[PATCH 5.15.y] mptcp: distinguish rcv vs sent backup flag in requests

["Matthieu Baerts (NGI0)" <matttbe@kernel.org>]

commit efd340bf3d7779a3a8ec954d8ec0fb8a10f24982 upstream.

When sending an MP_JOIN + SYN + ACK, it is possible to mark the subflow
as 'backup' by setting the flag with the same name. Before this patch,
the backup was set if the other peer set it in its MP_JOIN + SYN
request.

It is not correct: the backup flag should be set in the MPJ+SYN+ACK only
if the host asks for it, and not mirroring what was done by the other
peer. It is then required to have a dedicated bit for each direction,
similar to what is done in the subflow context.

Fixes: f296234c98a8 ("mptcp: Add handling of incoming MP_JOIN requests")
Cc: stable@vger.kernel.org
Reviewed-by: Mat Martineau <martineau@kernel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
[ Conflicts in subflow.c, because the context has changed in commit
  4cf86ae84c71 ("mptcp: strict local address ID selection"), and in
  commit 967d3c27127e ("mptcp: fix data races on remote_id"), which are
  not in this version. These commits are unrelated to this
  modification. ]
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
---
 net/mptcp/options.c  | 2 +-
 net/mptcp/protocol.h | 1 +
 net/mptcp/subflow.c  | 1 +
 3 files changed, 3 insertions(+), 1 deletion(-)

diff --git a/net/mptcp/options.c b/net/mptcp/options.c
index 3b4ce8a06f99..4d8f2f6a8f73 100644
--- a/net/mptcp/options.c
+++ b/net/mptcp/options.c
@@ -877,7 +877,7 @@ bool mptcp_synack_options(const struct request_sock *req, unsigned int *size,
 		return true;
 	} else if (subflow_req->mp_join) {
 		opts->suboptions = OPTION_MPTCP_MPJ_SYNACK;
-		opts->backup = subflow_req->backup;
+		opts->backup = subflow_req->request_bkup;
 		opts->join_id = subflow_req->local_id;
 		opts->thmac = subflow_req->thmac;
 		opts->nonce = subflow_req->local_nonce;
diff --git a/net/mptcp/protocol.h b/net/mptcp/protocol.h
index b4ccae4f6849..d2e68f5c6288 100644
--- a/net/mptcp/protocol.h
+++ b/net/mptcp/protocol.h
@@ -370,6 +370,7 @@ struct mptcp_subflow_request_sock {
 	u16	mp_capable : 1,
 		mp_join : 1,
 		backup : 1,
+		request_bkup : 1,
 		csum_reqd : 1,
 		allow_join_id0 : 1;
 	u8	local_id;
diff --git a/net/mptcp/subflow.c b/net/mptcp/subflow.c
index f96363d83e67..2fdc7b1d2f32 100644
--- a/net/mptcp/subflow.c
+++ b/net/mptcp/subflow.c
@@ -1766,6 +1766,7 @@ static void subflow_ulp_clone(const struct request_sock *req,
 		new_ctx->mp_join = 1;
 		new_ctx->fully_established = 1;
 		new_ctx->backup = subflow_req->backup;
+		new_ctx->request_bkup = subflow_req->request_bkup;
 		new_ctx->local_id = subflow_req->local_id;
 		new_ctx->remote_id = subflow_req->remote_id;
 		new_ctx->token = subflow_req->token;
-- 
2.45.2