[PATCH mptcp-net] mptcp: fix locking in mptcp_nl_cmd_sf_destroy()

[Paolo Abeni <pabeni@redhat.com>]

The user-space PM subflow removal path uses a couple of helpers
that must be called under the msk socket lock and the current
code lacks such requirement.

Change the existing lock scope so that the relevant code is under
its protection.

Fixes: d9a4594edabf ("mptcp: netlink: Add MPTCP_PM_CMD_REMOVE")
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
---
It should close issues/287, let's see what the CI says
---
 net/mptcp/pm_userspace.c | 19 ++++++-------------
 1 file changed, 6 insertions(+), 13 deletions(-)

diff --git a/net/mptcp/pm_userspace.c b/net/mptcp/pm_userspace.c
index 3d1d365e9c6f..33be79f0e9c2 100644
--- a/net/mptcp/pm_userspace.c
+++ b/net/mptcp/pm_userspace.c
@@ -307,15 +307,11 @@ static struct sock *mptcp_nl_find_ssk(struct mptcp_sock *msk,
 				      const struct mptcp_addr_info *local,
 				      const struct mptcp_addr_info *remote)
 {
-	struct sock *sk = &msk->sk.icsk_inet.sk;
 	struct mptcp_subflow_context *subflow;
-	struct sock *found = NULL;
 
 	if (local->family != remote->family)
 		return NULL;
 
-	lock_sock(sk);
-
 	mptcp_for_each_subflow(msk, subflow) {
 		const struct inet_sock *issk;
 		struct sock *ssk;
@@ -348,16 +344,11 @@ static struct sock *mptcp_nl_find_ssk(struct mptcp_sock *msk,
 		}
 
 		if (issk->inet_sport == local->port &&
-		    issk->inet_dport == remote->port) {
-			found = ssk;
-			goto found;
-		}
+		    issk->inet_dport == remote->port)
+			return ssk;
 	}
 
-found:
-	release_sock(sk);
-
-	return found;
+	return NULL;
 }
 
 int mptcp_nl_cmd_sf_destroy(struct sk_buff *skb, struct genl_info *info)
@@ -413,6 +404,7 @@ int mptcp_nl_cmd_sf_destroy(struct sk_buff *skb, struct genl_info *info)
 	}
 
 	sk = &msk->sk.icsk_inet.sk;
+	lock_sock(sk);
 	ssk = mptcp_nl_find_ssk(msk, &addr_l, &addr_r);
 	if (ssk) {
 		struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(ssk);
@@ -424,8 +416,9 @@ int mptcp_nl_cmd_sf_destroy(struct sk_buff *skb, struct genl_info *info)
 	} else {
 		err = -ESRCH;
 	}
+	release_sock(sk);
 
- destroy_err:
+destroy_err:
 	sock_put((struct sock *)msk);
 	return err;
 }
-- 
2.35.3