net/tls: Remove the context from the list in tls_device_down

tls_device_down takes a reference on all contexts it's going to move to
the degraded state (software fallback). If sk_destruct runs afterwards,
it can reduce the reference counter back to 1 and return early without
destroying the context. Then tls_device_down will release the reference
it took and call tls_device_free_ctx. However, the context will still
stay in tls_device_down_list forever. The list will contain an item,
memory for which is released, making a memory corruption possible.

Fix the above bug by properly removing the context from all lists before
any call to tls_device_free_ctx.

Fixes: 3740651b ("tls: Fix context leak on tls_device_down")
Signed-off-by: Maxim Mikityanskiy <maximmi@nvidia.com>
Reviewed-by: Tariq Toukan <tariqt@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/tls/tls_device.c

@@ -1376,9 +1376,14 @@ static int tls_device_down(struct net_device *netdev)
 		 * by tls_device_free_ctx. rx_conf and tx_conf stay in TLS_HW.
 		 * Now release the ref taken above.
 		 */
-		if (refcount_dec_and_test(&ctx->refcount))
+		if (refcount_dec_and_test(&ctx->refcount)) {
+			/* sk_destruct ran after tls_device_down took a ref, and
+			 * it returned early. Complete the destruction here.
+			 */
+			list_del(&ctx->list);
 			tls_device_free_ctx(ctx);
 		}
+	}
 
 	up_write(&device_offload_lock);