Re: [PATCH net v2] tls: Fix race condition in tls_sw_cancel_work_tx()

[Sabrina Dubroca <sd@queasysnail.net>]

2026-02-20, 18:40:36 +0900, Hyunwoo Kim wrote:
> This issue was discovered during a code audit.
> 
> After cancel_delayed_work_sync() is called from tls_sk_proto_close(), 
> tx_work_handler() can still be scheduled from paths such as the 
> Delayed ACK handler or ksoftirqd.
> As a result, the tx_work_handler() worker may dereference a freed 
> TLS object.
> 
> The following is a simple race scenario:
> 
>           cpu0                         cpu1
> 
> tls_sk_proto_close()
>   tls_sw_cancel_work_tx()
>                                  tls_write_space()
>                                    tls_sw_write_space()
>                                      if (!test_and_set_bit(BIT_TX_SCHEDULED, &tx_ctx->tx_bitmask))
>     set_bit(BIT_TX_SCHEDULED, &ctx->tx_bitmask);
>     cancel_delayed_work_sync(&ctx->tx_work.work);
>                                      schedule_delayed_work(&tx_ctx->tx_work.work, 0);

And possibly something similar with tls_encrypt_done() if async crypto
gets delayed by just the right amount.

> To prevent this race condition, cancel_delayed_work_sync() is 
> replaced with disable_delayed_work_sync().
> 
> Fixes: f87e62d45e51 ("net/tls: remove close callback sock unlock/lock around TX work flush")
> Signed-off-by: Hyunwoo Kim <imv4bel@gmail.com>
> ---
> Changes in v2:
> - Shorten the patch subject
> - Target the net tree
> - Add the bug discovery background and the race scenario to the commit message
> - v1: https://lore.kernel.org/all/aZLotq3aZY0b-dI8@v4bel/
> ---
>  net/tls/tls_sw.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/net/tls/tls_sw.c b/net/tls/tls_sw.c
> index 9937d4c810f2..b1fa62de9dab 100644
> --- a/net/tls/tls_sw.c
> +++ b/net/tls/tls_sw.c
> @@ -2533,7 +2533,7 @@ void tls_sw_cancel_work_tx(struct tls_context *tls_ctx)
>  
>  	set_bit(BIT_TX_CLOSING, &ctx->tx_bitmask);
>  	set_bit(BIT_TX_SCHEDULED, &ctx->tx_bitmask);
> -	cancel_delayed_work_sync(&ctx->tx_work.work);
> +	disable_delayed_work_sync(&ctx->tx_work.work);

This seems ok.
Reviewed-by: Sabrina Dubroca <sd@queasysnail.net>

It would maybe be a bit "cleaner" to reorder the operations in
tls_sk_proto_close() to first stop all async encryptions and switch
the CBs so that tls_write_space can't be called anymore, and then
cancel the tx_work (once we know nothing can reschedule it anymore),
but this should be fine.

>  }
>  
>  void tls_sw_release_resources_tx(struct sock *sk)
> -- 
> 2.43.0
> 

-- 
Sabrina