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
