From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id B300BC433FE for ; Tue, 22 Nov 2022 20:58:43 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232419AbiKVU6m (ORCPT ); Tue, 22 Nov 2022 15:58:42 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:35452 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229628AbiKVU6k (ORCPT ); Tue, 22 Nov 2022 15:58:40 -0500 Received: from smtp-fw-33001.amazon.com (smtp-fw-33001.amazon.com [207.171.190.10]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id EAE025E3EF for ; Tue, 22 Nov 2022 12:58:38 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=amazon.com; i=@amazon.com; q=dns/txt; s=amazon201209; t=1669150719; x=1700686719; h=from:to:cc:subject:date:message-id:mime-version: content-transfer-encoding; bh=58dNQVKqeDksWseF0awQrKYpFQ4D7sUOyuz+r+YL5uk=; b=a02FxHO0HKXeurLPdII8dpbE5t0ZK9DJUGY3bviyPpJk1HY6ZUUL1H1x E9/xFGUAzE1i+800dBr3sGm3klYXdA+2PwdRYSd9D17e4EeBCBR7WzCNX 5jIeLqoNKN4384bi6LqlFvBl2bB+ymWtvfjJo8ZyO0GxssxJdHRwO+UcW w=; X-IronPort-AV: E=Sophos;i="5.96,185,1665446400"; d="scan'208";a="243003183" Received: from iad12-co-svc-p1-lb1-vlan3.amazon.com (HELO email-inbound-relay-iad-1d-m6i4x-25ac6bd5.us-east-1.amazon.com) ([10.43.8.6]) by smtp-border-fw-33001.sea14.amazon.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 22 Nov 2022 20:58:34 +0000 Received: from EX13MTAUWB002.ant.amazon.com (iad12-ws-svc-p26-lb9-vlan2.iad.amazon.com [10.40.163.34]) by email-inbound-relay-iad-1d-m6i4x-25ac6bd5.us-east-1.amazon.com (Postfix) with ESMTPS id 0539F42438; Tue, 22 Nov 2022 20:58:30 +0000 (UTC) Received: from EX19D004ANA001.ant.amazon.com (10.37.240.138) by EX13MTAUWB002.ant.amazon.com (10.43.161.202) with Microsoft SMTP Server (TLS) id 15.0.1497.42; Tue, 22 Nov 2022 20:58:29 +0000 Received: from 88665a182662.ant.amazon.com (10.43.161.14) by EX19D004ANA001.ant.amazon.com (10.37.240.138) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA) id 15.2.1118.20; Tue, 22 Nov 2022 20:58:27 +0000 From: Kuniyuki Iwashima To: "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni CC: Kuniyuki Iwashima , Kuniyuki Iwashima , , syzbot , Wei Chen Subject: [PATCH v1 net] af_unix: Call sk_diag_fill() under the bucket lock. Date: Tue, 22 Nov 2022 12:58:11 -0800 Message-ID: <20221122205811.20910-1-kuniyu@amazon.com> X-Mailer: git-send-email 2.30.2 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Content-Type: text/plain X-Originating-IP: [10.43.161.14] X-ClientProxiedBy: EX13D49UWC003.ant.amazon.com (10.43.162.10) To EX19D004ANA001.ant.amazon.com (10.37.240.138) Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org Wei Chen reported sk->sk_socket can be NULL in sk_user_ns(). [0][1] It seems that syzbot was dumping an AF_UNIX socket while closing it, and there is a race below. unix_release_sock unix_diag_handler_dump | `- unix_diag_get_exact | |- unix_lookup_by_ino | | |- spin_lock(&net->unx.table.locks[i]) | | |- sock_hold | | `- spin_unlock(&net->unx.table.locks[i]) |- unix_remove_socket(net, sk) | /* after releasing this lock, | /* from here, sk cannot be | * there is no guarantee that | * seen in the hash table. | * sk is not SOCK_DEAD. | */ | */ | | |- unix_state_lock(sk) | |- sock_orphan(sk) `- sk_diag_fill | |- sock_set_flag(sk, SOCK_DEAD) `- sk_diag_dump_uid | `- sk_set_socket(sk, NULL) `- sk_user_ns `- unix_state_unlock(sk) `- sk->sk_socket->file->f_cred->user_ns /* NULL deref here */ After releasing the bucket lock, we cannot guarantee that the found socket is still alive. Then, we have to check the SOCK_DEAD flag under unix_state_lock() and keep holding it unless we access the socket. In this case, however, we cannot acquire unix_state_lock() in unix_lookup_by_ino() because we lock it later in sk_diag_dump_peer(), resulting in deadlock. Instead, we do not release the bucket lock; then, we can safely access sk->sk_socket later in sk_user_ns(), and there is no deadlock scenario. We are already using this strategy in unix_diag_dump(). Note we have to call nlmsg_new() before unix_lookup_by_ino() not to change the flag from GFP_KERNEL to GFP_ATOMIC. [0]: https://lore.kernel.org/netdev/CAO4mrfdvyjFpokhNsiwZiP-wpdSD0AStcJwfKcKQdAALQ9_2Qw@mail.gmail.com/ [1]: BUG: kernel NULL pointer dereference, address: 0000000000000270 #PF: supervisor read access in kernel mode #PF: error_code(0x0000) - not-present page PGD 12bbce067 P4D 12bbce067 PUD 12bc40067 PMD 0 Oops: 0000 [#1] PREEMPT SMP CPU: 0 PID: 27942 Comm: syz-executor.0 Not tainted 6.1.0-rc5-next-20221118 #2 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.13.0-48-gd9c812dda519-prebuilt.qemu.org 04/01/2014 RIP: 0010:sk_user_ns include/net/sock.h:920 [inline] RIP: 0010:sk_diag_dump_uid net/unix/diag.c:119 [inline] RIP: 0010:sk_diag_fill+0x77d/0x890 net/unix/diag.c:170 Code: 89 ef e8 66 d4 2d fd c7 44 24 40 00 00 00 00 49 8d 7c 24 18 e8 54 d7 2d fd 49 8b 5c 24 18 48 8d bb 70 02 00 00 e8 43 d7 2d fd <48> 8b 9b 70 02 00 00 48 8d 7b 10 e8 33 d7 2d fd 48 8b 5b 10 48 8d RSP: 0018:ffffc90000d67968 EFLAGS: 00010246 RAX: ffff88812badaa48 RBX: 0000000000000000 RCX: ffffffff840d481d RDX: 0000000000000465 RSI: 0000000000000000 RDI: 0000000000000270 RBP: ffffc90000d679a8 R08: 0000000000000277 R09: 0000000000000000 R10: 0001ffffffffffff R11: 0001c90000d679a8 R12: ffff88812ac03800 R13: ffff88812c87c400 R14: ffff88812ae42210 R15: ffff888103026940 FS: 00007f08b4e6f700(0000) GS:ffff88813bc00000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 0000000000000270 CR3: 000000012c58b000 CR4: 00000000003506f0 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 Call Trace: unix_diag_get_exact net/unix/diag.c:285 [inline] unix_diag_handler_dump+0x3f9/0x500 net/unix/diag.c:317 __sock_diag_cmd net/core/sock_diag.c:235 [inline] sock_diag_rcv_msg+0x237/0x250 net/core/sock_diag.c:266 netlink_rcv_skb+0x13e/0x250 net/netlink/af_netlink.c:2564 sock_diag_rcv+0x24/0x40 net/core/sock_diag.c:277 netlink_unicast_kernel net/netlink/af_netlink.c:1330 [inline] netlink_unicast+0x5e9/0x6b0 net/netlink/af_netlink.c:1356 netlink_sendmsg+0x739/0x860 net/netlink/af_netlink.c:1932 sock_sendmsg_nosec net/socket.c:714 [inline] sock_sendmsg net/socket.c:734 [inline] ____sys_sendmsg+0x38f/0x500 net/socket.c:2476 ___sys_sendmsg net/socket.c:2530 [inline] __sys_sendmsg+0x197/0x230 net/socket.c:2559 __do_sys_sendmsg net/socket.c:2568 [inline] __se_sys_sendmsg net/socket.c:2566 [inline] __x64_sys_sendmsg+0x42/0x50 net/socket.c:2566 do_syscall_x64 arch/x86/entry/common.c:50 [inline] do_syscall_64+0x2b/0x70 arch/x86/entry/common.c:80 entry_SYSCALL_64_after_hwframe+0x63/0xcd RIP: 0033:0x4697f9 Code: f7 d8 64 89 02 b8 ff ff ff ff c3 66 0f 1f 44 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 bc ff ff ff f7 d8 64 89 01 48 RSP: 002b:00007f08b4e6ec48 EFLAGS: 00000246 ORIG_RAX: 000000000000002e RAX: ffffffffffffffda RBX: 000000000077bf80 RCX: 00000000004697f9 RDX: 0000000000000000 RSI: 00000000200001c0 RDI: 0000000000000003 RBP: 00000000004d29e9 R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000246 R12: 000000000077bf80 R13: 0000000000000000 R14: 000000000077bf80 R15: 00007ffdb36bc6c0 Modules linked in: CR2: 0000000000000270 Fixes: 5d3cae8bc39d ("unix_diag: Dumping exact socket core") Reported-by: syzbot Reported-by: Wei Chen Signed-off-by: Kuniyuki Iwashima --- net/unix/diag.c | 38 +++++++++++++++++++++++--------------- 1 file changed, 23 insertions(+), 15 deletions(-) diff --git a/net/unix/diag.c b/net/unix/diag.c index 105f522a89fe..96583cb71cf5 100644 --- a/net/unix/diag.c +++ b/net/unix/diag.c @@ -242,8 +242,9 @@ static struct sock *unix_lookup_by_ino(struct net *net, unsigned int ino) spin_lock(&net->unx.table.locks[i]); sk_for_each(sk, &net->unx.table.buckets[i]) { if (ino == sock_i_ino(sk)) { - sock_hold(sk); - spin_unlock(&net->unx.table.locks[i]); + /* sk_diag_fill() must be done under the bucket + * lock not to race with unix_release_sock(). + */ return sk; } } @@ -264,15 +265,6 @@ static int unix_diag_get_exact(struct sk_buff *in_skb, err = -EINVAL; if (req->udiag_ino == 0) - goto out_nosk; - - sk = unix_lookup_by_ino(net, req->udiag_ino); - err = -ENOENT; - if (sk == NULL) - goto out_nosk; - - err = sock_diag_check_cookie(sk, req->udiag_cookie); - if (err) goto out; extra_len = 256; @@ -282,8 +274,21 @@ static int unix_diag_get_exact(struct sk_buff *in_skb, if (!rep) goto out; + /* Acquire a bucket lock on success. */ + sk = unix_lookup_by_ino(net, req->udiag_ino); + err = -ENOENT; + if (!sk) + goto free; + + err = sock_diag_check_cookie(sk, req->udiag_cookie); + if (err) + goto unlock; + err = sk_diag_fill(sk, rep, req, NETLINK_CB(in_skb).portid, nlh->nlmsg_seq, 0, req->udiag_ino); + + spin_unlock(&net->unx.table.locks[sk->sk_hash]); + if (err < 0) { nlmsg_free(rep); extra_len += 256; @@ -292,13 +297,16 @@ static int unix_diag_get_exact(struct sk_buff *in_skb, goto again; } - err = nlmsg_unicast(net->diag_nlsk, rep, NETLINK_CB(in_skb).portid); + err = nlmsg_unicast(net->diag_nlsk, rep, NETLINK_CB(in_skb).portid); out: - if (sk) - sock_put(sk); -out_nosk: return err; + +unlock: + spin_unlock(&net->unx.table.locks[sk->sk_hash]); +free: + nlmsg_free(rep); + goto out; } static int unix_diag_handler_dump(struct sk_buff *skb, struct nlmsghdr *h) -- 2.30.2