check bpf_func_state->callback_depth when pruning states

This patch-set fixes bug in states pruning logic hit in mailing list discussion [0]. The details of the fix are in patch #1.

The main idea for the fix belongs to Yonghong Song, mine contribution is merely in review and test cases.

There are some changes in verification performance:

File                       Program        Insns    (DIFF)  States  (DIFF)
-------------------------  -------------  ---------------  --------------
pyperf600_bpf_loop.bpf.o   on_event          +15 (+0.42%)     +0 (+0.00%)
strobemeta_bpf_loop.bpf.o  on_event        +857 (+37.95%)   +60 (+38.96%)
xdp_synproxy_kern.bpf.o    syncookie_tc   +2892 (+30.39%)  +109 (+36.33%)
xdp_synproxy_kern.bpf.o    syncookie_xdp  +2892 (+30.01%)  +109 (+36.09%)

(when tested on a subset of selftests identified by
selftests/bpf/veristat.cfg and Cilium bpf object files from [4])

Changelog:
v2 [2] -> v3:
- fixes for verifier.c commit message as suggested by Yonghong;
- patch-set re-rerouted to 'bpf' tree as suggested in [2];
- patch for test_tcp_custom_syncookie is sent separately to 'bpf-next' [3].
- veristat results updated using 'bpf' tree as baseline and clang 16.

v1 [1] -> v2:
- patch #2 commit message updated to better reflect verifier behavior with regards to checkpoints tree (suggested by Yonghong);
- veristat results added (suggested by Andrii).

[0] https://lore.kernel.org/bpf/[email protected]/
[1] https://lore.kernel.org/bpf/[email protected]/
[2] https://lore.kernel.org/bpf/[email protected]/
[3] https://lore.kernel.org/bpf/[email protected]/
[4] https://github.com/anakryiko/cilium

Eduard Zingerman (2):
bpf: check bpf_func_state->callback_depth when pruning states selftests/bpf: test case for callback_depth states pruning logic

 kernel/bpf/verifier.c                         |  3 +
 .../bpf/progs/verifier_iterating_callbacks.c  | 70 +++++++++++++++++++
 2 files changed, 73 insertions(+)

2.43.0