNNING, &ctx->flags))
-			usleep_range(10, 200);
-		dev_put(netdev);
-		list_del_init(&ctx->list);
 
-		if (refcount_dec_and_test(&ctx->refcount))
-			tls_device_free_ctx(ctx);
+		dev_put(netdev);
+
+		/* Move the context to a separate list for two reasons:
+		 * 1. When the context is deallocated, list_del is called.
+		 * 2. It's no longer an offloaded context, so we don't want to
+		 *    run offload-specific code on this context.
+		 */
+		spin_lock_irqsave(&tls_device_lock, flags);
+		list_move_tail(&ctx->list, &tls_device_down_list);
+		spin_unlock_irqrestore(&tls_device_lock, flags);
+
+		/* Device contexts for RX and TX will be freed in on sk_destruct
+		 * by tls_device_free_ctx. rx_conf and tx_conf stay in TLS_HW.
+		 */
 	}
 
 	up_write(&device_offload_lock);

net/tls/tls_device_fallback.c

@@ -431,6 +431,13 @@ struct sk_buff *tls_validate_xmit_skb(struct sock *sk,
 }
 EXPORT_SYMBOL_GPL(tls_validate_xmit_skb);
 
+struct sk_buff *tls_validate_xmit_skb_sw(struct sock *sk,
+					 struct net_device *dev,
+					 struct sk_buff *skb)
+{
+	return tls_sw_fallback(sk, skb);
+}
+
 struct sk_buff *tls_encrypt_skb(struct sk_buff *skb)
 {
 	return tls_sw_fallback(skb->sk, skb);

net/tls/tls_main.c

@@ -636,6 +636,7 @@ struct tls_context *tls_ctx_create(struct sock *sk)
 	mutex_init(&ctx->tx_lock);
 	rcu_assign_pointer(icsk->icsk_ulp_data, ctx);
 	ctx->sk_proto = READ_ONCE(sk->sk_prot);
+	ctx->sk = sk;
 	return ctx;
 }