[PATCH bpf v5 0/3] bpf: Fix incorrect handling of user flags by percpu map updates

[Masoud Aghasi <maghasi@disroot.org>]

For BPF_MAP_TYPE_PERCPU_ARRAY map, bpf_percpu_array_update()
is not considering the possibility of a combination of
(BPF_NOEXIST, BPF_EXIST) flags with (BPF_F_CPU, BPF_F_ALL_CPUS) flags.
This causes the (BPF_NOEXIST, BPF_EXIST) flags to lose their effect
in some cases.

For BPF_MAP_TYPE_PERCPU_HASH and BPF_MAP_TYPE_LRU_PERCPU_HASH maps,
htab_map_check_update_flags() and check_flags() are not considering
the possibility of a combination of (BPF_NOEXIST, BPF_EXIST) flags
with (BPF_F_CPU, BPF_F_ALL_CPUS) flags. This causes the
(BPF_NOEXIST, BPF_EXIST) flags to lose their effect in some cases.

For example, when using (BPF_F_CPU | BPF_EXIST) flag combination
with bpf_map_update_elem() on a BPF_MAP_TYPE_PERCPU_HASH map, the
BPF_EXIST flag does not prevent new insertions as expected.

This series fixes the bug by adding proper flag validations and checks
and adds regression tests.

V5 changes:
- Simplify flag validations by introducing new macros in bpf.h
- Add helpers to verify the values after updates in the new tests
- Improve the style and structure of the new tests

V4 changes: https://lore.kernel.org/bpf/20261004111007.3216186-1-maghasi@disroot.org/T/
- Edit selftest to use proper value_sz in the new cgroup map test
- Edit selftest to pin the current pid to the current cpu for LRU map
- Edit commit messages to include user-visible changes

V3 changes: https://lore.kernel.org/bpf/20261003160213.2641506-1-maghasi@disroot.org/T/
- Split the fix into two separate patches for array map and hash maps
- Extend the selftest to cover all percpu map types
- Extend the selftest to cover all applicable flag combinations
- Extend the selftest to cover the unnecessary delete issue of LRU map

V2 changes: https://lore.kernel.org/bpf/20260930135753.1063495-1-maghasi@disroot.org/T/
- Fix a BPF_EXIST flag check in __htab_lru_percpu_map_update_elem()
- Add additional test for BPF_MAP_TYPE_LRU_PERCPU_HASH map
- Add check for BPF_EXIST, BPF_NOEXIST combination in percpu array map

V1: https://lore.kernel.org/bpf/20260928102821.995214-1-maghasi@disroot.org/T/

Masoud Aghasi (3):
  bpf: Fix incorrect handling of user flags in bpf_percpu_array_update
  bpf: Fix incorrect handling of user flags by percpu hash map updates
  selftests/bpf: add tests for percpu map flags combination

 include/linux/bpf.h                           |   3 +
 kernel/bpf/arraymap.c                         |   6 +-
 kernel/bpf/hashtab.c                          |  10 +-
 .../selftests/bpf/prog_tests/percpu_alloc.c   | 249 ++++++++++++++++++
 4 files changed, 261 insertions(+), 7 deletions(-)

-- 
2.47.3