[Bug 1950] New: sshd tries to bind over and over to ::1 for several seconds

[bugzilla-daemon at bugzilla.mindrot.org]

https://bugzilla.mindrot.org/show_bug.cgi?id=1950

             Bug #: 1950
           Summary: sshd tries to bind over and over to ::1 for several
                    seconds
    Classification: Unclassified
           Product: Portable OpenSSH
           Version: 5.9p1
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: normal
          Priority: P2
         Component: sshd
        AssignedTo: unassigned-bugs at mindrot.org
        ReportedBy: arekm at pld-linux.org


Created attachment 2105
  --> https://bugzilla.mindrot.org/attachment.cgi?id=2105
sshd log for that

When AF_INET6 socket creation is allowed but bind()ing to ::1 is
impossible then sshd loops until MAX_DISPLAYS is reached trying to bind
to ::1 and then fails. This takes several seconds unfortunately which
slows down login process a lot.

When such scenario can happen, so AF_INET6 socket creation is allowed
but ::1 doesn't exist? This can happen in linux-vserver.org guest or on
a pure Linux system with net.ipv6.conf.all.disable_ipv6 sysctl set to
1.


That how it looks under strace:

28636 10:33:49 socket(PF_INET6, SOCK_DGRAM, IPPROTO_IP) = 6 <0.000020>
28636 10:33:49 connect(6, {sa_family=AF_INET6, sin6_port=htons(6493),
inet_pton(AF_INET6, "::1", &sin6_addr), sin6_flowinfo=0,
sin6_scope_id=0}, 28) = -1 EAD
DRNOTAVAIL (Cannot assign requested address) <0.000020>
28636 10:33:49 connect(6, {sa_family=AF_UNSPEC,
sa_data="\0\0\0\0\0\0\0\0\0\0\0\0\0\0"}, 16) = 0 <0.000019>
28636 10:33:49 connect(6, {sa_family=AF_INET, sin_port=htons(6493),
sin_addr=inet_addr("127.0.0.1")}, 16) = 0 <0.000020>
28636 10:33:49 getsockname(6, {sa_family=AF_INET6,
sin6_port=htons(37600), inet_pton(AF_INET6, "::ffff:127.0.100.1",
&sin6_addr), sin6_flowinfo=0, sin6_scope
_id=0}, [28]) = 0 <0.000015>
28636 10:33:49 close(6)                 = 0 <0.000013>
28636 10:33:49 socket(PF_INET, SOCK_STREAM, IPPROTO_TCP) = 6 <0.000020>
28636 10:33:49 setsockopt(6, SOL_SOCKET, SO_REUSEADDR, [1], 4) = 0
<0.000015>
28636 10:33:49 bind(6, {sa_family=AF_INET, sin_port=htons(6493),
sin_addr=inet_addr("127.0.0.1")}, 16) = 0 <0.000012>
28636 10:33:49 socket(PF_INET6, SOCK_STREAM, IPPROTO_TCP) = 7
<0.000017>
28636 10:33:49 socket(PF_FILE, SOCK_DGRAM|SOCK_CLOEXEC, 0) = 8
<0.000012>
28636 10:33:49 connect(8, {sa_family=AF_FILE, path="/dev/log"}, 110) =
-1 EPROTOTYPE (Protocol wrong type for socket) <0.000016>
28636 10:33:49 close(8)                 = 0 <0.000016>
28636 10:33:49 socket(PF_FILE, SOCK_STREAM|SOCK_CLOEXEC, 0) = 8
<0.000012>
28636 10:33:49 connect(8, {sa_family=AF_FILE, path="/dev/log"}, 110) =
0 <0.000033>
28636 10:33:49 sendto(8, "<39>Nov 12 10:33:49 sshd[28636]: debug3:
sock_set_v6only: set socket 7 IPV6_V6ONLY\0", 83, MSG_NOSIGNAL, NULL,
0) = 83 <0.000047>
28636 10:33:49 close(8)                 = 0 <0.000024>
28636 10:33:49 setsockopt(7, SOL_IPV6, IPV6_V6ONLY, [1], 4) = 0
<0.000011>
28636 10:33:49 setsockopt(7, SOL_SOCKET, SO_REUSEADDR, [1], 4) = 0
<0.000021>
28636 10:33:49 bind(7, {sa_family=AF_INET6, sin6_port=htons(6493),
inet_pton(AF_INET6, "::1", &sin6_addr), sin6_flowinfo=0,
sin6_scope_id=0}, 28) = -1 EADDRN
OTAVAIL (Cannot assign requested address) <0.000020>
28636 10:33:49 socket(PF_FILE, SOCK_DGRAM|SOCK_CLOEXEC, 0) = 8
<0.000020>
28636 10:33:49 connect(8, {sa_family=AF_FILE, path="/dev/log"}, 110) =
-1 EPROTOTYPE (Protocol wrong type for socket) <0.000016>
28636 10:33:49 close(8)                 = 0 <0.000020>
28636 10:33:49 socket(PF_FILE, SOCK_STREAM|SOCK_CLOEXEC, 0) = 8
<0.000020>
28636 10:33:49 connect(8, {sa_family=AF_FILE, path="/dev/log"}, 110) =
0 <0.000040>
28636 10:33:49 sendto(8, "<39>Nov 12 10:33:49 sshd[28636]: debug2: bind
port 6493: Cannot assign requested address\0", 89, MSG_NOSIGNAL, NULL,
0) = 89 <0.000
055>
28636 10:33:49 close(8)                 = 0 <0.000031>
28636 10:33:49 close(7)                 = 0 <0.000021>
28636 10:33:49 close(6)                 = 0 <0.000020>

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