On Thu, 2020-05-14 at 13:13 -0700, Mat Martineau wrote:
> On Wed, 13 May 2020, Paolo Abeni wrote:
>
> > MP_JOIN subflows must not land into the accept queue.
> > Currently tcp_check_req() calls an mptcp specific helper
> > to detect such scenario.
> >
> > Such helper leverages the subflow context to check for
> > MP_JOIN subflows. We need to deal also with MP JOIN
> > failures, even when the subflow context is not available
> > due allocation failure.
> >
> > A possible solution would be changing the syn_recv_sock()
> > signature to allow returning a more descriptive action/
> > error code and deal with that in tcp_check_req().
> >
> > Since the above need is MPTCP specific, this patch instead
> > uses a TCP request socket hole to add a MPTCP specific flag.
> > Such flag is used by the MPTCP syn_recv_sock() to tell
> > tcp_check_req() how to deal with the request socket.
> >
> > This change is a no-op for !MPTCP build, and makes the
> > MPTCP code simpler. It allows also the next patch to deal
> > correctly with MP JOIN failure.
> >
> > RFC -> v1:
> > - move the drop_req bit inside tcp_request_sock (Eric)
> >
> > Signed-off-by: Paolo Abeni <pab...@redhat.com>
> > ---
> > include/linux/tcp.h | 3 +++
> > include/net/mptcp.h | 17 ++++++++++-------
> > net/ipv4/tcp_minisocks.c | 2 +-
> > net/mptcp/protocol.c | 7 -------
> > net/mptcp/subflow.c | 2 ++
> > 5 files changed, 16 insertions(+), 15 deletions(-)
> >
> > diff --git a/include/linux/tcp.h b/include/linux/tcp.h
> > index e60db06ec28d..bf44e85d709d 100644
> > --- a/include/linux/tcp.h
> > +++ b/include/linux/tcp.h
> > @@ -120,6 +120,9 @@ struct tcp_request_sock {
> > u64 snt_synack; /* first SYNACK sent time */
> > bool tfo_listener;
> > bool is_mptcp;
> > +#if IS_ENABLED(CONFIG_MPTCP)
> > + bool drop_req;
> > +#endif
> > u32 txhash;
> > u32 rcv_isn;
> > u32 snt_isn;
> > diff --git a/include/net/mptcp.h b/include/net/mptcp.h
> > index e60275659de6..c4a6ef4ba35b 100644
> > --- a/include/net/mptcp.h
> > +++ b/include/net/mptcp.h
> > @@ -68,6 +68,11 @@ static inline bool rsk_is_mptcp(const struct
> > request_sock *req)
> > return tcp_rsk(req)->is_mptcp;
> > }
> >
> > +static inline bool rsk_drop_req(const struct request_sock *req)
> > +{
> > + return tcp_rsk(req)->is_mptcp && tcp_rsk(req)->drop_req;
> > +}
> > +
> > void mptcp_space(const struct sock *ssk, int *space, int *full_space);
> > bool mptcp_syn_options(struct sock *sk, const struct sk_buff *skb,
> > unsigned int *size, struct mptcp_out_options *opts);
> > @@ -121,8 +126,6 @@ static inline bool mptcp_skb_can_collapse(const struct
> > sk_buff *to,
> > skb_ext_find(from, SKB_EXT_MPTCP));
> > }
> >
> > -bool mptcp_sk_is_subflow(const struct sock *sk);
> > -
> > void mptcp_seq_show(struct seq_file *seq);
> > #else
> >
> > @@ -140,6 +143,11 @@ static inline bool rsk_is_mptcp(const struct
> > request_sock *req)
> > return false;
> > }
> >
> > +static inline bool rsk_drop_req(const struct request_sock *req)
> > +{
> > + return false;
> > +}
> > +
> > static inline void mptcp_parse_option(const struct sk_buff *skb,
> > const unsigned char *ptr, int opsize,
> > struct tcp_options_received *opt_rx)
> > @@ -190,11 +198,6 @@ static inline bool mptcp_skb_can_collapse(const struct
> > sk_buff *to,
> > return true;
> > }
> >
> > -static inline bool mptcp_sk_is_subflow(const struct sock *sk)
> > -{
> > - return false;
> > -}
> > -
> > static inline void mptcp_space(const struct sock *ssk, int *s, int *fs) { }
> > static inline void mptcp_seq_show(struct seq_file *seq) { }
> > #endif /* CONFIG_MPTCP */
> > diff --git a/net/ipv4/tcp_minisocks.c b/net/ipv4/tcp_minisocks.c
> > index 7e40322cc5ec..495dda2449fe 100644
> > --- a/net/ipv4/tcp_minisocks.c
> > +++ b/net/ipv4/tcp_minisocks.c
> > @@ -774,7 +774,7 @@ struct sock *tcp_check_req(struct sock *sk, struct
> > sk_buff *skb,
> > if (!child)
> > goto listen_overflow;
> >
> > - if (own_req && sk_is_mptcp(child) && mptcp_sk_is_subflow(child)) {
> > + if (own_req && rsk_drop_req(req)) {
> > reqsk_queue_removed(&inet_csk(sk)->icsk_accept_queue, req);
> > inet_csk_reqsk_queue_drop_and_put(sk, req);
> > return child;
> > diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c
> > index 6a812dd8b6b6..b974898eb6b5 100644
> > --- a/net/mptcp/protocol.c
> > +++ b/net/mptcp/protocol.c
> > @@ -1687,13 +1687,6 @@ bool mptcp_finish_join(struct sock *sk)
> > return ret;
> > }
> >
> > -bool mptcp_sk_is_subflow(const struct sock *sk)
> > -{
> > - struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(sk);
> > -
> > - return subflow->mp_join == 1;
> > -}
> > -
> > static bool mptcp_memory_free(const struct sock *sk, int wake)
> > {
> > struct mptcp_sock *msk = mptcp_sk(sk);
> > diff --git a/net/mptcp/subflow.c b/net/mptcp/subflow.c
> > index 009d5c478062..42a8a650ff20 100644
> > --- a/net/mptcp/subflow.c
> > +++ b/net/mptcp/subflow.c
> > @@ -500,6 +500,7 @@ static struct sock *subflow_syn_recv_sock(const struct
> > sock *sk,
> > ctx->remote_key = mp_opt.sndr_key;
> > ctx->fully_established = mp_opt.mp_capable;
> > ctx->can_ack = mp_opt.mp_capable;
> > + tcp_rsk(req)->drop_req = false;
> > } else if (ctx->mp_join) {
> > struct mptcp_sock *owner;
> >
> > @@ -512,6 +513,7 @@ static struct sock *subflow_syn_recv_sock(const struct
> > sock *sk,
> > goto close_child;
> >
> > SUBFLOW_REQ_INC_STATS(req, MPTCP_MIB_JOINACKRX);
> > + tcp_rsk(req)->drop_req = true;
> > }
>
> It looks like tcp_rsk(req)->drop_req gets initialized when the
> ctx->mp_capable and ctx->mp_join values are set as expected, but it's hard
> to tell if it's guaranteed to be initialized in every corner case (any
> allocation or token failures, unexpected input, etc.).
>
> Patch 3 will set drop_req for some cases, but does it makes sense to
> set tcp_rsk(req)->drop_req in subflow_v{4,6}_init_req() here as an
> additional 'else' clause?
We already have such check in place in subflow_ulp_clone(): if both
subflow_req->mp_join and subflow_req->mp_capable are cleared we
fallback, elsewhere we set either subflow->mp_capable or subflow-
>mp_join.
Later in subflow_ulp_clone() we have similar scenario, where do:
} else if (subflow_req->mp_join) {
while we could simply use a plain 'else'.
To make things clearer, I can replace both 'else if'... with plain else
(possibly in a separate patch), WDYT?
Thanks,
Paolo
