[PATCH bpf-next v2] libbpf: Check for unknown type ID in btf__align_of()

[Abhinav Madake <abhinavmadake@gmail.com>]

btf__align_of() passes the result of btf__type_by_id() to btf_kind()
without a NULL check, so an unknown type ID crashes. Parsed BTF cannot
hit this since btf_sanity_check() rejects dangling references, but BTF
built with btf__add_*() can, as those only check the ID range.

Return 0 with errno set to EINVAL, like the unsupported-kind case.

Link: https://github.com/libbpf/libbpf/issues/983
Signed-off-by: Abhinav Madake <abhinavmadake@gmail.com>
---
v2: return 0 with errno instead of -EINVAL, callers test for 0.

 tools/lib/bpf/btf.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/tools/lib/bpf/btf.c b/tools/lib/bpf/btf.c
index 908bd3442..6bfbc7a65 100644
--- a/tools/lib/bpf/btf.c
+++ b/tools/lib/bpf/btf.c
@@ -986,8 +986,12 @@ done:
 int btf__align_of(const struct btf *btf, __u32 id)
 {
 	const struct btf_type *t = btf__type_by_id(btf, id);
-	__u16 kind = btf_kind(t);
+	__u16 kind;
 
+	if (!t)
+		return errno = EINVAL, 0;
+
+	kind = btf_kind(t);
 	switch (kind) {
 	case BTF_KIND_INT:
 	case BTF_KIND_ENUM:
-- 
2.47.0