Hi,
This series fixes a verifier issue with bpf_d_path() and adds a
regression test to cover its use within a hook function.
Patch 1 updates the bpf_d_path() helper prototype so that the second
argument is marked as MEM_WRITE. This makes it explicit to the verifier
that the helper writes into the provided buffer.
Patch 2 extends the existing d_path selftest to cover incorrect verifier
assumptions caused by an incorrect function prototype. The test program calls
bpf_d_path() and checks if the first character of the path is '/'.
It ensures the verifier does not assume the buffer remains unwritten.
Changelog
=========
v4:
- Use the fallocate hook instead of an LSM hook to simplify the selftest,
as suggested by Matt and Alexei.
- Add a utility function in test_d_path.c to load the BPF program,
improving code reuse.
v3:
- Switch the pathname prefix loop to use bpf_for() instead of
#pragma unroll, as suggested by Matt.
- Remove /tmp/bpf_d_path_test in the test cleanup path.
- Add the missing Reviewed-by tags.
v2:
- Merge the new test into the existing d_path selftest rather than
creating new files.
- Add PID filtering in the LSM program to avoid nondeterministic failures
due to unrelated processes triggering bprm_check_security.
- Synchronize child execution using a pipe to ensure deterministic
updates to the PID.
Thanks for your time and reviews.
Shuran Liu (2):
bpf: mark bpf_d_path() buffer as writeable
selftests/bpf: add regression test for bpf_d_path()
kernel/trace/bpf_trace.c | 2 +-
.../testing/selftests/bpf/prog_tests/d_path.c | 90 +++++++++++++++----
.../testing/selftests/bpf/progs/test_d_path.c | 23 +++++
3 files changed, 96 insertions(+), 19 deletions(-)
--
2.52.0
