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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>
This commit is contained in:
Andrii Nakryiko 2019-07-19 12:32:42 -07:00 committed by Alexei Starovoitov
parent 8d650cdeda
commit 04efe5911f
1 changed files with 6 additions and 0 deletions
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6
tools/lib/bpf/libbpf.c
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@ -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;
}