netdev - [PATCH net 2/2] net/tls: replace the sleeping lock around RX resync with a bit lock

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Date:   Fri, 31 May 2019 20:12:01 -0700
From:   Jakub Kicinski <jakub.kicinski@...ronome.com>
To:     davem@...emloft.net
Cc:     netdev@...r.kernel.org, oss-drivers@...ronome.com,
        alexei.starovoitov@...il.com,
        Jakub Kicinski <jakub.kicinski@...ronome.com>
Subject: [PATCH net 2/2] net/tls: replace the sleeping lock around RX resync with a bit lock

Commit 38030d7cb779 ("net/tls: avoid NULL-deref on resync during device removal")
tried to fix a potential NULL-dereference by taking the
context rwsem.  Unfortunately the RX resync may get called
from soft IRQ, so we can't use the rwsem to protect from
the device disappearing.  Because we are guaranteed there
can be only one resync at a time (it's called from strparser)
use a bit to indicate resync is busy and make device
removal wait for the bit to get cleared.

Note that there is a leftover "flags" field in struct
tls_context already.

Fixes: 4799ac81e52a ("tls: Add rx inline crypto offload")
Signed-off-by: Jakub Kicinski <jakub.kicinski@...ronome.com>
---
 include/net/tls.h    |  4 ++++
 net/tls/tls_device.c | 26 +++++++++++++++++++++-----
 2 files changed, 25 insertions(+), 5 deletions(-)

diff --git a/include/net/tls.h b/include/net/tls.h
index 39ea62f0c1f6..4a55ce6a303f 100644
--- a/include/net/tls.h
+++ b/include/net/tls.h
@@ -209,6 +209,10 @@ struct tls_offload_context_tx {
 	(ALIGN(sizeof(struct tls_offload_context_tx), sizeof(void *)) +        \
 	 TLS_DRIVER_STATE_SIZE)
 
+enum tls_context_flags {
+	TLS_RX_SYNC_RUNNING = 0,
+};
+
 struct cipher_context {
 	char *iv;
 	char *rec_seq;
diff --git a/net/tls/tls_device.c b/net/tls/tls_device.c
index 49b3a2ff8ef3..ed1c5db88eb0 100644
--- a/net/tls/tls_device.c
+++ b/net/tls/tls_device.c
@@ -550,6 +550,19 @@ void tls_device_write_space(struct sock *sk, struct tls_context *ctx)
 	}
 }
 
+static void tls_device_resync_rx(struct tls_context *tls_ctx,
+				 struct sock *sk, u32 seq, u64 rcd_sn)
+{
+	struct net_device *netdev;
+
+	if (WARN_ON(test_and_set_bit(TLS_RX_SYNC_RUNNING, &tls_ctx->flags)))
+		return;
+	netdev = READ_ONCE(tls_ctx->netdev);
+	if (netdev)
+		netdev->tlsdev_ops->tls_dev_resync_rx(netdev, sk, seq, rcd_sn);
+	clear_bit_unlock(TLS_RX_SYNC_RUNNING, &tls_ctx->flags);
+}
+
 void handle_device_resync(struct sock *sk, u32 seq, u64 rcd_sn)
 {
 	struct tls_context *tls_ctx = tls_get_ctx(sk);
@@ -568,10 +581,10 @@ void handle_device_resync(struct sock *sk, u32 seq, u64 rcd_sn)
 	is_req_pending = resync_req;
 
 	if (unlikely(is_req_pending) && req_seq == seq &&
-	    atomic64_try_cmpxchg(&rx_ctx->resync_req, &resync_req, 0))
-		netdev->tlsdev_ops->tls_dev_resync_rx(netdev, sk,
-						      seq + TLS_HEADER_SIZE - 1,
-						      rcd_sn);
+	    atomic64_try_cmpxchg(&rx_ctx->resync_req, &resync_req, 0)) {
+		seq += TLS_HEADER_SIZE - 1;
+		tls_device_resync_rx(tls_ctx, sk, seq, rcd_sn);
+	}
 }
 
 static int tls_device_reencrypt(struct sock *sk, struct sk_buff *skb)
@@ -972,7 +985,10 @@ static int tls_device_down(struct net_device *netdev)
 		if (ctx->rx_conf == TLS_HW)
 			netdev->tlsdev_ops->tls_dev_del(netdev, ctx,
 							TLS_OFFLOAD_CTX_DIR_RX);
-		ctx->netdev = NULL;
+		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);
 
-- 
2.21.0