libbpf: fix SIGSEGV when BTF loading fails, but .BTF.ext exists

In case when BTF loading fails despite sanitization, but BPF object has
.BTF.ext loaded as well, we free and null obj->btf, but not
obj->btf_ext. This leads to an attempt to relocate .BTF.ext later on
during bpf_object__load(), which assumes obj->btf is present. This leads
to SIGSEGV on null pointer access. Fix bug by freeing and nulling
obj->btf_ext as well.

Signed-off-by: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

1 files changed, 6 insertions, 0 deletions

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 794dd5064ae8..87168f21ef43 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -1500,6 +1500,12 @@ static int bpf_object__sanitize_and_load_btf(struct bpf_object *obj)
                            BTF_ELF_SEC, err);
                 btf__free(obj->btf);
                 obj->btf = NULL;
+                /* btf_ext can't exist without btf, so free it as well */
+                if (obj->btf_ext) {
+                        btf_ext__free(obj->btf_ext);
+                        obj->btf_ext = NULL;
+                }
+
                 if (bpf_object__is_btf_mandatory(obj))
                         return err;
         }