From owner-freebsd-net@freebsd.org Fri Jan 8 17:17:39 2021 Return-Path: Delivered-To: freebsd-net@mailman.nyi.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2610:1c1:1:606c::19:1]) by mailman.nyi.freebsd.org (Postfix) with ESMTP id 6EEF94D0043 for ; Fri, 8 Jan 2021 17:17:39 +0000 (UTC) (envelope-from shamaz.mazum@gmail.com) Received: from mail-oi1-x229.google.com (mail-oi1-x229.google.com [IPv6:2607:f8b0:4864:20::229]) (using TLSv1.3 with cipher TLS_AES_128_GCM_SHA256 (128/128 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256 client-signature RSA-PSS (2048 bits) client-digest SHA256) (Client CN "smtp.gmail.com", Issuer "GTS CA 1O1" (verified OK)) by mx1.freebsd.org (Postfix) with ESMTPS id 4DC8tV5J10z4fwC; Fri, 8 Jan 2021 17:17:38 +0000 (UTC) (envelope-from shamaz.mazum@gmail.com) Received: by mail-oi1-x229.google.com with SMTP id l200so12067574oig.9; Fri, 08 Jan 2021 09:17:38 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc:content-transfer-encoding; bh=U1XULY60lULrhC6AYk5yykBHgawQJqooBllHjETh2pQ=; b=MHBzqhpmqZVIhB7KiVtZAj1K3QPECyybTXWcc28IunvA2TGyotcKmwDPyfHkxy85+R KYbzaeDQff5naJOs51uvCd6zqJU4OSTrV5NpEMGYbh6hp//vFXVeSAP6FYGT+J7RKJX7 KByYZNAqK+miMddEDgMvzhjzsaa43Uwgjic8KHWqqHTsoA8q1wrDBWyORNQbtxtzxgWa mAvSNMQF9K8LoWKXc3f90z0JoHQaopdobIAjit5TzTsM0xgpG0j7n6j4V3WKgja3up+G VIjvO0ZIzDq4HSjJ0oHAn9XHv1LqnovPzpPD78M33KE0HeSTjlAWlPGCufvhbD3XzdL5 rvmA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc:content-transfer-encoding; bh=U1XULY60lULrhC6AYk5yykBHgawQJqooBllHjETh2pQ=; b=CtpDLtR/7XLyICqlM8mfe6yno9mQkaAe6fnfSBEOzR+daqnaCDNM8Ekx9IVqExYSFK gAUpskI8t46XT8KeIUcMUdRoGbRpNKHbPDVgqaqzUuUWAwJ11FjGAyjEmg5PadR7OuiL OLltExU72auhNwcFbq1CjuCSywUGrZvjC26nYStCGpQWhcAsyROOT9f7icqvoTn29o/Y GxDJKqtnH7fjvko5OAc250IXLBUcd6tr7BwvAeX/6knM4/gfy92fr/Jdv7z5N8VB6xBR qYQAN7GWosW/o7m9I9oJ0mYOdVHgMDaH0e/WdQuqvGBiV0rILahk21YyEoVc0/azNMk6 SbVA== X-Gm-Message-State: AOAM530eCWz0yL6yeHvzXN5LbRJvaMujuCtyTk+hESBJ0eB3Jqul0Mp7 1kav7OOFzo48n1api0g5Nqn9Y+VIUaoh01b0AZKZAV0rSx2roQ== X-Google-Smtp-Source: ABdhPJw1FGPMKZt81iBncu3MiIlClEWCQhKOYPx/iTDtKpCICjhykVUI7BfVwarG7GyqpTSkk5lMa6PtzRSzJa+mjMI= X-Received: by 2002:aca:5653:: with SMTP id k80mr3037330oib.0.1610126257266; Fri, 08 Jan 2021 09:17:37 -0800 (PST) MIME-Version: 1.0 References: In-Reply-To: From: Vasily Postnicov Date: Fri, 8 Jan 2021 20:17:25 +0300 Message-ID: Subject: Re: DNS using Name Service Switch module and Casper To: Mark Johnston Cc: freebsd-net@freebsd.org Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Queue-Id: 4DC8tV5J10z4fwC X-Spamd-Bar: - Authentication-Results: mx1.freebsd.org; dkim=pass header.d=gmail.com header.s=20161025 header.b=MHBzqhpm; dmarc=pass (policy=none) header.from=gmail.com; spf=pass (mx1.freebsd.org: domain of shamazmazum@gmail.com designates 2607:f8b0:4864:20::229 as permitted sender) smtp.mailfrom=shamazmazum@gmail.com X-Spamd-Result: default: False [-1.59 / 15.00]; TO_DN_SOME(0.00)[]; FREEMAIL_FROM(0.00)[gmail.com]; R_SPF_ALLOW(-0.20)[+ip6:2607:f8b0:4000::/36]; DKIM_TRACE(0.00)[gmail.com:+]; RCPT_COUNT_TWO(0.00)[2]; DMARC_POLICY_ALLOW(-0.50)[gmail.com,none]; NEURAL_HAM_SHORT(-0.59)[-0.587]; FROM_EQ_ENVFROM(0.00)[]; MIME_TRACE(0.00)[0:+]; RBL_DBL_DONT_QUERY_IPS(0.00)[2607:f8b0:4864:20::229:from]; FREEMAIL_ENVFROM(0.00)[gmail.com]; ASN(0.00)[asn:15169, ipnet:2607:f8b0::/32, country:US]; TAGGED_FROM(0.00)[]; DWL_DNSWL_NONE(0.00)[gmail.com:dkim]; ARC_NA(0.00)[]; NEURAL_HAM_MEDIUM(-1.00)[-1.000]; R_DKIM_ALLOW(-0.20)[gmail.com:s=20161025]; FROM_HAS_DN(0.00)[]; TO_MATCH_ENVRCPT_ALL(0.00)[]; MIME_GOOD(-0.10)[text/plain]; SPAMHAUS_ZRD(0.00)[2607:f8b0:4864:20::229:from:127.0.2.255]; NEURAL_SPAM_LONG(1.00)[1.000]; RCVD_IN_DNSWL_NONE(0.00)[2607:f8b0:4864:20::229:from]; RCVD_COUNT_TWO(0.00)[2]; RCVD_TLS_ALL(0.00)[]; MAILMAN_DEST(0.00)[freebsd-net] X-BeenThere: freebsd-net@freebsd.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: Networking and TCP/IP with FreeBSD List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 08 Jan 2021 17:17:39 -0000 I have noticed that after I kill stuck ping, the process spawned with cap_init() remains. I cannot even kill it with SIGKILL. This is the output of procstat on such a process. vasily 969 0.0 0.1 26428 6532 v0 I 22:43 0:00.00 ping vonbraun.local vasily 983 0.0 0.1 26428 6532 v0 I 22:43 0:00.00 ping resurrected.local vasily 1024 0.0 0.1 26428 6532 v0 I 22:49 0:00.00 ping resurrected.local vasily 1028 0.0 0.1 26428 6532 v0 I 22:49 0:00.00 ping resurrected.local root 1089 0.0 0.0 12976 2512 v1 S+ 22:58 0:00.01 grep ping PID TID COMM TDNAME KSTACK 1028 100579 ping - mi_switch+0x155 sleepq_switch+0x109 sleepq_catch_signals+0x266 sleepq_wait_sig+0x9 _sleep+0x2aa umtxq_sleep+0x19e do_lock_umutex+0x744 __umtx_op_wait_umutex+0x49 sys__umtx_op+0x7a amd64_syscall+0x12e fast_syscall_common+0xf8 I checked ZeroMQ on which my NSS module is based. It does not use pthread_atfork(), but uses lots of other unusual pthread functions, like pthread_setaffinity_np() or pthread_setschedparam(). Do not know if it matters. Also I do not quite understand when the code in my module is executed. It should be executed after the capsicumized sandbox is created, should it not? And I got hang in the process of creating the sandbox. So I do not understand how my code affects this process :) =D0=BF=D1=82, 8 =D1=8F=D0=BD=D0=B2. 2021 =D0=B3. =D0=B2 18:45, Mark Johnsto= n : > > On Wed, Jan 06, 2021 at 07:08:14PM +0300, Vasily Postnicov wrote: > > That's what I found. > > > > At first, ping calls cap_init() in capdns_setup(). cap_init() forks a > > process, then the parent returns and the child calls casper_main_loop()= . > > The child and the parent both have a socket to communicate. > > casper_main_loop() calls zygote_init() and that one blocks on fork(). I= do > > not know how it could be. How can fork() block? > > Does you module somehow use pthread_atfork()? > > > The parent process later calls cap_service_open() and that function cal= ls > > cap_xfer_nvlist(). Because the child process is stuck somewhere in > > zygote_init() it never sends an nvlist back. So ping blocks. > > Can you show output from "procstat -kk " when this hang occurs? > > > All this is figured out by inserting printf()'s. LLDB refuses to run pi= ng > > with 'error: Child exec failed'. > > Presumably it needs to be run as root since ping(8) is a setuid > executable. > > > =D0=B2=D1=82, 5 =D1=8F=D0=BD=D0=B2. 2021 =D0=B3. =D0=B2 17:43, Mark Joh= nston : > > > > > On Tue, Jan 05, 2021 at 10:02:37AM +0300, Vasily Postnicov wrote: > > > > Hello. I wrote a simple daemon called ZeroDNS which provides > > > functionality > > > > similar to multicast DNS, namely it discovers other participating > > > machines > > > > over the LAN and stores their hostname and IPv4 address pairs. > > > > > > > > Here is a NSS module which allows the system to use information fro= m that > > > > daemon: > > > > https://github.com/shamazmazum/nss-zero-dns > > > > > > > > You need to modify /etc/nsswitch.conf, changing the line 'hosts: fi= les > > > dns' > > > > to 'hosts: files dns zerodns'. > > > > > > > > It all works on FreeBSD 12.2-RELEASE, but sometimes not on 13.0-CUR= RENT. > > > > For example, ping(8) just blocks when trying to ping a host whose n= ame is > > > > resolvable with ZeroDNS. Turns out that programs built with casper > > > support > > > > (like ping(8) and some others) stop working with my NSS module (the= y just > > > > block trying to resolve the name). > > > > > > Presumably it's the casper process (i.e., cap_dns) that uses your > > > module? If the main ping process is blocked trying to resolve a name= , > > > it's waiting for the cap_dns process - where exactly is it getting > > > stuck? > > > > > > > Is there some kind of manual on how to write casper-compatible NSS > > > modules? > > >