Bug 1418962

Description of problem:

On RHEL 7:

# ip netns add fred
# tail -1 /proc/self/mounts
proc net:[4026532208] proc rw,nosuid,nodev,noexec,relatime 0 0
# ip netns del fred

But on upstream kernels:

# ip netns add fred
# tail -1 /proc/self/mounts
nsfs /run/netns/fred nsfs rw 0 0
# ip netns del fred

Notice that on RHEL 7, the second field (mnt_dir) shows a non-path
net:[INODE], but on upstream kernels this is resolved to a path.

This difference matters for open-vm-tools & container support,
see bug 1166465.

I believe the fix for this is the following, which is not currently
included in the RHEL 7 kernel:

commit f48cfddc6729ef133933062320039808bafa6f45
Author: Eric W. Biederman <ebiederm>
Date:   Fri Nov 8 16:31:29 2013 -0800

    vfs: In d_path don't call d_dname on a mount point
    
    Aditya Kali (adityakali) wrote:
    > Commit bf056bfa80596a5d14b26b17276a56a0dcb080e5:
    > "proc: Fix the namespace inode permission checks." converted
    > the namespace files into symlinks. The same commit changed
    > the way namespace bind mounts appear in /proc/mounts:
    >   $ mount --bind /proc/self/ns/ipc /mnt/ipc
    > Originally:
    >   $ cat /proc/mounts | grep ipc
    >   proc /mnt/ipc proc rw,nosuid,nodev,noexec 0 0
    >
    > After commit bf056bfa80596a5d14b26b17276a56a0dcb080e5:
    >   $ cat /proc/mounts | grep ipc
    >   proc ipc:[4026531839] proc rw,nosuid,nodev,noexec 0 0
    >
    > This breaks userspace which expects the 2nd field in
    > /proc/mounts to be a valid path.
    
    The symlink /proc/<pid>/ns/{ipc,mnt,net,pid,user,uts} point to
    dentries allocated with d_alloc_pseudo that we can mount, and
    that have interesting names printed out with d_dname.
    
    When these files are bind mounted /proc/mounts is not currently
    displaying the mount point correctly because d_dname is called instead
    of just displaying the path where the file is mounted.
    
    Solve this by adding an explicit check to distinguish mounted pseudo
    inodes and unmounted pseudo inodes.  Unmounted pseudo inodes always
    use mount of their filesstem as the mnt_root  in their path making
    these two cases easy to distinguish.
    
    CC: stable.org
    Acked-by: Serge Hallyn <serge.hallyn>
    Reported-by: Aditya Kali <adityakali>
    Signed-off-by: "Eric W. Biederman" <ebiederm>

Version-Release number of selected component (if applicable):

kernel-3.10.0-514.el7.x86_64

How reproducible:

100%

Steps to Reproduce:
1. See steps in the description above.