netatalk fails to generate unique server signatures

[Craig Ringer]

Binary package hint: netatalk

Description: Ubuntu 9.10
Release: 9.10

ii netatalk 2.0.4~beta2-5ubuntu2 AppleTalk user binaries

NetATalk fails to generate a unique server signature. Analysis of client/server communication reveals that both NetATalk servers here report the signature 01017F0001017F0001017F0001017F00 . This confuses Mac clients, resulting in them apparently randomly directing AFP requests to one server or the other. Users will connect to SERVER1 and get a volume list from SERVER2 or vice versa.

The netatalk code for generating server signatures (etc/afpd/status.c:191) uses the libc gethostid() call to obtain a 32-bit unique identifier for the host.

GNU Libc's man page for gethostid(3) notes that:

"In the glibc implementation, the hostid is stored in the file /etc/hostid. (In glibc versions before 2.2, the file /var/adm/hostid was used.)
"In the glibc implementation, if gethostid() cannot open the file containing the host ID, then it obtains the hostname using gethostname(2), passes that hostname to gethostbyname_r(3) in order to obtain the host's IPv4
       address, and returns a value obtained by bit-twiddling the IPv4 address. (This value may not be unique.)"

Ubuntu systems do not have any /etc/hostid by default, so glibc falls back on gethostbyname_r(3). However, Ubuntu systems' /etc/hosts files map the hostname to 127.0.0.1:

127.0.0.1 localhost
127.0.1.1 HOSTNAME.localnet HOSTNAME

so gethostbyname_r for the hostname in /etc/hostname will always return 127.0.0.1 . gethostid(3) will therefore always return the same value, and NetATalk's system id will always be the same on different Ubuntu hosts.

WORKAROUND:

To each line in your afpd.conf, append an
explicit:

-signature user:SERVERNAME

(if you have more than one line in afpd.conf, make sure the signature is
unique for each one).

[Craig Ringer (ringerc)]

Filed upstream bug: https://sourceforge.net/tracker/index.php?func=detail&aid=2967179&group_id=8642&atid=108642

(Couldn't see how to link it to this bug in Launchpad)

[Craig Ringer (ringerc)]

A workaround for admins: to each line in your afpd.conf, append an
explicit:

-signature user:SERVERNAME

(if you have more than one line in afpd.conf, make sure the signature is
unique for each one).

[C de-Avillez (hggdh2)]

Thank you for opening this bug and helping making Ubuntu better. First of all, thank you for all the work you have done here. Given that upstream has accepted the bug, I am marking it triaged for us. Also:

* I am also adjusting the description to include the workaround you found -- it is a nice way of resolving the conflict;
* I do not know why you added a coreutils task (and this is why this bug got my attention ;-), since there is nothing related to coreutils here. I have marked this task INVALID;
* You could not add an upstream watch because netatalk has not been defined as a project in LP (yet). I will see to it.

[dmarks (markstedt)]

For the record: This bug was fixed with v2.1.0 -- https://sourceforge.net/p/netatalk/bugs/362/