[PATCH 0/7] proc: block mounts below /proc/<pid>/net and on the links into /proc/self

[Aleksa Sarai]

On 2026-10-24, Christian Brauner <brauner at kernel.org> wrote:
> Nuke this crap.
> 
> [1]: https://lore.kernel.org/r/20240806-work-procfs-v1-0-fb04e1d09f0c@kernel.org
> 
> Signed-off-by: Christian Brauner (Amutable) <brauner at kernel.org>
> ---
> Christian Brauner (7):
>       proc: don't let an entry below /proc/<pid>/net be a mountpoint
>       proc: don't let /proc/self and /proc/thread-self be mountpoints
>       proc: don't let /proc/mounts and /proc/net be mountpoints
>       afs: create /proc/fs/afs with proc_self_symlink()
>       nfs: create the /proc/fs/nfsfs links with proc_self_symlink()
>       proc: explain which entries can't be mountpoints
>       selftests/proc: test which entries can't be mountpoints

I love it, nuke it from orbit.

Reviewed-by: Aleksa Sarai <aleksa at amutable.com>

The proc_net_d_revalidate() thing is particularly wild, I'm surprised it
hadn't come up to us in bug reports in the past ~10 years. I guess
nobody cared enough to try to mask it?

And yeah, it's a shame we couldn't kill this entirely but I'm looking
forward to the patch you mentioned that restricts who and what can be
over-mounted.

>  fs/afs/main.c                                   |   2 +-
>  fs/nfs/client.c                                 |   4 +-
>  fs/proc/generic.c                               |  31 ++++-
>  fs/proc/internal.h                              |  18 ++-
>  fs/proc/proc_net.c                              |   2 +-
>  fs/proc/root.c                                  |   2 +-
>  fs/proc/self.c                                  |   2 +
>  fs/proc/thread_self.c                           |   2 +
>  include/linux/proc_fs.h                         |   5 +
>  tools/testing/selftests/proc/.gitignore         |   1 +
>  tools/testing/selftests/proc/Makefile           |   1 +
>  tools/testing/selftests/proc/proc-unmountable.c | 150 ++++++++++++++++++++++++
>  12 files changed, 208 insertions(+), 12 deletions(-)
> ---
> base-commit: 7be4bc52fd9e0e55dc9a2e0232b89427d2c4b614
> change-id: 20261024-work-procfs-fixes-8b21a6d17448

-- 
Aleksa Sarai
Founding Engineer at Amutable
https://www.cyphar.com/
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