In case it isn't clear about how this affects security, consider this case: In a small environment without LDAP, NIS, etc, it's not unusual for the users to be created manually, and sometimes out of order, so their uids don't match between servers.
NFS Server: Has users alice (uid 1001), bob (uid 1002), craig (uid 1003) NFS Client 1: Has users alice (uid 1001), bob (uid 1002), craig (uid 1003) NFS Client 2: Has users alice (uid 1001), bob (uid 1003), craig (uid 1002) Let's say each user's home directory is mounted from the server to the clients with nfs. A pretty normal situation. On client machine #1, it would be working as expected. On client machine #2, a sysadmin looking at the mounts would see that they were owned by the expected users. ie. /home/alice is owned by alice, /home/bob is owned by bob, and /home/craig is owned by craig. drwxr-x--- 2 alice users 4096 Mar 28 14:43 alice drwxr-x--- 2 bob users 4096 Mar 30 10:43 bob drwxr-x--- 2 craig users 4096 Mar 29 12:21 craig However because the NFS id mapping is bugged, on client #2 with the non-matched UIDs, it will allow bob to execute something like this: cat /home/craig/top_secret_document echo "pwned" > /home/craig/.bashrc -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/966734 Title: nfs4 allows writes by incorrect users To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/nfs-utils/+bug/966734/+subscriptions -- ubuntu-bugs mailing list [email protected] https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
