[PATCH AUTOSEL 5.16 009/217] libbpf: Improve sanity checking during BTF fix up

[Sasha Levin]

From: Andrii Nakryiko <andrii@xxxxxxxxxx>

[ Upstream commit 88918dc12dc357a06d8d722a684617b1c87a4654 ]

If BTF is corrupted DATASEC's variable type ID might be incorrect.
Prevent this easy to detect situation with extra NULL check.
Reported by oss-fuzz project.

Signed-off-by: Andrii Nakryiko <andrii@xxxxxxxxxx>
Signed-off-by: Alexei Starovoitov <ast@xxxxxxxxxx>
Acked-by: Yonghong Song <yhs@xxxxxx>
Link: https://lore.kernel.org/bpf/20211103173213.1376990-3-andrii@xxxxxxxxxx
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 tools/lib/bpf/libbpf.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index b5bf1c074832e..18651e11b9ba3 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -2752,13 +2752,12 @@ static int btf_fixup_datasec(struct bpf_object *obj, struct btf *btf,
 
 	for (i = 0, vsi = btf_var_secinfos(t); i < vars; i++, vsi++) {
 		t_var = btf__type_by_id(btf, vsi->type);
-		var = btf_var(t_var);
-
-		if (!btf_is_var(t_var)) {
+		if (!t_var || !btf_is_var(t_var)) {
 			pr_debug("Non-VAR type seen in section %s\n", name);
 			return -EINVAL;
 		}
 
+		var = btf_var(t_var);
 		if (var->linkage == BTF_VAR_STATIC)
 			continue;
 
-- 
2.34.1