linux-kernel - [PATCH bpf-next 0/4] bpf path iterator

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Message-ID: <20250528222623.1373000-1-song@kernel.org>
Date: Wed, 28 May 2025 15:26:19 -0700
From: Song Liu <song@...nel.org>
To: bpf@...r.kernel.org,
	linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	linux-security-module@...r.kernel.org
Cc: kernel-team@...a.com,
	andrii@...nel.org,
	eddyz87@...il.com,
	ast@...nel.org,
	daniel@...earbox.net,
	martin.lau@...ux.dev,
	viro@...iv.linux.org.uk,
	brauner@...nel.org,
	jack@...e.cz,
	kpsingh@...nel.org,
	mattbobrowski@...gle.com,
	amir73il@...il.com,
	repnop@...gle.com,
	jlayton@...nel.org,
	josef@...icpanda.com,
	mic@...ikod.net,
	gnoack@...gle.com,
	Song Liu <song@...nel.org>
Subject: [PATCH bpf-next 0/4] bpf path iterator

In security use cases, it is common to apply rules to VFS subtrees.
However, filtering files in a subtree is not straightforward [1].

One solution to this problem is to start from a path and walk up the VFS
tree (towards the root). Among in-tree LSMs, Landlock uses this solution.

BPF LSM solutions, such like Tetragon [2], also use similar approaches.
However, due to lack of proper helper/kfunc support, BPF LSM solutions
usually do the path walk with probe read, which is racy.

This patchset introduce a reliable helper path_parent, which walks path to
its VFS parent. The helper is use in Landlock.

A new BPF iterator, path iterator, is introduced to do the path walking.
The BPF path iterator uses the new path_parent help to walk the VFS tree
reliably.

[1] https://lpc.events/event/18/contributions/1940/
[2] https://github.com/cilium/tetragon/

Song Liu (4):
  namei: Introduce new helper function path_parent()
  landlock: Use path_parent()
  bpf: Introduce path iterator
  selftests/bpf: Add tests for bpf path iterator

 fs/namei.c                                    |  39 +++++
 include/linux/namei.h                         |   8 ++
 kernel/bpf/Makefile                           |   1 +
 kernel/bpf/helpers.c                          |   3 +
 kernel/bpf/path_iter.c                        |  74 ++++++++++
 kernel/bpf/verifier.c                         |   5 +
 security/landlock/fs.c                        |  34 ++---
 .../testing/selftests/bpf/bpf_experimental.h  |   6 +
 .../selftests/bpf/prog_tests/path_iter.c      |  12 ++
 tools/testing/selftests/bpf/progs/path_iter.c | 134 ++++++++++++++++++
 10 files changed, 299 insertions(+), 17 deletions(-)
 create mode 100644 kernel/bpf/path_iter.c
 create mode 100644 tools/testing/selftests/bpf/prog_tests/path_iter.c
 create mode 100644 tools/testing/selftests/bpf/progs/path_iter.c

--
2.47.1