6.6-stable review patch. If anyone has any objections, please let me know.
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From: Kuniyuki Iwashima kuniyu@amazon.com
commit dcf70df2048d27c5d186f013f101a4aefd63aa41 upstream.
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 Signed-off-by: Lee Jones lee@kernel.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- include/net/af_unix.h | 1 + net/unix/af_unix.c | 2 +- net/unix/garbage.c | 20 +++++++++++++++++++- 3 files changed, 21 insertions(+), 2 deletions(-)
--- a/include/net/af_unix.h +++ b/include/net/af_unix.h @@ -24,6 +24,7 @@ void unix_inflight(struct user_struct *u void unix_notinflight(struct user_struct *user, struct file *fp); 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_prepare_fpl(struct scm_fp_list *fpl); void unix_destroy_fpl(struct scm_fp_list *fpl); void unix_gc(void); --- a/net/unix/af_unix.c +++ b/net/unix/af_unix.c @@ -1705,7 +1705,7 @@ static int unix_accept(struct socket *so }
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);
--- a/net/unix/garbage.c +++ b/net/unix/garbage.c @@ -101,6 +101,17 @@ struct unix_sock *unix_get_socket(struct return NULL; }
+static struct unix_vertex *unix_edge_successor(struct unix_edge *edge) +{ + /* If an embryo socket has a fd, + * the listener indirectly holds the fd's refcnt. + */ + if (edge->successor->listener) + return unix_sk(edge->successor->listener)->vertex; + + return edge->successor->vertex; +} + static LIST_HEAD(unix_unvisited_vertices);
enum unix_vertex_index { @@ -209,6 +220,13 @@ out: fpl->inflight = false; }
+void unix_update_edges(struct unix_sock *receiver) +{ + spin_lock(&unix_gc_lock); + receiver->listener = NULL; + spin_unlock(&unix_gc_lock); +} + int unix_prepare_fpl(struct scm_fp_list *fpl) { struct unix_vertex *vertex; @@ -268,7 +286,7 @@ next_vertex:
/* Explore neighbour vertices (receivers of the current vertex's fd). */ list_for_each_entry(edge, &vertex->edges, vertex_entry) { - struct unix_vertex *next_vertex = edge->successor->vertex; + struct unix_vertex *next_vertex = unix_edge_successor(edge);
if (!next_vertex) continue;