[PATCH 0/3] Misc. redirect_dir=nofollow fixes

Amir Goldstein
2020-07-13T14:19:56Z

Miklos, Vivek,

Following discussion on following an unsafe non-dir origin [1]
and in a addition to a fix for the reported null uuid case [2] and to
Vivek's doc clarification [3], I am proposing to piggy back existing
config redirect_dir=nofollow to also not follow non-dir origin.

Like in the case of non-dir origin, following redirects behavior was
added with no opt-out option in kernel v4.10. Later security concerns
about following malformed redirects resulted in the redirect_dir=nofollow
config option.

Without giving too much thought into how unsafe it can be to follow
a bad origin, there is very low motication IMO to follow non-dir origin
with redirect_dir=nofollow, because it is a configuration that prefers
safety over correctness, so it just seems like the right thing to do.

The first two patches are independent bug fixes related to read-only
NFS export, which can be taken regardless of non-dir origin nofollow.
FYI, I found those bugs because I am using ro,index=off NFS export
configuration for the new overlay fsnotify snaphsot series.

Thanks,
Amir.

[1] https://lore.kernel.org/linux-unionfs/CAJfpegv9h7ubuGy_6K4OCdZd3R7Z4HGmCDB2L7mO5bVoGd6MSA@mail.gmail.com/
[2] https://lore.kernel.org/linux-unionfs/20200708131613.30038-1-amir73il@gmail.com/
[3] https://lore.kernel.org/linux-unionfs/20200709140220.GC150543@redhat.com/

Amir Goldstein (3):
ovl: force read-only sb on failure to create index dir
ovl: fix mount option checks for nfs_export with no upperdir
ovl: do not follow non-dir origin with redirect_dir=nofollow

Documentation/filesystems/overlayfs.rst | 4 +--
fs/overlayfs/namei.c | 2 +-
fs/overlayfs/super.c | 42 ++++++++++++++-----------
3 files changed, 27 insertions(+), 21 deletions(-)

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2.17.1