Re: [bug report] selftests/bpf: add trusted global subprog arg tests

On Fri, Aug 9, 2024 at 4:32 AM Dan Carpenter dan.carpenter@linaro.org wrote:

Hello Andrii Nakryiko,

This is a semi-automatic email about new static checker warnings.

Commit c381203eadb7 ("selftests/bpf: add trusted global subprog arg tests") from Jan 29, 2024, leads to the following Smatch complaint:

./tools/testing/selftests/bpf/progs/verifier_global_ptr_args.c:88 trusted_task_arg_nonnull_fail2()
warn: variable dereferenced before check 'nullable' (see line 86)

./tools/testing/selftests/bpf/progs/verifier_global_ptr_args.c 85 /* should fail, PTR_TO_BTF_ID_OR_NULL */ 86 res = subprog_trusted_task_nonnull(nullable); ^^^^^^^^ This is dereferenced

this is intentional, it's testing that verifier will catch this mistake

87
88          if (nullable)
                ^^^^^^^^

NULL check is too late

89                  bpf_task_release(nullable);
90

regards, dan carpenter