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sctp: subtract sctphdr len in sctp_transport_pl_hlen

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[ 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>
This commit is contained in:
Xin Long 2021-10-28 05:36:03 -04:00 committed by Greg Kroah-Hartman
parent 118eedc006
commit 554153b1cd
1 changed files with 2 additions and 1 deletions
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3
include/net/sctp/sctp.h
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@ -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)