kernel-packages team mailing list archive

[Serge Hallyn <1531747@xxxxxxxxxxxxxxxxxx>]

in ovl_clear_empty(), the opaque bit is set on the dir in workingdir

in ovl_create_over_whiteout() (the case we're currently looking at) it is
also being set in the working dir.

in ovl_rename2(), it is set in two places, on the upper dentries for
both the old and new.

So it is never set on the lowerdir, at least.

I'm still looking, but it may be safe to say that all needed inode
checks are already done before we call ovl_set_opaque() so that we
can indeed just use prepare_kernel_cred(NULL) instead of prepare_cred().

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https://bugs.launchpad.net/bugs/1531747

Title:
  overlay: mkdir fails if directory exists in lowerdir in a user
  namespace

Status in linux package in Ubuntu:
  Triaged
Status in linux source package in Wily:
  Triaged
Status in linux source package in Xenial:
  Triaged

Bug description:
  If a directory exists in the lowerdir but not in the mounted
  overlay, then mkdir of the directory in the target dir results
  in a mysterious -EPERM.  I've seen this both in wily kernel
  (4.2.0-22-generic #27-Ubuntu) and in a hand-built xenial
  master-next (with unrelated patches added).

  =====================================================
  #!/bin/sh -ex
  dir=`mktemp -d`
  cleanup() {
   umount -l $dir/t
   rm -rf $dir
  }

  trap cleanup EXIT

  echo "dir is $dir"
  mkdir -p $dir/l $dir/u $dir/w $dir/t
  mkdir $dir/l/dev
  mount -t overlay -o lowerdir=$dir/l,upperdir=$dir/u,workdir=$dir/w o $dir/t
  stat $dir/t/dev
  rmdir $dir/t/dev
  mkdir $dir/t/dev
  echo $?
  echo "mkdir should have succeeded"
  =====================================================

  The above will work on the host, but fail in a user namespace, i.e
  in a regular lxd container.

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