Date: Fri, 8 Jan 2021 20:17:25 +0300 From: Vasily Postnicov <shamaz.mazum@gmail.com> To: Mark Johnston <markj@freebsd.org> Cc: freebsd-net@freebsd.org Subject: Re: DNS using Name Service Switch module and Casper Message-ID: <CADnZ6Bm96bjJN5gcpCWiNKbNou3XvxZmCD2-YbX34%2B00L=UdPw@mail.gmail.com> In-Reply-To: <X/h%2BJRmXmrOfmXBM@raichu> References: <CADnZ6Bke=9%2B_pMc6rkbheNUWS-H6_X14%2Bf%2BWz5cfUCD=BTwk=g@mail.gmail.com> <X/R7Ahz8sz5v%2BoFa@raichu> <CADnZ6BmUJxVZx155j8opJKNsHJBE5mWz9D=MBE0Y_xu-kgOBfQ@mail.gmail.com> <X/h%2BJRmXmrOfmXBM@raichu>
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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 <markj@freebsd.org>: > > 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 <pid>" 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 <markj@freebsd.org>: > > > > > 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? > > >
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