Paolo -
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?
}
--
2.21.3
--
Mat Martineau
Intel
