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mptcp: avoid flipping mp_capable field in syn_recv_sock()

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If multiple CPUs races on the same req_sock in syn_recv_sock(),
flipping such field can cause inconsistent child socket status.

When racing, the CPU losing the req ownership may still change
the mptcp request socket mp_capable flag while the CPU owning
the request is cloning the socket, leaving the child socket with
'is_mptcp' set but no 'mp_capable' flag.

Such socket will stay with 'conn' field cleared, heading to oops
in later mptcp callback.

Address the issue tracking the fallback status in a local variable.

Fixes: 58b0991962 ("mptcp: create msk early")
Co-developed-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Paolo Abeni 2020-04-20 16:25:05 +02:00 • committed by David S. Miller
parent 5e20087d1b
commit 4c8941de78
1 changed files with 30 additions and 16 deletions
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46
net/mptcp/subflow.c
View file

@ -376,6 +376,17 @@ static void mptcp_force_close(struct sock *sk)
sk_common_release(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, static struct sock *subflow_syn_recv_sock(const struct sock *sk,
struct sk_buff *skb, struct sk_buff *skb,
struct request_sock *req, struct request_sock *req,
@ -388,6 +399,7 @@ static struct sock *subflow_syn_recv_sock(const struct sock *sk,
struct tcp_options_received opt_rx; struct tcp_options_received opt_rx;
bool fallback_is_fatal = false; bool fallback_is_fatal = false;
struct sock *new_msk = NULL; struct sock *new_msk = NULL;
bool fallback = false;
struct sock *child; struct sock *child;
pr_debug("listener=%p, req=%p, conn=%p", listener, req, listener->conn); pr_debug("listener=%p, req=%p, conn=%p", listener, req, listener->conn);
@ -412,14 +424,14 @@ static struct sock *subflow_syn_recv_sock(const struct sock *sk,
subflow_req->remote_key = opt_rx.mptcp.sndr_key; subflow_req->remote_key = opt_rx.mptcp.sndr_key;
subflow_req->remote_key_valid = 1; subflow_req->remote_key_valid = 1;
} else { } else {
subflow_req->mp_capable = 0; fallback = true;
goto create_child; goto create_child;
} }
create_msk: create_msk:
new_msk = mptcp_sk_clone(listener->conn, req); new_msk = mptcp_sk_clone(listener->conn, req);
if (!new_msk) if (!new_msk)
subflow_req->mp_capable = 0; fallback = true;
} else if (subflow_req->mp_join) { } else if (subflow_req->mp_join) {
fallback_is_fatal = true; fallback_is_fatal = true;
opt_rx.mptcp.mp_join = 0; opt_rx.mptcp.mp_join = 0;
@ -438,12 +450,18 @@ create_child:
if (child && *own_req) { if (child && *own_req) {
struct mptcp_subflow_context *ctx = mptcp_subflow_ctx(child); struct mptcp_subflow_context *ctx = mptcp_subflow_ctx(child);
/* we have null ctx on TCP fallback, which is fatal on /* we need to fallback on ctx allocation failure and on pre-reqs
* MPJ handshake * 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) if (fallback_is_fatal)
goto close_child; goto close_child;
if (ctx) {
subflow_ulp_fallback(child, ctx);
kfree_rcu(ctx, rcu);
}
goto out; goto out;
} }
@ -474,6 +492,13 @@ out:
/* dispose of the left over mptcp master, if any */ /* dispose of the left over mptcp master, if any */
if (unlikely(new_msk)) if (unlikely(new_msk))
mptcp_force_close(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; return child;
close_child: close_child:
@ -1076,17 +1101,6 @@ static void subflow_ulp_release(struct sock *sk)
kfree_rcu(ctx, rcu); 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, static void subflow_ulp_clone(const struct request_sock *req,
struct sock *newsk, struct sock *newsk,
const gfp_t priority) const gfp_t priority)