Public bug reported:

I am running Ubuntu Trusty (3.13.0-65-generic #106-Ubuntu SMP Fri Oct 2
22:08:27 UTC 2015 x86_64 x86_64 x86_64 GNU/Linux).

There are two issues in OverlayFS as follows:

 1. /proc/<pid>/fdinfo/<fd> reports wrong mnt_id (non-existent in
/proc/<pid>/mountinfo)

 2. /proc/<pid>/fd/<fd> shows incorrect path for the symlink target

These issues were previously reported and patched for the Ubuntu Vivid
kernel (3.19) in bug #1479468, but the patch was not applied to the 3.13
kernel, possibly because it contains an older version of overlayfs.

These issues are now adversely affecting some versions of lxc when used
in conjunction with the 3.13 kernel, because lxc has recently been
patched to pass /proc/<pid>/fd/<fd> to the mount syscall.  This change
to lxc was made in response to cve-2015-1335; see bug #1476662.

The kernel issues cause some overlayfs-backed containers to fail to
start, with error message,

strace: mount("/home/ubuntu/test.txt", "/proc/self/fd/16",
0x7ffd4c3f7fdb, MS_BIND, NULL) = -1 EACCES (Permission denied)

The mount fails because /proc/self/fd/16, which should point to a file
in overlayfs, has an invalid value.

The following versions of lxc are affected:

repository                                     lxc version                      
                                       impact 
--------------------------------------------------------------------------------------------------------------------------------------------------
trusty                                          1.0.7-0ubuntu0.7                
                                   not affectd
ppa:ubuntu-lxc/lxc-git-stable-1.0  1.0.7+stable~20151014-2143-0ubuntu1~trusty   
affected
ppa:ubuntu-lxc/lxc-git-stable-1.1  1.1.3+stable~20151007-2301-0ubuntu1~trusty   
affected
ppa:ubuntu-lxc/lxc-git-master      1.1.3+master~20151012-0541-0ubuntu1~trusty  
affected

To reproduce the lxc failure-to-start issue:

# Install the 3.13 kernel and also an affected version of lxc.
lxc-create -t download -n trusty -- -d ubuntu -r trusty -a amd64;
touch $HOME/test.txt;
echo "lxc.mount.entry = $HOME/test.txt home/ubuntu/test.txt none 
bind,create=file 0 0" >> $HOME/.local/share/lxc/trusty/config;
lxc-clone -s -B overlayfs trusty trusty_overlay;
lxc-start -n trusty_overlay; # fails to start

** Affects: linux (Ubuntu)
     Importance: Undecided
         Status: New

** Affects: lxc (Ubuntu)
     Importance: Undecided
         Status: New


** Tags: bot-stop-nagging overlayfs

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https://bugs.launchpad.net/bugs/1507463

Title:
  OverlayFS: Wrong mnt_id and path reported in /proc in linux-3.13

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