[Bug 1058851] [NEW] Access denied when mounting IPv4 NFS share on dual-stacked client

[Russell Phillips]

Public bug reported:

Here is my (censored) /etc/exports on my server (Running Ubuntu 12.04),
which is currently dual-stacked:

-------------------
# Public Storage (write)
#ipv6
/export                                2001:xxxx:xxxx:xxxx::/64(rw,async,no_subtree_check)
/export/home                   2001:xxxx:xxxx:xxxx::/64(rw,async,no_subtree_check,nohide,no_root_squash)
/export/home/pub/unmirrored    2001:xxxx:xxxx:xxxx::/64(rw,async,no_subtree_check,nohide,no_root_squash)

# ipv4
/export                         192.168.1.0/24(rw,async,no_subtree_check)
/export/home                    192.168.1.0/24(rw,async,no_subtree_check,nohide,no_root_squash)
/export/home/pub/unmirrored     192.168.1.0/24(rw,async,no_subtree_check,nohide,no_root_squash)
-------------------

This is the mount command I issue from the client:
-------------------
sudo mount bender:/export/home/pub /mnt/pub -t nfs
-------------------

This config works as expected. However, I get the following error if I
remove the IPv6 config lines from /etc/exports, and attempt to mount a
share on a dual-stacked client running Quantal:

-------------------
mount.nfs: access denied by server while mounting bender:/export/home/pub
-------------------

If I then disable IPv6 at the client, it will then mount as expected.

Most importantly: This does not break in Ubuntu 12.04. A dual-stacked
12.04 client will successfully mount an NFS share which is only exported
over IPv4.

In short, to replicate the error:
- Both client and server are dual-stacked
- Client is running Quantal
- /etc/exports on server is exporting NFS shares ONLY over an IPv4 subnet.

** Affects: nfs-utils (Ubuntu)
     Importance: Undecided
         Status: New

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https://bugs.launchpad.net/bugs/1058851

Title:
  Access denied when mounting IPv4 NFS share on dual-stacked client

Status in “nfs-utils” package in Ubuntu:
  New

Bug description:
  Here is my (censored) /etc/exports on my server (Running Ubuntu
  12.04), which is currently dual-stacked:

  -------------------
  # Public Storage (write)
  #ipv6
  /export                                2001:xxxx:xxxx:xxxx::/64(rw,async,no_subtree_check)
  /export/home                   2001:xxxx:xxxx:xxxx::/64(rw,async,no_subtree_check,nohide,no_root_squash)
  /export/home/pub/unmirrored    2001:xxxx:xxxx:xxxx::/64(rw,async,no_subtree_check,nohide,no_root_squash)

  # ipv4
  /export                         192.168.1.0/24(rw,async,no_subtree_check)
  /export/home                    192.168.1.0/24(rw,async,no_subtree_check,nohide,no_root_squash)
  /export/home/pub/unmirrored     192.168.1.0/24(rw,async,no_subtree_check,nohide,no_root_squash)
  -------------------

  This is the mount command I issue from the client:
  -------------------
  sudo mount bender:/export/home/pub /mnt/pub -t nfs
  -------------------

  This config works as expected. However, I get the following error if I
  remove the IPv6 config lines from /etc/exports, and attempt to mount a
  share on a dual-stacked client running Quantal:

  -------------------
  mount.nfs: access denied by server while mounting bender:/export/home/pub
  -------------------

  If I then disable IPv6 at the client, it will then mount as expected.

  Most importantly: This does not break in Ubuntu 12.04. A dual-stacked
  12.04 client will successfully mount an NFS share which is only
  exported over IPv4.

  In short, to replicate the error:
  - Both client and server are dual-stacked
  - Client is running Quantal
  - /etc/exports on server is exporting NFS shares ONLY over an IPv4 subnet.

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