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net/tls: Consume empty data records in tls_sw_read_sock()

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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: 662fbcec32 ("net/tls: implement ->read_sock()")
Signed-off-by: Chuck Lever <cel@kernel.org>
Reviewed-by: Sabrina Dubroca <sd@queasysnail.net>
Link: https://patch.msgid.link/20260630191551.875664-1-cel@kernel.org
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
This commit is contained in:
Chuck Lever 2026-06-30 15:15:51 -04:00 committed by Paolo Abeni
parent 9e05e91a9a
commit 3be28e2c9c
1 changed files with 11 additions and 0 deletions
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11
net/tls/tls_sw.c
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@ -2115,6 +2115,17 @@ int tls_sw_read_sock(struct sock *sk, read_descriptor_t *desc,
goto read_sock_requeue;
}
/* An empty data record (legal in TLS 1.3) gives a zero
* read_actor return, indistinguishable from the consumer
* stalling; the used <= 0 path would requeue it at the
* head of rx_list and block all later records. Consume it
* here instead.
*/
if (rxm->full_len == 0) {
consume_skb(skb);
continue;
}
used = read_actor(desc, skb, rxm->offset, rxm->full_len);
if (used <= 0) {
if (!copied)