[PATCH v3 bpf-next 0/4] Introduce bpf_cgroup_read_xattr

[Song Liu <song@kernel.org>]

Introduce a new kfunc bpf_cgroup_read_xattr, which can read xattr from
cgroupfs nodes. The primary users are LSMs, cgroup programs, and sched_ext.

---

Changes v2 => v3:
1. Make bpf_cgroup_read_xattr available to all program types.
2. Fix gcc build warning on the selftests.
3. Add "ifdef CONFIG_CGROUPS" around bpf_cgroup_read_xattr.

v2: https://lore.kernel.org/bpf/20250619220114.3956120-1-song@kernel.org/

Changes v1 => v2:
1. Replace 1/4 in v1 with Chritian's version (1/5 in v2).
2. Rename bpf_kernfs_read_xattr => bpf_cgroup_read_xattr, and limit access
   to cgroup only.
3. Add 5/5, which makes bpf_cgroup_read_xattr available to cgroup and
   struct_ops programs.

v1: https://lore.kernel.org/bpf/20250618233739.189106-1-song@kernel.org/

Christian Brauner (1):
  kernfs: remove iattr_mutex

Song Liu (3):
  bpf: Introduce bpf_cgroup_read_xattr to read xattr of cgroup's node
  bpf: Mark cgroup_subsys_state->cgroup RCU safe
  selftests/bpf: Add tests for bpf_cgroup_read_xattr

 fs/bpf_fs_kfuncs.c                            |  34 ++++
 fs/kernfs/inode.c                             |  74 ++++----
 kernel/bpf/helpers.c                          |   3 +
 kernel/bpf/verifier.c                         |   5 +
 .../testing/selftests/bpf/bpf_experimental.h  |   3 +
 .../selftests/bpf/prog_tests/cgroup_xattr.c   | 145 ++++++++++++++++
 .../selftests/bpf/progs/cgroup_read_xattr.c   | 158 ++++++++++++++++++
 .../selftests/bpf/progs/read_cgroupfs_xattr.c |  60 +++++++
 8 files changed, 448 insertions(+), 34 deletions(-)
 create mode 100644 tools/testing/selftests/bpf/prog_tests/cgroup_xattr.c
 create mode 100644 tools/testing/selftests/bpf/progs/cgroup_read_xattr.c
 create mode 100644 tools/testing/selftests/bpf/progs/read_cgroupfs_xattr.c

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2.47.1