[PATCH v1 net-next 05/16] af_unix: Fix up unix_edge.successor for embryo socket.
From: Kuniyuki Iwashima <hidden>
Date: 2024-02-03 03:03:18
Subsystem:
networking [general], networking [unix sockets], the rest · Maintainers:
"David S. Miller", Eric Dumazet, Jakub Kicinski, Paolo Abeni, Kuniyuki Iwashima, Linus Torvalds
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 a new 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 in unix_add_edges() if the receiver is an embryo
socket.
We also link such edges to the embryo socket because we need
to restore the original separte graphs A (-> D) and B (-> C) in
unix_update_edges() once accept() is called.
Signed-off-by: Kuniyuki Iwashima <redacted>
---
include/net/af_unix.h | 2 ++
net/unix/af_unix.c | 2 +-
net/unix/garbage.c | 29 ++++++++++++++++++++++++++++-
3 files changed, 31 insertions(+), 2 deletions(-)
diff --git a/include/net/af_unix.h b/include/net/af_unix.h
index 438d2a18ba2e..2d8e93775e61 100644
--- a/include/net/af_unix.h
+++ b/include/net/af_unix.h@@ -25,6 +25,7 @@ void unix_notinflight(struct user_struct *user, struct file *fp); void unix_init_vertex(struct unix_sock *u); void unix_add_edges(struct scm_fp_list *fpl, struct unix_sock *receiver); void unix_del_edges(struct scm_fp_list *fpl); +void unix_update_edges(struct unix_sock *receiver); int unix_alloc_edges(struct scm_fp_list *fpl); void unix_free_edges(struct scm_fp_list *fpl); void unix_gc(void);
@@ -40,6 +41,7 @@ struct unix_edge { struct unix_vertex *predecessor; struct unix_vertex *successor; struct list_head entry; + struct list_head embryo_entry; }; struct sock *unix_peer_get(struct sock *sk);
diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
index 1ebc3c15f972..dab5d8d96e87 100644
--- a/net/unix/af_unix.c
+++ b/net/unix/af_unix.c@@ -1734,7 +1734,7 @@ 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);
diff --git a/net/unix/garbage.c b/net/unix/garbage.c
index 572ac0994c69..d731438d3c2b 100644
--- a/net/unix/garbage.c
+++ b/net/unix/garbage.c@@ -115,10 +115,16 @@ static LIST_HEAD(unix_unvisited_vertices); void unix_add_edges(struct scm_fp_list *fpl, struct unix_sock *receiver) { + struct unix_vertex *successor; int i = 0, j = 0; spin_lock(&unix_gc_lock); + if (receiver->listener) + successor = &unix_sk(receiver->listener)->vertex; + else + successor = &receiver->vertex; + while (i < fpl->count_unix) { struct unix_sock *inflight = unix_get_socket(fpl->fp[j++]); struct unix_edge *edge;
@@ -128,13 +134,18 @@ void unix_add_edges(struct scm_fp_list *fpl, struct unix_sock *receiver) edge = fpl->edges + i++; edge->predecessor = &inflight->vertex; - edge->successor = &receiver->vertex; + edge->successor = successor; if (!edge->predecessor->out_degree++) list_add_tail(&edge->predecessor->entry, &unix_unvisited_vertices); INIT_LIST_HEAD(&edge->entry); list_add_tail(&edge->entry, &edge->predecessor->edges); + + if (receiver->listener) { + INIT_LIST_HEAD(&edge->embryo_entry); + list_add_tail(&edge->embryo_entry, &receiver->vertex.edges); + } } spin_unlock(&unix_gc_lock);
@@ -162,6 +173,22 @@ void unix_del_edges(struct scm_fp_list *fpl) fpl->inflight = false; } +void unix_update_edges(struct unix_sock *receiver) +{ + struct unix_edge *edge; + + spin_lock(&unix_gc_lock); + + list_for_each_entry(edge, &receiver->vertex.edges, embryo_entry) + edge->successor = &receiver->vertex; + + list_del_init(&receiver->vertex.edges); + + receiver->listener = NULL; + + spin_unlock(&unix_gc_lock); +} + int unix_alloc_edges(struct scm_fp_list *fpl) { if (!fpl->count_unix)
--
2.30.2