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Message-ID: <c874178f-dc16-4725-94e5-5a92f98e424e@SystematicSW.ab.ca>
Date: Wed, 14 Feb 2024 18:08:11 -0700
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Subject: Re: Win 11 Cygwin dns-utils "dig" and "host": Option -6 causes
command to timeout
To: cygwin AT cygwin DOT com
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From: Brian Inglis via Cygwin <cygwin AT cygwin DOT com>
Reply-To: cygwin AT cygwin DOT com
Cc: Brian Inglis <Brian DOT Inglis AT SystematicSW DOT ab DOT ca>
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On 2024-02-14 16:28, Jim Garrison via Cygwin wrote:
> Win 11 Cygwin "dig" and "host": Option -6 causes command to hang
> 
> TL;DR
> -----
> 
> It appears "dig" and "host" both depend on the existence of /etc/resolv.conf, 
> but only when the -6 option (send queries over IPv6) is specified.
> 
> /etc/resolv.conf does not exist on either my old Win 10 or relatively new Win 11 
> systems.
> 
> I have a vague recollection that at some point, maybe Windows 7 or even XP, 
> there was a Cygwin /etc/resolv.conf that was a link to 
> C:\windows\system32\drivers\etc\resolv.conf, but I don't think this has been 
> true for quite a while if it ever was.  Also resolv.conf does not exist in the 
> windows location either.
> 
> Details
> -------
> 
> Sample:
> 
>      # Default query over IPv4
>      $ host google.com
>      google.com has address 74.125.197.102
>      google.com has address 74.125.197.100
>      google.com has address 74.125.197.138
>      google.com has address 74.125.197.101
>      google.com has address 74.125.197.139
>      google.com has address 74.125.197.113
>      google.com has IPv6 address 2607:f8b0:400e:c03::64
>      google.com has IPv6 address 2607:f8b0:400e:c03::71
>      google.com has IPv6 address 2607:f8b0:400e:c03::65
>      google.com has IPv6 address 2607:f8b0:400e:c03::66
>      google.com mail is handled by 10 smtp.google.com.
> 
> 
>      # Query over IPv6
>      $ host -6 google.com
>      ;; connection timed out; no servers could be reached

Ditto!

Without IPv6 nameservers in /etc/resolv.conf I get:

$ host -6 google.com
;; connection timed out; no servers could be reached
Failing assertion due to probable leaked memory in context 0xa00020be0 ("dig") 
(stats[4].gets == 1).
mem.c:1121: INSIST(ctx->stats[i].gets == 0U) failed.

but with IPv6 nameservers in /etc/resolv.conf I get:

$ host -6 google.com
google.com has address 142.251.211.238
google.com has IPv6 address 2607:f8b0:400a:804::200e
google.com mail is handled by 10 smtp.google.com.

>      # Query over IPv6 with explicit DNS server
>      $ host -6 google.com 2601:xxx:xxx:xxx:201:2eff:fe70:3bfe
>      Using domain server:
>      Name: 2601:xxx:xxx:xxx:201:2eff:fe70:3bfe
>      Address: 2601:xxx:xxx:xxx:201:2eff:fe70:3bfe#53
>      Aliases:
> 
>      google.com has address 74.125.197.139
>      google.com has address 74.125.197.113
>      google.com has address 74.125.197.102
>      google.com has address 74.125.197.100
>      google.com has address 74.125.197.138
>      google.com has address 74.125.197.101
>      google.com has IPv6 address 2607:f8b0:400e:c03::71
>      google.com has IPv6 address 2607:f8b0:400e:c03::65
>      google.com has IPv6 address 2607:f8b0:400e:c03::66
>      google.com has IPv6 address 2607:f8b0:400e:c03::64
>      google.com mail is handled by 10 smtp.google.com.
> 
> I ran the failing command above in strace and saw that it's trying to open 
> /etc/resolv.conf
> 
>      [...]
>        206  515079 [main] host 2426 open: open(/etc/resolv.conf, 0x0)
>         58  515137 [main] host 2426 normalize_posix_path: src /etc/resolv.conf
>         59  515196 [main] host 2426 normalize_posix_path: /etc/resolv.conf = 
> normalize_posix_path (/etc/resolv.conf)
>         63  515259 [main] host 2426 mount_info::conv_to_win32_path: 
> conv_to_win32_path (/etc/resolv.conf)
>         68  515327 [main] host 2426 mount_info::cygdrive_win32_path: src 
> '/etc/resolv.conf', dst ''
>         61  515388 [main] host 2426 mount_info::conv_to_win32_path: src_path 
> /etc/resolv.conf, dst C:\cygwin64\etc\resolv.conf, flags 0x30008, rc 0
>         81  515469 [main] host 2426 symlink_info::check: 0xC0000034 = 
> NtCreateFile (\??\C:\cygwin64\etc\resolv.conf)
>         82  515551 [main] host 2426 symlink_info::check: 0xC0000034 = 
> NtQueryInformationFile (\??\C:\cygwin64\etc\resolv.conf)
>         90  515641 [main] host 2426 symlink_info::check: 0xC0000034 = 
> NtCreateFile (\??\C:\cygwin64\etc\resolv.conf.exe)
>         81  515722 [main] host 2426 symlink_info::check: 0xC0000034 = 
> NtQueryInformationFile (\??\C:\cygwin64\etc\resolv.conf.exe)
>         90  515812 [main] host 2426 symlink_info::check: 0xC0000034 = 
> NtCreateFile (\??\C:\cygwin64\etc\resolv.conf.lnk)
>         81  515893 [main] host 2426 symlink_info::check: 0xC0000034 = 
> NtQueryInformationFile (\??\C:\cygwin64\etc\resolv.conf.lnk)
>         88  515981 [main] host 2426 symlink_info::check: 0xC0000034 = 
> NtCreateFile (\??\C:\cygwin64\etc\resolv.conf.exe.lnk)
>         82  516063 [main] host 2426 symlink_info::check: 0xC0000034 = 
> NtQueryInformationFile (\??\C:\cygwin64\etc\resolv.conf.exe.lnk)
>         81  516144 [main] host 2426 symlink_info::check: 0 = 
> symlink.check(C:\cygwin64\etc\resolv.conf, 0x7FFFFB4B0) (mount_flags 0x30008, 
> path_flags 0x0)
>         64  516208 [main] host 2426 mount_info::conv_to_win32_path: 
> conv_to_win32_path (/etc)
>         59  516267 [main] host 2426 mount_info::cygdrive_win32_path: src '/etc', 
> dst ''
>         60  516327 [main] host 2426 mount_info::conv_to_win32_path: src_path 
> /etc, dst C:\cygwin64\etc, flags 0x30008, rc 0
>         69  516396 [main] host 2426 symlink_info::check: 0x0 = NtCreateFile 
> (\??\C:\cygwin64\etc)
>        233  516629 [main] host 2426 symlink_info::check: not a symlink
>         65  516694 [main] host 2426 symlink_info::check: 0 = 
> symlink.check(C:\cygwin64\etc, 0x7FFFFB4B0) (mount_flags 0x30008, path_flags 0x0)
>         62  516756 [main] host 2426 path_conv::check: 
> this->path(C:\cygwin64\etc\resolv.conf), has_acls(1)
>         61  516817 [main] host 2426 build_fh_pc: fh 0x80000BE18, dev 000000C3
>         60  516877 [main] host 2426 fhandler_base::open: 
> (\??\C:\cygwin64\etc\resolv.conf, 0x0)
>         89  516966 [main] host 2426 seterrno_from_nt_status: 
> /cygdrive/d/a/scallywag/cygwin/cygwin-3.5.0-1.x86_64/src/newlib-cygwin/winsup/cygwin/fhandler/base.cc:717 status 0xC0000034 -> windows error 2
>         75  517041 [main] host 2426 geterrno_from_win_error: windows error 2 == 
> errno 2
>         59  517100 [main] host 2426 fhandler_base::open: 0xC0000034 = 
> NtCreateFile (0x7FF84CA3A060, 0x80100000, \??\C:\cygwin64\etc\resolv.conf, io, 
> NULL, 0x0, 0x7, 0x1, 0x4020, NULL, 0)
>         85  517185 [main] host 2426 fhandler_base::open: 0 = 
> fhandler_base::open(\??\C:\cygwin64\etc\resolv.conf, 0x0)
>         90  517275 [main] host 2426 fhandler_base::open_fs: 0 = 
> fhandler_disk_file::open(\??\C:\cygwin64\etc\resolv.conf, 0x0)
>         90  517365 [main] host 2426 open: -1 = open(/etc/resolv.conf, 0x0), errno 2
>      [...]
> 
> I confirmed this was the problem by creating /etc/resolv.conf (within the Cygwin 
> root, not a symlink) and included the search domain and IPv4 and IPv6 dns 
> servers, after which the -6 option no longer timed out.

I added a Cygwin postinstall script:

	/etc/postinstall/0p_l_etc_resolv_conf.dash

to create resolv.conf from `ipconfig /all` DNS servers, an internal list of open 
public DNS servers, and search domains, update:

	/var/run/resolvconf/resolv.conf

when changed, and `ln -frsvt /etc/`, also run from a Scheduled Task on System 
Restart.

-- 
Take care. Thanks, Brian Inglis              Calgary, Alberta, Canada

La perfection est atteinte                   Perfection is achieved
non pas lorsqu'il n'y a plus rien à ajouter  not when there is no more to add
mais lorsqu'il n'y a plus rien à retirer     but when there is no more to cut
                                 -- Antoine de Saint-Exupéry

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