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Merge branch 'mptcp-fix-races-on-accept'
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Paolo Abeni says:

====================
mptcp: fix races on accept()

This series includes some fixes for accept() races which may cause inconsistent
MPTCP socket status and oops. Please see the individual patches for the
technical details.
====================

Signed-off-by: David S. Miller <davem@davemloft.net>
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David S. Miller committed Apr 20, 2020
2 parents bd01942 + fca5c82 commit 0b943d9
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Showing 3 changed files with 52 additions and 33 deletions.
11 changes: 8 additions & 3 deletions net/mptcp/protocol.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -1332,7 +1332,9 @@ static struct ipv6_pinfo *mptcp_inet6_sk(const struct sock *sk)
}
#endif

struct sock *mptcp_sk_clone(const struct sock *sk, struct request_sock *req)
struct sock *mptcp_sk_clone(const struct sock *sk,
const struct tcp_options_received *opt_rx,
struct request_sock *req)
{
struct mptcp_subflow_request_sock *subflow_req = mptcp_subflow_rsk(req);
struct sock *nsk = sk_clone_lock(sk, GFP_ATOMIC);
Expand Down Expand Up @@ -1370,14 +1372,15 @@ struct sock *mptcp_sk_clone(const struct sock *sk, struct request_sock *req)

msk->write_seq = subflow_req->idsn + 1;
atomic64_set(&msk->snd_una, msk->write_seq);
if (subflow_req->remote_key_valid) {
if (opt_rx->mptcp.mp_capable) {
msk->can_ack = true;
msk->remote_key = subflow_req->remote_key;
msk->remote_key = opt_rx->mptcp.sndr_key;
mptcp_crypto_key_sha(msk->remote_key, NULL, &ack_seq);
ack_seq++;
msk->ack_seq = ack_seq;
}

sock_reset_flag(nsk, SOCK_RCU_FREE);
/* will be fully established after successful MPC subflow creation */
inet_sk_state_store(nsk, TCP_SYN_RECV);
bh_unlock_sock(nsk);
Expand Down Expand Up @@ -1779,6 +1782,8 @@ static int mptcp_listen(struct socket *sock, int backlog)
goto unlock;
}

sock_set_flag(sock->sk, SOCK_RCU_FREE);

err = ssock->ops->listen(ssock, backlog);
inet_sk_state_store(sock->sk, inet_sk_state_load(ssock->sk));
if (!err)
Expand Down
8 changes: 4 additions & 4 deletions net/mptcp/protocol.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -206,12 +206,10 @@ struct mptcp_subflow_request_sock {
struct tcp_request_sock sk;
u16 mp_capable : 1,
mp_join : 1,
backup : 1,
remote_key_valid : 1;
backup : 1;
u8 local_id;
u8 remote_id;
u64 local_key;
u64 remote_key;
u64 idsn;
u32 token;
u32 ssn_offset;
Expand Down Expand Up @@ -332,7 +330,9 @@ void mptcp_proto_init(void);
int mptcp_proto_v6_init(void);
#endif

struct sock *mptcp_sk_clone(const struct sock *sk, struct request_sock *req);
struct sock *mptcp_sk_clone(const struct sock *sk,
const struct tcp_options_received *opt_rx,
struct request_sock *req);
void mptcp_get_options(const struct sk_buff *skb,
struct tcp_options_received *opt_rx);

Expand Down
66 changes: 40 additions & 26 deletions net/mptcp/subflow.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -133,7 +133,6 @@ static void subflow_init_req(struct request_sock *req,

subflow_req->mp_capable = 0;
subflow_req->mp_join = 0;
subflow_req->remote_key_valid = 0;

#ifdef CONFIG_TCP_MD5SIG
/* no MPTCP if MD5SIG is enabled on this socket or we may run out of
Expand Down Expand Up @@ -376,6 +375,17 @@ static void mptcp_force_close(struct sock *sk)
sk_common_release(sk);
}

static void subflow_ulp_fallback(struct sock *sk,
struct mptcp_subflow_context *old_ctx)
{
struct inet_connection_sock *icsk = inet_csk(sk);

mptcp_subflow_tcp_fallback(sk, old_ctx);
icsk->icsk_ulp_ops = NULL;
rcu_assign_pointer(icsk->icsk_ulp_data, NULL);
tcp_sk(sk)->is_mptcp = 0;
}

static struct sock *subflow_syn_recv_sock(const struct sock *sk,
struct sk_buff *skb,
struct request_sock *req,
Expand All @@ -388,10 +398,12 @@ static struct sock *subflow_syn_recv_sock(const struct sock *sk,
struct tcp_options_received opt_rx;
bool fallback_is_fatal = false;
struct sock *new_msk = NULL;
bool fallback = false;
struct sock *child;

pr_debug("listener=%p, req=%p, conn=%p", listener, req, listener->conn);

opt_rx.mptcp.mp_capable = 0;
if (tcp_rsk(req)->is_mptcp == 0)
goto create_child;

Expand All @@ -406,20 +418,16 @@ static struct sock *subflow_syn_recv_sock(const struct sock *sk,
goto create_msk;
}

opt_rx.mptcp.mp_capable = 0;
mptcp_get_options(skb, &opt_rx);
if (opt_rx.mptcp.mp_capable) {
subflow_req->remote_key = opt_rx.mptcp.sndr_key;
subflow_req->remote_key_valid = 1;
} else {
subflow_req->mp_capable = 0;
if (!opt_rx.mptcp.mp_capable) {
fallback = true;
goto create_child;
}

create_msk:
new_msk = mptcp_sk_clone(listener->conn, req);
new_msk = mptcp_sk_clone(listener->conn, &opt_rx, req);
if (!new_msk)
subflow_req->mp_capable = 0;
fallback = true;
} else if (subflow_req->mp_join) {
fallback_is_fatal = true;
opt_rx.mptcp.mp_join = 0;
Expand All @@ -438,12 +446,18 @@ static struct sock *subflow_syn_recv_sock(const struct sock *sk,
if (child && *own_req) {
struct mptcp_subflow_context *ctx = mptcp_subflow_ctx(child);

/* we have null ctx on TCP fallback, which is fatal on
* MPJ handshake
/* we need to fallback on ctx allocation failure and on pre-reqs
* checking above. In the latter scenario we additionally need
* to reset the context to non MPTCP status.
*/
if (!ctx) {
if (!ctx || fallback) {
if (fallback_is_fatal)
goto close_child;

if (ctx) {
subflow_ulp_fallback(child, ctx);
kfree_rcu(ctx, rcu);
}
goto out;
}

Expand All @@ -455,6 +469,13 @@ static struct sock *subflow_syn_recv_sock(const struct sock *sk,
mptcp_pm_new_connection(mptcp_sk(new_msk), 1);
ctx->conn = new_msk;
new_msk = NULL;

/* with OoO packets we can reach here without ingress
* mpc option
*/
ctx->remote_key = opt_rx.mptcp.sndr_key;
ctx->fully_established = opt_rx.mptcp.mp_capable;
ctx->can_ack = opt_rx.mptcp.mp_capable;
} else if (ctx->mp_join) {
struct mptcp_sock *owner;

Expand All @@ -474,6 +495,13 @@ static struct sock *subflow_syn_recv_sock(const struct sock *sk,
/* dispose of the left over mptcp master, if any */
if (unlikely(new_msk))
mptcp_force_close(new_msk);

/* check for expected invariant - should never trigger, just help
* catching eariler subtle bugs
*/
WARN_ON_ONCE(*own_req && child && tcp_sk(child)->is_mptcp &&
(!mptcp_subflow_ctx(child) ||
!mptcp_subflow_ctx(child)->conn));
return child;

close_child:
Expand Down Expand Up @@ -1076,17 +1104,6 @@ static void subflow_ulp_release(struct sock *sk)
kfree_rcu(ctx, rcu);
}

static void subflow_ulp_fallback(struct sock *sk,
struct mptcp_subflow_context *old_ctx)
{
struct inet_connection_sock *icsk = inet_csk(sk);

mptcp_subflow_tcp_fallback(sk, old_ctx);
icsk->icsk_ulp_ops = NULL;
rcu_assign_pointer(icsk->icsk_ulp_data, NULL);
tcp_sk(sk)->is_mptcp = 0;
}

static void subflow_ulp_clone(const struct request_sock *req,
struct sock *newsk,
const gfp_t priority)
Expand Down Expand Up @@ -1120,9 +1137,6 @@ static void subflow_ulp_clone(const struct request_sock *req,
* is fully established only after we receive the remote key
*/
new_ctx->mp_capable = 1;
new_ctx->fully_established = subflow_req->remote_key_valid;
new_ctx->can_ack = subflow_req->remote_key_valid;
new_ctx->remote_key = subflow_req->remote_key;
new_ctx->local_key = subflow_req->local_key;
new_ctx->token = subflow_req->token;
new_ctx->ssn_offset = subflow_req->ssn_offset;
Expand Down

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