@@ -376,6 +376,17 @@ 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,
@@ -388,6 +399,7 @@ 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);
@@ -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_valid = 1;
} else {
- subflow_req->mp_capable = 0;
+ fallback = true;
goto create_child;
}
create_msk:
new_msk = mptcp_sk_clone(listener->conn, 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;
@@ -438,12 +450,18 @@ 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;
}
@@ -474,6 +492,13 @@ 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:
@@ -1094,17 +1119,6 @@ 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)
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: 58b09919626b ("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> --- net/mptcp/subflow.c | 46 +++++++++++++++++++++++++++++---------------- 1 file changed, 30 insertions(+), 16 deletions(-)