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mptcp: fix NULL ptr dereference in MP_JOIN error path

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When token lookup on MP_JOIN 3rd ack fails, the server
socket closes with a reset the incoming child. Such socket
has the 'is_mptcp' flag set, but no msk socket associated
- due to the failed lookup.

While crafting the reset packet mptcp_established_options_mp()
will try to dereference the child's master socket, causing
a NULL ptr dereference.

This change addresses the issue with explicit fallback to
TCP in such error path.

Fixes: 729cd6436f ("mptcp: cope better with MP_JOIN failure")
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Paolo Abeni 2020-05-29 17:49:18 +02:00 committed by David S. Miller
parent b0c19ed608
commit 39884604b1
1 changed files with 16 additions and 4 deletions
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20
net/mptcp/subflow.c
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@ -413,6 +413,20 @@ static void subflow_ulp_fallback(struct sock *sk,
tcp_sk(sk)->is_mptcp = 0;
}
static void subflow_drop_ctx(struct sock *ssk)
{
struct mptcp_subflow_context *ctx = mptcp_subflow_ctx(ssk);
if (!ctx)
return;
subflow_ulp_fallback(ssk, ctx);
if (ctx->conn)
sock_put(ctx->conn);
kfree_rcu(ctx, rcu);
}
static struct sock *subflow_syn_recv_sock(const struct sock *sk,
struct sk_buff *skb,
struct request_sock *req,
@ -485,10 +499,7 @@ static struct sock *subflow_syn_recv_sock(const struct sock *sk,
if (fallback_is_fatal)
goto dispose_child;
if (ctx) {
subflow_ulp_fallback(child, ctx);
kfree_rcu(ctx, rcu);
}
subflow_drop_ctx(child);
goto out;
}
@ -537,6 +548,7 @@ static struct sock *subflow_syn_recv_sock(const struct sock *sk,
return child;
dispose_child:
subflow_drop_ctx(child);
tcp_rsk(req)->drop_req = true;
tcp_send_active_reset(child, GFP_ATOMIC);
inet_csk_prepare_for_destroy_sock(child);