From nobody Sun Feb 8 12:40:33 2026 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id A9DFF2206AC; Wed, 21 May 2025 15:34:03 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1747841643; cv=none; b=DzRG0F49+Egji0E0NW08oqraEPJ4n1dQ11RLBvPc99HHpaZEgut6TrWKYlEa7QzqqO1PTSwZfCHJazKE1Wh+99jcnWnPRTu+D3LDhjx2VOH92QLslRZXznIuZ9lkk58EgIjRjpdchIr6vh2l/iYuU6C5qxfVMY+bcYq5c7bTWMw= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1747841643; c=relaxed/simple; bh=eSfVZgrHS8VynzF1LFlvxACfI79Y+FAdwgbNMxCAqr4=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=g6MIwot9rImO+bQ7HZKwRv1gHiSu+8MntI40UGGfZ/7GS/oMOB86oBu8GL26Ay2sfg9/nWhvNiVR21jYyPwEpZoZc7xwRDxiIBb7TRdDbZXy+5RW6AzubyFpsK0ABcT1Lf4ZRZAK12NdPSrarWhokPCuoYh6ezDtfmNgFXrisHk= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=A1chswUg; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="A1chswUg" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 8A1EAC4CEE4; Wed, 21 May 2025 15:34:00 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1747841643; bh=eSfVZgrHS8VynzF1LFlvxACfI79Y+FAdwgbNMxCAqr4=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=A1chswUgNTH/Z4k/hLqCfpeiTQHBkTnA5bCOf20Eqv4/t1EETnCHW8VO8kL3VDhtW mBC79jmkest8lVadn6Gdm5GrOvSvpc4zAnSyODw1WNhnnxYXZGy6R48F5RNAaZCvaA GE8UVRtqR2IVH/IXBjenBv95RD+GoYNh5nBxXE4BxwfSeD4Hk9321RF37NYGfQtDck IYhOnUtcrHkmigDy952f1FUs6Vt9kS5pjaES23ThaasuvzxvNj7FrVaEGEH1PD0L2I 2wLRn4S4KiyMUTd/B9QwH5crYbTejxOcCl+VzkDhDrULTsloKBYBNnaS2YrLNMedjY qU0KiBFg3PDcg== From: Lee Jones To: lee@kernel.org, "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Christian Brauner , Kuniyuki Iwashima , Alexander Mikhalitsyn , Jens Axboe , Sasha Levin , Michal Luczaj , Rao Shoaib , Simon Horman , linux-kernel@vger.kernel.org, netdev@vger.kernel.org Cc: stable@vger.kernel.org Subject: [PATCH v6.1 15/27] af_unix: Fix up unix_edge.successor for embryo socket. Date: Wed, 21 May 2025 16:27:14 +0100 Message-ID: <20250521152920.1116756-16-lee@kernel.org> X-Mailer: git-send-email 2.49.0.1143.g0be31eac6b-goog In-Reply-To: <20250521152920.1116756-1-lee@kernel.org> References: <20250521152920.1116756-1-lee@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" From: Kuniyuki Iwashima [ Upstream commit dcf70df2048d27c5d186f013f101a4aefd63aa41 ] 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 =3D=3D C | `- sk =3D=3D 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 | =3D=3D 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 Acked-by: Paolo Abeni Link: https://lore.kernel.org/r/20240325202425.60930-9-kuniyu@amazon.com Signed-off-by: Jakub Kicinski (cherry picked from commit dcf70df2048d27c5d186f013f101a4aefd63aa41) Signed-off-by: Lee Jones --- include/net/af_unix.h | 1 + net/unix/af_unix.c | 2 +- net/unix/garbage.c | 20 +++++++++++++++++++- 3 files changed, 21 insertions(+), 2 deletions(-) diff --git a/include/net/af_unix.h b/include/net/af_unix.h index 624fea657518..d7f589e14467 100644 --- a/include/net/af_unix.h +++ b/include/net/af_unix.h @@ -24,6 +24,7 @@ void unix_inflight(struct user_struct *user, struct file = *fp); 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); diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c index 6075ecbe40b2..4d8b2b2b9a70 100644 --- a/net/unix/af_unix.c +++ b/net/unix/af_unix.c @@ -1679,7 +1679,7 @@ static int unix_accept(struct socket *sock, struct so= cket *newsock, int flags, } =20 tsk =3D skb->sk; - unix_sk(tsk)->listener =3D NULL; + unix_update_edges(unix_sk(tsk)); skb_free_datagram(sk, skb); wake_up_interruptible(&unix_sk(sk)->peer_wait); =20 diff --git a/net/unix/garbage.c b/net/unix/garbage.c index cdeff548e130..6ff7e0b5c544 100644 --- a/net/unix/garbage.c +++ b/net/unix/garbage.c @@ -101,6 +101,17 @@ struct unix_sock *unix_get_socket(struct file *filp) return NULL; } =20 +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); =20 enum unix_vertex_index { @@ -209,6 +220,13 @@ void unix_del_edges(struct scm_fp_list *fpl) fpl->inflight =3D false; } =20 +void unix_update_edges(struct unix_sock *receiver) +{ + spin_lock(&unix_gc_lock); + receiver->listener =3D NULL; + spin_unlock(&unix_gc_lock); +} + int unix_prepare_fpl(struct scm_fp_list *fpl) { struct unix_vertex *vertex; @@ -268,7 +286,7 @@ static void __unix_walk_scc(struct unix_vertex *vertex) =20 /* Explore neighbour vertices (receivers of the current vertex's fd). */ list_for_each_entry(edge, &vertex->edges, vertex_entry) { - struct unix_vertex *next_vertex =3D edge->successor->vertex; + struct unix_vertex *next_vertex =3D unix_edge_successor(edge); =20 if (!next_vertex) continue; --=20 2.49.0.1143.g0be31eac6b-goog