netdev - [PATCH net 1/2] rxrpc: Fix local endpoint replacement

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Date:   Wed, 14 Aug 2019 11:47:58 +0100
From:   David Howells <dhowells@...hat.com>
To:     netdev@...r.kernel.org
Cc:     dhowells@...hat.com, linux-afs@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH net 1/2] rxrpc: Fix local endpoint replacement

When a local endpoint (struct rxrpc_local) ceases to be in use by any
AF_RXRPC sockets, it starts the process of being destroyed, but this
doesn't cause it to be removed from the namespace endpoint list immediately
as tearing it down isn't trivial and can't be done in softirq context, so
it gets deferred.

If a new socket comes along that wants to bind to the same endpoint, a new
rxrpc_local object will be allocated and rxrpc_lookup_local() will use
list_replace() to substitute the new one for the old.

Then, when the dying object gets to rxrpc_local_destroyer(), it is removed
unconditionally from whatever list it is on by calling list_del_init().

However, list_replace() doesn't reset the pointers in the replaced
list_head and so the list_del_init() will likely corrupt the local
endpoints list.

Fix this by using list_replace_init() instead.

Fixes: 730c5fd42c1e ("rxrpc: Fix local endpoint refcounting")
Reported-by: syzbot+193e29e9387ea5837f1d@...kaller.appspotmail.com
Signed-off-by: David Howells <dhowells@...hat.com>
---

 net/rxrpc/local_object.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/rxrpc/local_object.c b/net/rxrpc/local_object.c
index c9db3e762d8d..c45765b7263e 100644
--- a/net/rxrpc/local_object.c
+++ b/net/rxrpc/local_object.c
@@ -283,7 +283,7 @@ struct rxrpc_local *rxrpc_lookup_local(struct net *net,
 		goto sock_error;

 	if (cursor != &rxnet->local_endpoints)
-		list_replace(cursor, &local->link);
+		list_replace_init(cursor, &local->link);
 	else
 		list_add_tail(&local->link, cursor);
 	age = "new";