[Samba] Bug 6870 resurfaced in Samba 4.2.10

[Rebecca Gellman]

According to this bugzilla entry, bug 6870 has been fixed as of at least
version 3.5: 

https://bugzilla.samba.org/show_bug.cgi?id=6870 

However, I assert that it is present in 4.2.10, which ships with Debian
Jessie. 

On my home network (IPv4 and IPv6), a box with Samba 4.2.10 with IPv6
disabled (via sysctl), will fail to contact a DC because the IPv6
connect fails immediately before the v4 connect has a chance to succeed.


I determined this by strace'ing the "net ads workgroup" command, which
resulted in the following: 

11:41:52 socket(PF_INET, SOCK_DGRAM, IPPROTO_IP) = 11 <0.000027>
11:41:52 fcntl(11, F_GETFL) = 0x2 (flags O_RDWR) <0.000015>
11:41:52 fcntl(11, F_SETFL, O_RDWR|O_NONBLOCK) = 0 <0.000016>
11:41:52 fcntl(11, F_GETFD) = 0 <0.000015>
11:41:52 fcntl(11, F_SETFD, FD_CLOEXEC) = 0 <0.000016>
11:41:52 connect(11, {sa_family=AF_INET, sin_port=htons(389),
sin_addr=inet_addr("192.168.81.132")}, 16) = 0 <0.000050>
11:41:52 socket(PF_INET6, SOCK_DGRAM, IPPROTO_IP) = 12 <0.000025>
11:41:52 fcntl(12, F_GETFL) = 0x2 (flags O_RDWR) <0.000016>
11:41:52 fcntl(12, F_SETFL, O_RDWR|O_NONBLOCK) = 0 <0.000015>
11:41:52 fcntl(12, F_GETFD) = 0 <0.000016>
11:41:52 fcntl(12, F_SETFD, FD_CLOEXEC) = 0 <0.000015>
11:41:52 setsockopt(12, SOL_IPV6, IPV6_V6ONLY, [1], 4) = 0 <0.000018>
11:41:52 connect(12, {sa_family=AF_INET6, sin6_port=htons(389),
inet_pton(AF_INET6, "2001:8b0:1627:1::2", &sin6_addr), sin6_flowinfo=0,
sin6_scope_id=0}, 28) = -1 ENETUNREACH (Network is unreachable)
<0.000032>
11:41:52 close(12) = 0 <0.000028>
11:41:52 close(11) = 0 <0.000024>
11:41:52 close(10) = 0 <0.000020>
11:41:52 fcntl(8, F_SETLKW, {type=F_RDLCK, whence=SEEK_SET, start=288,
len=1}) = 0 <0.000021>
11:41:52 fcntl(8, F_SETLKW, {type=F_UNLCK, whence=SEEK_SET, start=288,
len=1}) = 0 <0.000018>
11:41:52 fcntl(9, F_SETLKW, {type=F_WRLCK, whence=SEEK_SET, start=48,
len=1}) = 0 <0.000019>
11:41:52 fcntl(9, F_SETLKW, {type=F_UNLCK, whence=SEEK_SET, start=48,
len=1}) = 0 <0.000032>
11:41:52 fcntl(9, F_SETLKW, {type=F_WRLCK, whence=SEEK_SET, start=48,
len=1}) = 0 <0.000019>
11:41:52 fcntl(9, F_SETLKW, {type=F_UNLCK, whence=SEEK_SET, start=48,
len=1}) = 0 <0.000017>
11:41:52 write(2, "ads_connect: No logon servers\n", 30ads_connect: No
logon servers 

As you can see, sockets 11 and 12 are setup to contact the DC, 11 to v4,
and 12 to v6. connect() on socket 11 is successful (returns 0), but
connect() on socket 12 returns -1 due to "Network unreachable" - this is
correct as the box in question does not have IPv6. 

The attempt is abandoned (implied by the immediate closing of sockets 11
and 12, and the writing of "No logon servers" to stderr) before any
attempt is made to talk on socket 11 (v4). 

After futzing the box to have an IPv6 address with appropriate routing,
the attempt succeeds as expected. However, for reasons (too long to go
into here) this is not a solution, only a means of proving the problem. 

Since most DCs publish v6 records of some kind in DNS in an AD setup
these days, it would seem that this behaviour could do with urgently
fixing. 

Any comments from the samba bods, or should I forward this on to
samba-technical ? 

Thanks 

-- Rebecca Gellman