From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from lindbergh.monkeyblade.net (lindbergh.monkeyblade.net [23.128.96.19]) (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 76477134B0; Thu, 31 Aug 2023 15:24:23 +0000 (UTC) Received: from szxga02-in.huawei.com (szxga02-in.huawei.com [45.249.212.188]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id D1B03E6E; Thu, 31 Aug 2023 08:23:50 -0700 (PDT) Received: from kwepemd100003.china.huawei.com (unknown [172.30.72.56]) by szxga02-in.huawei.com (SkyGuard) with ESMTP id 4Rc4cm5DRgzVkLy; Thu, 31 Aug 2023 23:21:12 +0800 (CST) Received: from [10.67.111.192] (10.67.111.192) by kwepemd100003.china.huawei.com (7.221.188.180) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.2.1258.23; Thu, 31 Aug 2023 23:23:39 +0800 Message-ID: <1c533412-b192-3868-991a-d35587329803@huawei.com> Date: Thu, 31 Aug 2023 23:23:38 +0800 Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:91.0) Gecko/20100101 Thunderbird/91.9.0 Subject: Re: [BUG bpf-next] bpf/net: Hitting gpf when running selftests Content-Language: en-US From: Xu Kuohai To: Jiri Olsa CC: Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , , , Martin KaFai Lau , Song Liu , Yonghong Song , John Fastabend , KP Singh , Stanislav Fomichev , Hao Luo , Hou Tao , Bobby Eshleman References: <23cd4ce0-0360-e3c6-6cc9-f597aefb2ab5@huawei.com> In-Reply-To: <23cd4ce0-0360-e3c6-6cc9-f597aefb2ab5@huawei.com> Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 8bit X-Originating-IP: [10.67.111.192] X-ClientProxiedBy: dggems703-chm.china.huawei.com (10.3.19.180) To kwepemd100003.china.huawei.com (7.221.188.180) X-CFilter-Loop: Reflected X-Spam-Status: No, score=-7.7 required=5.0 tests=BAYES_00,NICE_REPLY_A, RCVD_IN_DNSWL_MED,RCVD_IN_MSPIKE_H5,RCVD_IN_MSPIKE_WL,SPF_HELO_NONE, SPF_PASS autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net On 8/31/2023 5:46 PM, Xu Kuohai wrote: > On 8/31/2023 5:07 AM, Jiri Olsa wrote: >> On Wed, Aug 30, 2023 at 08:58:11PM +0200, Jiri Olsa wrote: >>> hi, >>> I'm hitting crash below on bpf-next/master when running selftests, >>> full log and config attached >> >> it seems to be 'test_progs -t sockmap_listen' triggering that >> >> jirka >> >>> >>> jirka >>> >>> >>> --- >>> [ 1022.710250][ T2556] general protection fault, probably for non-canonical address 0x6b6b6b6b6b6b6b73: 0000 [#1] PREEMPT SMP DEBUG_PAGEALLOC NOPTI^M >>> [ 1022.711206][ T2556] CPU: 2 PID: 2556 Comm: kworker/2:4 Tainted: G           OE      6.5.0+ #693 1723c8b9805ff5a1672ab7e6f25977078a7bcceb^M >>> [ 1022.712120][ T2556] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.2-1.fc38 04/01/2014^M >>> [ 1022.712830][ T2556] Workqueue: events sk_psock_backlog^M >>> [ 1022.713262][ T2556] RIP: 0010:skb_dequeue+0x4c/0x80^M >>> [ 1022.713653][ T2556] Code: 41 48 85 ed 74 3c 8b 43 10 4c 89 e7 83 e8 01 89 43 10 48 8b 45 08 48 8b 55 00 48 c7 45 08 00 00 00 00 48 c7 45 00 00 00 00 00 <48> 89 42 08 48 89 10 e8 e8 6a 41 00 48 89 e8 5b 5d 41 5c c3 cc cc^M >>> [ 1022.714963][ T2556] RSP: 0018:ffffc90003ca7dd0 EFLAGS: 00010046^M >>> [ 1022.715431][ T2556] RAX: 6b6b6b6b6b6b6b6b RBX: ffff88811de269d0 RCX: 0000000000000000^M >>> [ 1022.716068][ T2556] RDX: 6b6b6b6b6b6b6b6b RSI: 0000000000000282 RDI: ffff88811de269e8^M >>> [ 1022.716676][ T2556] RBP: ffff888141ae39c0 R08: 0000000000000001 R09: 0000000000000000^M >>> [ 1022.717283][ T2556] R10: 0000000000000001 R11: 0000000000000000 R12: ffff88811de269e8^M >>> [ 1022.717930][ T2556] R13: 0000000000000001 R14: ffff888141ae39c0 R15: ffff88810a20e640^M >>> [ 1022.718549][ T2556] FS:  0000000000000000(0000) GS:ffff88846d600000(0000) knlGS:0000000000000000^M >>> [ 1022.719241][ T2556] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033^M >>> [ 1022.719761][ T2556] CR2: 00007fb5c25ca000 CR3: 000000012b902004 CR4: 0000000000770ee0^M >>> [ 1022.720394][ T2556] PKRU: 55555554^M >>> [ 1022.720699][ T2556] Call Trace:^M >>> [ 1022.720984][ T2556]  ^M >>> [ 1022.721254][ T2556]  ? die_addr+0x32/0x80^M >>> [ 1022.721589][ T2556]  ? exc_general_protection+0x25a/0x4b0^M >>> [ 1022.722026][ T2556]  ? asm_exc_general_protection+0x22/0x30^M >>> [ 1022.722489][ T2556]  ? skb_dequeue+0x4c/0x80^M >>> [ 1022.722854][ T2556]  sk_psock_backlog+0x27a/0x300^M >>> [ 1022.723243][ T2556]  process_one_work+0x2a7/0x5b0^M >>> [ 1022.723633][ T2556]  worker_thread+0x4f/0x3a0^M >>> [ 1022.723998][ T2556]  ? __pfx_worker_thread+0x10/0x10^M >>> [ 1022.724386][ T2556]  kthread+0xfd/0x130^M >>> [ 1022.724709][ T2556]  ? __pfx_kthread+0x10/0x10^M >>> [ 1022.725066][ T2556]  ret_from_fork+0x2d/0x50^M >>> [ 1022.725409][ T2556]  ? __pfx_kthread+0x10/0x10^M >>> [ 1022.725799][ T2556]  ret_from_fork_asm+0x1b/0x30^M >>> [ 1022.726201][ T2556]  ^M >> >> >> . > > My patch failed on the BPF CI, and the log shows the test also died in skb_dequeue: > > https://github.com/kernel-patches/bpf/actions/runs/6031993528/job/16366782122 > > [...] > >   [   74.396478]  ? __die_body+0x1f/0x70 >   [   74.396700]  ? page_fault_oops+0x15b/0x450 >   [   74.396957]  ? fixup_exception+0x26/0x330 >   [   74.397211]  ? exc_page_fault+0x68/0x1a0 >   [   74.397457]  ? asm_exc_page_fault+0x26/0x30 >   [   74.397724]  ? skb_dequeue+0x52/0x90 >   [   74.397954]  sk_psock_destroy+0x8c/0x2b0 >   [   74.398204]  process_one_work+0x28a/0x550 >   [   74.398458]  ? __pfx_worker_thread+0x10/0x10 >   [   74.398730]  worker_thread+0x51/0x3c0 >   [   74.398966]  ? __pfx_worker_thread+0x10/0x10 >   [   74.399235]  kthread+0xf7/0x130 >   [   74.399437]  ? __pfx_kthread+0x10/0x10 >   [   74.399707]  ret_from_fork+0x34/0x50 >   [   74.399967]  ? __pfx_kthread+0x10/0x10 >   [   74.400234]  ret_from_fork_asm+0x1b/0x30 > > > After a few tries, I found a way to reproduce the problem. > > Here is the reproduce steps: > > 1. create a kprobe to delay sk_psock_backlog: > > static struct kprobe kp = { >         .symbol_name = "sk_psock_backlog", >         .offset = 0x00, > }; > > static int handler_pre(struct kprobe *p, struct pt_regs *regs) > { >         mdelay(1000); >         return 0; > } > > static int __init kprobe_init(void) > { >         int ret; > >         kp.pre_handler = handler_pre; > >         ret = register_kprobe(&kp); >         if (ret < 0) { >                 return -1; >         } > >         return 0; > } > > 2. insert the kprobe and run the vsock sockmap test: > > ./test_progs -t "sockmap_listen/sockmap VSOCK test_vsock_redir" > > > > I guess the problem is in sk_psock_backlog, where skb is inserted to another > list before skb_dequeue is called. > > So I tested it with the following changes, and found the problem did go away. > > --- a/net/core/skmsg.c > +++ b/net/core/skmsg.c > @@ -648,7 +648,7 @@ static void sk_psock_backlog(struct work_struct *work) >                 off = state->off; >         } > > -       while ((skb = skb_peek(&psock->ingress_skb))) { > +       while ((skb = skb_dequeue(&psock->ingress_skb))) { >                 len = skb->len; >                 off = 0; >                 if (skb_bpf_strparser(skb)) { > @@ -684,7 +684,6 @@ static void sk_psock_backlog(struct work_struct *work) >                         len -= ret; >                 } while (len); > > -               skb = skb_dequeue(&psock->ingress_skb); >                 if (!ingress) { >                         kfree_skb(skb); >                 } > > Not clear what exactly happened, needs more debugging. > Use the skb address obtained from skb_peek() in sk_psock_backlog() as the key, 4 stack traces are obtained. trace 0, the skb is queued to the target socket ingress queue: [ 120.042016] sk_psock_skb_ingress_enqueue+0xf5/0x160 [ 120.045052] sk_psock_backlog+0x206/0x400 [ 120.047366] process_one_work+0x292/0x560 [ 120.049657] worker_thread+0x53/0x3e0 [ 120.051698] kthread+0x102/0x130 [ 120.053497] ret_from_fork+0x34/0x50 [ 120.055528] ret_from_fork_asm+0x1b/0x30 trace 1, the skb is consumed by the user: [ 120.061537] consume_skb+0x47/0x100 [ 120.063394] sk_msg_recvmsg+0x268/0x3e0 [ 120.065458] unix_bpf_recvmsg+0x16c/0x610 [ 120.067584] unix_stream_recvmsg+0x66/0xa0 [ 120.069946] sock_recvmsg+0xc4/0xd0 [ 120.072063] __sys_recvfrom+0xaf/0x120 [ 120.073933] __x64_sys_recvfrom+0x29/0x30 [ 120.076052] do_syscall_64+0x3f/0x90 [ 120.077986] entry_SYSCALL_64_after_hwframe+0x6e/0xd8 trace 2, the vsock socket is closed by the user, and a new skb with the same address is allocated in vsock_release: [ 120.084296] __alloc_skb+0xe3/0x180 [ 120.086335] virtio_transport_alloc_skb+0x3b/0x2c0 [ 120.089174] virtio_transport_send_pkt_info+0x118/0x230 [ 120.092191] virtio_transport_release+0x29d/0x400 [ 120.094845] __vsock_release+0x3c/0x1e0 [ 120.096905] vsock_release+0x18/0x30 [ 120.098899] __sock_release+0x3d/0xc0 [ 120.100885] sock_close+0x18/0x20 [ 120.102606] __fput+0x108/0x2b0 [ 120.104636] task_work_run+0x5d/0xa0 [ 120.106876] exit_to_user_mode_prepare+0x18c/0x190 [ 120.109619] syscall_exit_to_user_mode+0x1d/0x50 [ 120.112049] do_syscall_64+0x4c/0x90 [ 120.114115] entry_SYSCALL_64_after_hwframe+0x6e/0xd8 trace 3, sk_psock_backlog() calls skb_dequeue() to unlink the skb, since this skb is now actually a new skb allocated in vsock_release, its prev and next fields are both set to NULL, NULL deref occurs. [ 120.120619] skb_dequeue+0x92/0xa0 [ 120.122350] sk_psock_backlog+0x305/0x400 [ 120.124512] process_one_work+0x292/0x560 [ 120.126771] worker_thread+0x53/0x3e0 [ 120.128843] kthread+0x102/0x130 [ 120.130772] ret_from_fork+0x34/0x50 To fix it, it seems reasonable to replace skb_peek() with skb_dequeue() in sk_psock_backlog(), since we can't prevent the skb from being appended to an ingress queue and consumed by user, as shown in trace 1 and trace 2.