Insecure hostname in nsm_make_temp_pathname

["Philip Rowlands" <linux-nfs@dimebar.com>]

If a host dies after nsm_make_temp_pathname but before rename(temp, path) we may be left with paths resembling .../server.example.com.new

Some clever person has registered and installed a wildcard DNS record for *.com.new.

$ host server.example.com.new
server.example.com.new has address 104.21.68.132
server.example.com.new has address 172.67.195.202

You can see where this is going...

Our firewall scanners tripped on outbound access to this address, port 111, I assume due to NSM reboot notifications.

Suggested workarounds include:
* explicitly skip over paths matching the expect tempname pattern in nsm_load_dir()
* use a different tmp suffix than .new, e.g. one which won't work in DNS

Steps to reproduce:

# cat /var/lib/nfs/statd/sm/server.example.com.new
0100007f 000186b5 00000003 00000010 89ae3382e989d91800000000dc00ed000000ffff 1.2.3.4 my-client-name
# sm-notify -d -f -n
sm-notify: Version 2.7.1 starting
sm-notify: Retired record for mon_name server.example.com.new
sm-notify: Added host server.example.com.new to notify list
sm-notify: Initializing NSM state
sm-notify: Failed to open /proc/sys/fs/nfs/nsm_local_state: No such file or directory
sm-notify: Effective UID, GID: 29, 29
sm-notify: Sending PMAP_GETPORT for 100024, 1, udp
sm-notify: Added host server.example.com.new to notify list
sm-notify: Host server.example.com.new due in 2 seconds
sm-notify: Sending PMAP_GETPORT for 100024, 1, udp
# etc.

tcpdump shows the outbound traffic:
22:42:31.940208 IP 192.168.0.131.819 > 172.67.195.202.sunrpc: UDP, length 56
22:42:33.942440 IP 192.168.0.131.819 > 172.67.195.202.sunrpc: UDP, length 56
22:42:37.946903 IP 192.168.0.131.819 > 172.67.195.202.sunrpc: UDP, length 56

The client statd was artificially placed for the purposes of showing the problem, but I hope it's close enough to make sense.


Cheers,
Phil