From: Kumar Kartikeya Dwivedi memxor@gmail.com
[ Upstream commit e68ac0082787f4e8ee6ae5b19076ec7709ce715b ]
When the loader indicates an internal error (result of a checked bpf system call), it returns the result in attr.test.retval. However, tests that rely on ASSERT_OK_PTR on NULL (returned from light skeleton) may miss that NULL denotes an error if errno is set to 0. This would result in skel pointer being NULL, while ASSERT_OK_PTR returning 1, leading to a SEGV on dereference of skel, because libbpf_get_error relies on the assumption that errno is always set in case of error for ptr == NULL.
In particular, this was observed for the ksyms_module test. When executed using `./test_progs -t ksyms`, prior tests manipulated errno and the test didn't crash when it failed at ksyms_module load, while using `./test_progs -t ksyms_module` crashed due to errno being untouched.
Fixes: 67234743736a (libbpf: Generate loader program out of BPF ELF file.) Signed-off-by: Kumar Kartikeya Dwivedi memxor@gmail.com Signed-off-by: Alexei Starovoitov ast@kernel.org Link: https://lore.kernel.org/bpf/20210927145941.1383001-11-memxor@gmail.com Signed-off-by: Sasha Levin sashal@kernel.org --- tools/lib/bpf/skel_internal.h | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-)
diff --git a/tools/lib/bpf/skel_internal.h b/tools/lib/bpf/skel_internal.h index b22b50c1b173e..9cf66702fa8dd 100644 --- a/tools/lib/bpf/skel_internal.h +++ b/tools/lib/bpf/skel_internal.h @@ -105,10 +105,12 @@ static inline int bpf_load_and_run(struct bpf_load_and_run_opts *opts) err = skel_sys_bpf(BPF_PROG_RUN, &attr, sizeof(attr)); if (err < 0 || (int)attr.test.retval < 0) { opts->errstr = "failed to execute loader prog"; - if (err < 0) + if (err < 0) { err = -errno; - else + } else { err = (int)attr.test.retval; + errno = -err; + } goto out; } err = 0;