[lxc-devel] [lxc/lxc] db4219: autodev: adapt to changes in Linux 4.18

[GitHub]

  Branch: refs/heads/stable-2.0
  Home:   https://github.com/lxc/lxc
  Commit: db4219603946649474b5cb7915dbd6c17ec728f0
      https://github.com/lxc/lxc/commit/db4219603946649474b5cb7915dbd6c17ec728f0
  Author: Christian Brauner <christian.brauner at ubuntu.com>
  Date:   2018-10-14 (Sun, 14 Oct 2018)

  Changed paths:
    M src/lxc/conf.c

  Log Message:
  -----------
  autodev: adapt to changes in Linux 4.18

Starting with commit
55956b59df33 ("vfs: Allow userns root to call mknod on owned filesystems.")
Linux will allow mknod() in user namespaces for userns root if CAP_MKNOD is
available.
However, these device nodes are useless since

static struct super_block *alloc_super(struct file_system_type *type, int flags,
                                 struct user_namespace *user_ns)
{
    /* <snip> */

    if (s->s_user_ns != &init_user_ns)
      s->s_iflags |= SB_I_NODEV;

    /* <snip> */
}

will set the SB_I_NODEV flag on the filesystem. When a device node created in
non-init userns is open()ed the call chain will hit:

bool may_open_dev(const struct path *path)
{
    return !(path->mnt->mnt_flags & MNT_NODEV) &&
      !(path->mnt->mnt_sb->s_iflags & SB_I_NODEV);
}

which will cause an EPERM because the device node is located on an fs
owned by non-init-userns and thus doesn't grant access to device nodes due to
SB_I_NODEV.

This commit enables LXC to deal with such kernels.

Signed-off-by: Christian Brauner <christian.brauner at ubuntu.com>



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