Right now, there is no safe way to use BPF_PROG_TEST_RUN with data_out. This is because bpf_test_finish copies the output buffer to user space without checking its size. This can lead to the kernel overwriting data in user space after the buffer if xdp_adjust_head and friends are in play. Fix this by using bpf_attr.test.data_size_out as a size hint. The old behaviour is retained if size_hint is zero. Interestingly, do_test_single() in test_verifier.c already assumes that this is the intended use of data_size_out, and sets it to the output buffer size. Lorenz Bauer (3): bpf: respect size hint to BPF_PROG_TEST_RUN if present libbpf: require size hint in bpf_prog_test_run selftests: add a test for bpf_prog_test_run output size net/bpf/test_run.c | 9 ++++- tools/lib/bpf/bpf.c | 4 ++- tools/testing/selftests/bpf/test_progs.c | 44 ++++++++++++++++++++++++ 3 files changed, 55 insertions(+), 2 deletions(-) -- 2.17.1
