From dcf70df2048d27c5d186f013f101a4aefd63aa41 Mon Sep 17 00:00:00 2001
From: Kuniyuki Iwashima <kuniyu@amazon.com>
Date: Mon, 25 Mar 2024 13:24:18 -0700
Subject: af_unix: Fix up unix_edge.successor for embryo socket.
To garbage collect inflight AF_UNIX sockets, we must define the
cyclic reference appropriately. This is a bit tricky if the loop
consists of embryo sockets.
Suppose that the fd of AF_UNIX socket A is passed to D and the fd B
to C and that C and D are embryo sockets of A and B, respectively.
It may appear that there are two separate graphs, A (-> D) and
B (-> C), but this is not correct.
A --. .-- B
X
C <-' `-> D
Now, D holds A's refcount, and C has B's refcount, so unix_release()
will never be called for A and B when we close() them. However, no
one can call close() for D and C to free skbs holding refcounts of A
and B because C/D is in A/B's receive queue, which should have been
purged by unix_release() for A and B.
So, here's another type of cyclic reference. When a fd of an AF_UNIX
socket is passed to an embryo socket, the reference is indirectly held
by its parent listening socket.
.-> A .-> B
| `- sk_receive_queue | `- sk_receive_queue
| `- skb | `- skb
| `- sk == C | `- sk == D
| `- sk_receive_queue | `- sk_receive_queue
| `- skb +---------' `- skb +-.
| |
`---------------------------------------------------------'
Technically, the graph must be denoted as A <-> B instead of A (-> D)
and B (-> C) to find such a cyclic reference without touching each
socket's receive queue.
.-> A --. .-- B <-.
| X | == A <-> B
`-- C <-' `-> D --'
We apply this fixup during GC by fetching the real successor by
unix_edge_successor().
When we call accept(), we clear unix_sock.listener under unix_gc_lock
not to confuse GC.
Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Acked-by: Paolo Abeni <pabeni@redhat.com>
Link: https://lore.kernel.org/r/20240325202425.60930-9-kuniyu@amazon.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
---
net/unix/af_unix.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
(limited to 'net/unix/af_unix.c')
diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
index af74e7ebc35a..ae77e2dc0dae 100644
--- a/net/unix/af_unix.c
+++ b/net/unix/af_unix.c
@@ -1721,7 +1721,7 @@ static int unix_accept(struct socket *sock, struct socket *newsock, int flags,
}
tsk = skb->sk;
- unix_sk(tsk)->listener = NULL;
+ unix_update_edges(unix_sk(tsk));
skb_free_datagram(sk, skb);
wake_up_interruptible(&unix_sk(sk)->peer_wait);
--
cgit