[bpf,v5,0/2] bpf: fix NULL dereference during extable search

Message

Krister Johansen June 13, 2023, 12:44 a.m. UTC

Hi,
Enclosed are a pair of patches for an oops that can occur if an exception is
generated while a bpf subprogram is running.  One of the bpf_prog_aux entries
for the subprograms are missing an extable.  This can lead to an exception that
would otherwise be handled turning into a NULL pointer bug.

These changes were tested via the verifier and progs selftests and no
regressions were observed.

Changes from v4:
- Ensure that num_exentries is copied to prog->aux from func[0] (Feedback from
  Ilya Leoshkevich)

Changes from v3:
- Selftest style fixups (Feedback from Yonghong Song)
- Selftest needs to assert that test bpf program executed (Feedback from
  Yonghong Song)
- Selftest should combine open and load using open_and_load (Feedback from
  Yonghong Song)

Changes from v2:
- Insert only the main program's kallsyms (Feedback from Yonghong Song and
  Alexei Starovoitov)
- Selftest should use ASSERT instead of CHECK (Feedback from Yonghong Song)
- Selftest needs some cleanup (Feedback from Yonghong Song)
- Switch patch order (Feedback from Alexei Starovoitov)

Changes from v1:
- Add a selftest (Feedback From Alexei Starovoitov)
- Move to a 1-line verifier change instead of searching multiple extables


Krister Johansen (2):
  bpf: ensure main program has an extable
  selftests/bpf: add a test for subprogram extables

 kernel/bpf/verifier.c                         |  7 ++-
 .../bpf/prog_tests/subprogs_extable.c         | 29 +++++++++++
 .../bpf/progs/test_subprogs_extable.c         | 51 +++++++++++++++++++
 3 files changed, 85 insertions(+), 2 deletions(-)
 create mode 100644 tools/testing/selftests/bpf/prog_tests/subprogs_extable.c
 create mode 100644 tools/testing/selftests/bpf/progs/test_subprogs_extable.c