Re: [PATCH net] net/tls: Consume empty data records in tls_sw_read_sock()

[Sabrina Dubroca <sd@queasysnail.net>]

2026-06-30, 15:15:51 -0400, Chuck Lever wrote:
> A peer may send a zero-length TLS application_data record; TLS 1.3
> explicitly permits these as a traffic-analysis countermeasure (RFC
> 8446, Section 5.1). After decryption such a record has full_len ==
> 0. tls_sw_read_sock() hands it to the read_actor, which has no
> payload to consume and returns zero. The loop treats a zero return
> as backpressure (used <= 0), requeues the skb at the head of
> rx_list, and stops. rx_list is serviced head-first on the next
> call, so the empty record is dequeued, fails the same way, and is
> requeued again; every later record on the connection is blocked
> behind it.
> 
> tls_sw_recvmsg() does not stall on this: a zero-length data record
> copies nothing and falls through to consume_skb(). Mirror that in
> the read_sock() path by recognizing an empty data record before
> the actor runs, consuming it, and continuing.
> 
> Fixes: 662fbcec32f4 ("net/tls: implement ->read_sock()")
> Signed-off-by: Chuck Lever <cel@kernel.org>
> ---
>  net/tls/tls_sw.c | 11 +++++++++++
>  1 file changed, 11 insertions(+)

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

I think tls_sw_splice_read() suffers from a similar issue (returning 0
even though more data may be available). Sashiko agrees, and also
found a few more pre-existing issues.

-- 
Sabrina