[PATCH bpf-next v2 0/2] bpf: Guard conntrack opts error writes

[Yiyang Chen <chenyy23@mails.tsinghua.edu.cn>]

The conntrack lookup/allocation kfuncs expose an opts/opts__sz pair.
The verifier checks the caller-provided opts__sz range, but the wrappers
currently write opts->error after internal errors even when opts__sz is too
small to include that field.

Patch 1 writes opts->error only when opts__sz includes it, and uses a
single helper to fold ERR_PTR returns into the kfunc ABI result while keeping
the local nfct result variable in each wrapper.
Patch 2 adds a bpf_nf regression check that keeps a guard in opts->error
while passing opts__sz covering only netns_id.

The regression check follows the existing bpf_nf test shape.  Before the
fix, the guard is overwritten with -EINVAL even though opts__sz covers only
the first four bytes of the options object.  After the fix, the kfunc still
returns NULL for the invalid size, but the guard remains intact.

Validation, rebased and tested on bpf-next master e771677c937d
("Merge tag 'for-linus-iommufd' of git://git.kernel.org/pub/scm/linux/kernel/git/jgg/iommufd"):

  git diff --check origin/master..HEAD: OK
  scripts/checkpatch.pl --strict on 1/2 and 2/2: OK
  make O=/root/ebpf-verifier-bug-detection/kernel-build/bpf-next \
    net/netfilter/nf_conntrack_bpf.o: OK
  Focused QEMU direct-runner against XDP and TC lookup/alloc paths:
    unpatched bpf-next e771677c937d: guard overwritten with -EINVAL
    patched v2 007dfd0341cd: guard preserved as 0x12345678
  QEMU upstream bpf_nf selftest with CONFIG_NF_CONNTRACK_MARK,
  CONFIG_NF_CONNTRACK_ZONES, and legacy iptables enabled:
    ./test_progs -t bpf_nf -vv: OK
  git am of exported 1/2 and 2/2 on a fresh worktree at base: OK
  range-diff between branch commits and git-am result: equivalent

Changes in v2:
  - Rebased onto current bpf-next master.
  - Reworked patch 1 to use bpf_ct_opts_result() for the ERR_PTR-to-NULL
    conversion and guarded opts->error write, as suggested by Alexei.
  - Kept the local nfct result variable in each wrapper before returning
    through bpf_ct_opts_result().
  - Added matching Fixes tags to the selftest patch so the regression test
    can be backported with the fix.

v1: https://lore.kernel.org/bpf/cover.1781586477.git.chenyy23@mails.tsinghua.edu.cn/

Yiyang Chen (2):
  bpf: Guard conntrack opts error writes
  selftests/bpf: Cover small conntrack opts error writes

 net/netfilter/nf_conntrack_bpf.c              | 35 +++++++------------
 .../testing/selftests/bpf/prog_tests/bpf_nf.c |  6 ++++
 .../testing/selftests/bpf/progs/test_bpf_nf.c | 26 ++++++++++++++
 3 files changed, 45 insertions(+), 22 deletions(-)


base-commit: e771677c937da5808f7b6c1f0e4a97ec1a84f8a8
-- 
2.34.1