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| author | Qingfang Deng <dqfext@gmail.com> | 2026-03-17 08:41:40 +0300 |
|---|---|---|
| committer | Paolo Abeni <pabeni@redhat.com> | 2026-03-19 13:00:04 +0300 |
| commit | 9f4960b94f1a044f76da98a765d6cbd294c22c92 (patch) | |
| tree | 191568d43276520bd0b4aef92c4da0c9ec7aa125 | |
| parent | 96a584db75bb21781562dc79f11932ce38a1205f (diff) | |
| download | linux-9f4960b94f1a044f76da98a765d6cbd294c22c92.tar.xz | |
l2tp: ppp: use max L2TP header size for PPP channel hdrlen
chan.hdrlen is read once at channel registration by
ppp_register_net_channel(), and used to set the PPP net device's
hard_header_len. It was set to PPPOL2TP_L2TP_HDR_SIZE_NOSEQ (6), which
is 4 bytes too small if sequence numbers are later enabled via
setsockopt(PPPOL2TP_SO_SENDSEQ), causing unnecessary skb reallocations
on the TX path.
The setsockopt handler attempted to change netdev's hard_header_len by
updating chan.hdrlen, but the PPP layer never re-reads it after the
registration, so the update had no effect.
To avoid the unnecessary reallocations, set chan.hdrlen to
PPPOL2TP_L2TP_HDR_SIZE_SEQ (10) unconditionally at registration and
remove the ineffective update in the setsockopt callback.
Signed-off-by: Qingfang Deng <dqfext@gmail.com>
Link: https://patch.msgid.link/20260317054141.524879-1-dqfext@gmail.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
| -rw-r--r-- | net/l2tp/l2tp_ppp.c | 15 |
1 files changed, 5 insertions, 10 deletions
diff --git a/net/l2tp/l2tp_ppp.c b/net/l2tp/l2tp_ppp.c index ae4543d5597b..99d6582f41de 100644 --- a/net/l2tp/l2tp_ppp.c +++ b/net/l2tp/l2tp_ppp.c @@ -787,11 +787,12 @@ static int pppol2tp_connect(struct socket *sock, struct sockaddr_unsized *userva goto out_no_ppp; } - /* The only header we need to worry about is the L2TP - * header. This size is different depending on whether - * sequence numbers are enabled for the data channel. + /* Reserve enough headroom for the L2TP header with sequence numbers, + * which is the largest possible. This is used by the PPP layer to set + * the net device's hard_header_len at registration, which must be + * sufficient regardless of whether sequence numbers are enabled later. */ - po->chan.hdrlen = PPPOL2TP_L2TP_HDR_SIZE_NOSEQ; + po->chan.hdrlen = PPPOL2TP_L2TP_HDR_SIZE_SEQ; po->chan.private = sk; po->chan.ops = &pppol2tp_chan_ops; @@ -1176,12 +1177,6 @@ static int pppol2tp_session_setsockopt(struct sock *sk, break; } session->send_seq = !!val; - { - struct pppox_sock *po = pppox_sk(sk); - - po->chan.hdrlen = val ? PPPOL2TP_L2TP_HDR_SIZE_SEQ : - PPPOL2TP_L2TP_HDR_SIZE_NOSEQ; - } l2tp_session_set_header_len(session, session->tunnel->version, session->tunnel->encap); break; |