netdev - [PATCH net 1/4] net: mctp: add an explicit reference from a mctp_sk

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Date:   Tue, 24 Jan 2023 10:01:03 +0800
From:   Jeremy Kerr <jk@...econstruct.com.au>
To:     netdev@...r.kernel.org
Cc:     Matt Johnston <matt@...econstruct.com.au>,
        Paolo Abeni <pabeni@...hat.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Noam Rathaus <noamr@...-disclosure.com>
Subject: [PATCH net 1/4] net: mctp: add an explicit reference from a mctp_sk_key to sock

Currently, we correlate the mctp_sk_key lifetime to the sock lifetime
through the sock hash/unhash operations, but this is pretty tenuous, and
there are cases where we may have a temporary reference to an unhashed
sk.

This change makes the reference more explicit, by adding a hold on the
sock when it's associated with a mctp_sk_key, released on final key
unref.

Fixes: 73c618456dc5 ("mctp: locking, lifetime and validity changes for sk_keys")
Signed-off-by: Jeremy Kerr <jk@...econstruct.com.au>
---
 net/mctp/route.c | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/net/mctp/route.c b/net/mctp/route.c
index f9a80b82dc51..ce10ba7ae839 100644
--- a/net/mctp/route.c
+++ b/net/mctp/route.c
@@ -147,6 +147,7 @@ static struct mctp_sk_key *mctp_key_alloc(struct mctp_sock *msk,
 	key->valid = true;
 	spin_lock_init(&key->lock);
 	refcount_set(&key->refs, 1);
+	sock_hold(key->sk);
 
 	return key;
 }
@@ -165,6 +166,7 @@ void mctp_key_unref(struct mctp_sk_key *key)
 	mctp_dev_release_key(key->dev, key);
 	spin_unlock_irqrestore(&key->lock, flags);
 
+	sock_put(key->sk);
 	kfree(key);
 }
 
@@ -419,14 +421,14 @@ static int mctp_route_input(struct mctp_route *route, struct sk_buff *skb)
 			 * this function.
 			 */
 			rc = mctp_key_add(key, msk);
-			if (rc) {
-				kfree(key);
-			} else {
+			if (!rc)
 				trace_mctp_key_acquire(key);
 
-				/* we don't need to release key->lock on exit */
-				mctp_key_unref(key);
-			}
+			/* we don't need to release key->lock on exit, so
+			 * clean up here and suppress the unlock via
+			 * setting to NULL
+			 */
+			mctp_key_unref(key);
 			key = NULL;
 
 		} else {
-- 
2.35.1