Re: [PATCH net 2/2] net/tls: Fix use-after-free after the TLS device goes down and up

[Maxim Mikityanskiy <maximmi@nvidia.com>]

On 2021-05-24 19:15, Jakub Kicinski wrote:
> On Mon, 24 May 2021 15:12:20 +0300 Maxim Mikityanskiy wrote:
>> @@ -1290,6 +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);
> 
> Can we have the Rx resync take the device_offload_lock for read instead?
> Like Tx already does?

I believe you previously made this attempt in commit 38030d7cb779 
("net/tls: avoid NULL-deref on resync during device removal"), and this 
approach turned out to be problematic, as explained in commit 
e52972c11d6b ("net/tls: replace the sleeping lock around RX resync with 
a bit lock"): "RX resync may get called from soft IRQ, so we can't use 
the rwsem".

> 
>> +EXPORT_SYMBOL_GPL(tls_validate_xmit_skb_sw);
> 
> Why the export?

Because tls_validate_xmit_skb was also exported. Now I see it's needed 
for tls_validate_xmit_skb, because tls_is_sk_tx_device_offloaded needs 
its address and can be called from the drivers. There is no similar 
public function for tls_validate_xmit_skb_sw, so you are probably right 
that we don't need to export it.

>