[PATCH 5.14 532/849] sctp: subtract sctphdr len in sctp_transport_pl_hlen

Greg Kroah-Hartman
2021-11-15T23:09:41Z

From: Xin Long <lucien.xin@gmail.com>

[ Upstream commit cc4665ca646c96181a7c00198aa72c59e0c576e8 ]

sctp_transport_pl_hlen() is called to calculate the outer header length
for PL. However, as the Figure in rfc8899#section-4.4:

Any additional
headers .--- MPS -----.
| | |
v v v
+------------------------------+
| IP | ** | PL | protocol data |
+------------------------------+

<----- PLPMTU ----->
<---------- PMTU -------------->

Outer header are IP + Any additional headers, which doesn't include
Packetization Layer itself header, namely sctphdr, whereas sctphdr
is counted by __sctp_mtu_payload().

The incorrect calculation caused the link pathmtu to be set larger
than expected by t->pl.pmtu + sctp_transport_pl_hlen(). This patch
is to fix it by subtracting sctphdr len in sctp_transport_pl_hlen().

Fixes: d9e2e410ae30 ("sctp: add the constants/variables and states and some APIs for transport")
Signed-off-by: Xin Long <lucien.xin@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
include/net/sctp/sctp.h | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/include/net/sctp/sctp.h b/include/net/sctp/sctp.h
index bc00410223b03..189fdb9db1622 100644
--- a/include/net/sctp/sctp.h
+++ b/include/net/sctp/sctp.h
@@ -626,7 +626,8 @@ static inline __u32 sctp_min_frag_point(struct sctp_sock *sp, __u16 datasize)

static inline int sctp_transport_pl_hlen(struct sctp_transport *t)
{
- return __sctp_mtu_payload(sctp_sk(t->asoc->base.sk), t, 0, 0);
+ return __sctp_mtu_payload(sctp_sk(t->asoc->base.sk), t, 0, 0) -
+ sizeof(struct sctphdr);
}

static inline void sctp_transport_pl_reset(struct sctp_transport *t)
--
2.33.0