Testing an upgrade from 1.17.2 to 1.18.0 and all curl requests to
internal names started failing with "Could not resolve host". adig
and ahost are both able to resolve the names just fine. It appears
that this affects any lookup that only returns IPv6 addresses, and
possibly also any lookup that is behind a DNAME. The IPv6 case is
easier to reproduce so that's what I've put below:
This can be easily reproduced from `curl -vs
https://production-all-ipv6.easypost.com/health/ok` on any host with
c-ares 1.18.0 installed and curl linked against c-ares.
Bizarrely enough, if I strace curl, I see it actually connecting to
the correct remote IP before returning the "Could not resolve host"
error. ???
I did a git-bisect run and it points at
778d7cd9e7bf6b31ce697f47cbe935e33a63a5b4
<https://github.com/c-ares/c-ares/commit/778d7cd9e7bf6b31ce697f47cbe935e33a63a5b4> as
the offending commit.
I'm running dnsmasq on localhost and nothing about it has changed.
Below is some probably-relevant output from a system with c-ares
1.17.2 installed system wide and c-ares 1.18.0 installed in the
"./prefix" directory.
$ curl --version
curl 7.79.1 (x86_64-redhat-linux-gnu) libcurl/7.79.1 OpenSSL/1.0.2u
zlib/1.2.3 zstd/1.4.9 c-ares/1.17.2 libidn2/2.3.0 libssh2/1.10.0
nghttp2/1.45.1 OpenLDAP/2.4.40
Release-Date: 2021-09-22
Protocols: dict file ftp ftps gopher gophers http https imap imaps
ldap ldaps mqtt pop3 pop3s rtsp scp sftp smb smbs smtp smtps telnet tftp
Features: alt-svc AsynchDNS HSTS HTTP2 HTTPS-proxy IDN IPv6 Largefile
libz NTLM NTLM_WB SSL UnixSockets zstd
$ env LD_LIBRARY_PATH=./prefix/lib/ curl --version
curl 7.79.1 (x86_64-redhat-linux-gnu) libcurl/7.79.1 OpenSSL/1.0.2u
zlib/1.2.3 zstd/1.4.9 c-ares/1.18.0 libidn2/2.3.0 libssh2/1.10.0
nghttp2/1.45.1 OpenLDAP/2.4.40
Release-Date: 2021-09-22
Protocols: dict file ftp ftps gopher gophers http https imap imaps
ldap ldaps mqtt pop3 pop3s rtsp scp sftp smb smbs smtp smtps telnet tftp
Features: alt-svc AsynchDNS HSTS HTTP2 HTTPS-proxy IDN IPv6 Largefile
libz NTLM NTLM_WB SSL UnixSockets zstd
$ curl https://production-all-ipv6.easypost.com/health/ok
UP
$ env LD_LIBRARY_PATH=./prefix/lib/ curl
https://production-all-ipv6.easypost.com/health/ok
curl: (6) Could not resolve host: production-all-ipv6.easypost.com
<http://production-all-ipv6.easypost.com>
$ env LD_LIBRARY_PATH=./prefix/lib/ strace curl
https://production-all-ipv6.easypost.com/health/ok
[snip]
connect(5, {sa_family=AF_INET6, sin6_port=htons(53),
inet_pton(AF_INET6, "::1", &sin6_addr), sin6_flowinfo=0,
sin6_scope_id=0}, 28) = 0
sendto(5, "Q\337\1\0\0\1\0\0\0\0\0\0\23production-all-ipv6"..., 50,
MSG_NOSIGNAL, NULL, 0) = 50
sendto(5, "~\311\1\0\0\1\0\0\0\0\0\0\23production-all-ipv6"..., 50,
MSG_NOSIGNAL, NULL, 0) = 50
poll([{fd=5, events=POLLIN|POLLRDNORM}], 1, 0) = 1 ([{fd=5,
revents=POLLIN|POLLRDNORM}])
recvfrom(5, "Q\337\201\200\0\1\0\0\0\0\0\0\23production-all-ipv6"...,
4097, 0, {sa_family=AF_INET6, sin6_port=htons(53),
inet_pton(AF_INET6, "::1", &sin6_addr), sin6_flowinfo=0,
sin6_scope_id=0}, [28]) = 50
recvfrom(5, "~\311\201\200\0\1\0\4\0\0\0\0\23production-all-ipv6"...,
4097, 0, {sa_family=AF_INET6, sin6_port=htons(53),
inet_pton(AF_INET6, "::1", &sin6_addr), sin6_flowinfo=0,
sin6_scope_id=0}, [28]) = 162
socket(PF_INET6, SOCK_DGRAM, IPPROTO_UDP) = 6
connect(6, {sa_family=AF_INET6, sin6_port=htons(443),
inet_pton(AF_INET6, "2607:f0d0:2901:7e::3", &sin6_addr),
sin6_flowinfo=0, sin6_scope_id=0}, 28) = 0
getsockname(6, {sa_family=AF_INET6, sin6_port=htons(43428),
inet_pton(AF_INET6, "2607:f0d0:2901:4b::66", &sin6_addr),
sin6_flowinfo=0, sin6_scope_id=0}, [28]) = 0
close(6) = 0
socket(PF_INET6, SOCK_DGRAM, IPPROTO_UDP) = 6
connect(6, {sa_family=AF_INET6, sin6_port=htons(443),
inet_pton(AF_INET6, "2607:f0d0:3803:ca::3", &sin6_addr),
sin6_flowinfo=0, sin6_scope_id=0}, 28) = 0
getsockname(6, {sa_family=AF_INET6, sin6_port=htons(44405),
inet_pton(AF_INET6, "2607:f0d0:2901:4b::66", &sin6_addr),
sin6_flowinfo=0, sin6_scope_id=0}, [28]) = 0
close(6) = 0
socket(PF_INET6, SOCK_DGRAM, IPPROTO_UDP) = 6
connect(6, {sa_family=AF_INET6, sin6_port=htons(443),
inet_pton(AF_INET6, "2607:f0d0:3803:ca::2", &sin6_addr),
sin6_flowinfo=0, sin6_scope_id=0}, 28) = 0
getsockname(6, {sa_family=AF_INET6, sin6_port=htons(33765),
inet_pton(AF_INET6, "2607:f0d0:2901:4b::66", &sin6_addr),
sin6_flowinfo=0, sin6_scope_id=0}, [28]) = 0
close(6) = 0
socket(PF_INET6, SOCK_DGRAM, IPPROTO_UDP) = 6
connect(6, {sa_family=AF_INET6, sin6_port=htons(443),
inet_pton(AF_INET6, "2607:f0d0:2901:7e::2", &sin6_addr),
sin6_flowinfo=0, sin6_scope_id=0}, 28) = 0
getsockname(6, {sa_family=AF_INET6, sin6_port=htons(59083),
inet_pton(AF_INET6, "2607:f0d0:2901:4b::66", &sin6_addr),
sin6_flowinfo=0, sin6_scope_id=0}, [28]) = 0
close(6) = 0
close(5) = 0
rt_sigaction(SIGPIPE, {SIG_IGN, [PIPE], SA_RESTORER|SA_RESTART,
0x7ff5cb5f4570}, NULL, 8) = 0
rt_sigaction(SIGPIPE, {SIG_IGN, [PIPE], SA_RESTORER|SA_RESTART,
0x7ff5cb5f4570}, NULL, 8) = 0
write(2, "c", 1c) = 1
write(2, "u", 1u) = 1
write(2, "r", 1r) = 1
write(2, "l", 1l) = 1
write(2, ":", 1:) = 1
write(2, " ", 1 ) = 1
write(2, "(", 1() = 1
write(2, "6", 16) = 1
write(2, ")", 1)) = 1
write(2, " ", 1 ) = 1
write(2, "C", 1C) = 1
write(2, "o", 1o) = 1
write(2, "u", 1u) = 1
write(2, "l", 1l) = 1
write(2, "d", 1d) = 1
write(2, " ", 1 ) = 1
write(2, "n", 1n) = 1
write(2, "o", 1o) = 1
write(2, "t", 1t) = 1
write(2, " ", 1 ) = 1
write(2, "r", 1r) = 1
write(2, "e", 1e) = 1
write(2, "s", 1s) = 1
write(2, "o", 1o) = 1
write(2, "l", 1l) = 1
write(2, "v", 1v) = 1
write(2, "e", 1e) = 1
write(2, " ", 1 ) = 1
write(2, "h", 1h) = 1
write(2, "o", 1o) = 1
write(2, "s", 1s) = 1
write(2, "t", 1t) = 1
write(2, ":", 1:) = 1
--
James Brown
Engineer
