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 can be read. It ensures the verifier does not assume the buffer remains unwritten.
Changelog =========
v5: - Moved the temporary file for the fallocate test from /tmp to /dev/shm Since bpf CI's 9P filesystem under /tmp does not support fallocate.
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 | 91 +++++++++++++++---- .../testing/selftests/bpf/progs/test_d_path.c | 23 +++++ 3 files changed, 97 insertions(+), 19 deletions(-)