"Could not resolve host" for IPv6-only names with curl in 1.18.0
James Brown
jbrown at easypost.com
Tue Oct 26 23:16:12 CEST 2021
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
$ 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
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