[PATCH 5.2 016/162] libbpf: sanitize VAR to conservative 1-byte INT

Greg Kroah-Hartman
2019-08-27T08:01:54Z

[ Upstream commit 1d4126c4e1190d2f7d3f388552f9bd17ae0c64fc ]

If VAR in non-sanitized BTF was size less than 4, converting such VAR
into an INT with size=4 will cause BTF validation failure due to
violationg of STRUCT (into which DATASEC was converted) member size.
Fix by conservatively using size=1.

Signed-off-by: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
tools/lib/bpf/libbpf.c | 9 +++++++--
1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 3865a5d272514..77e14d9954796 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -1044,8 +1044,13 @@ static void bpf_object__sanitize_btf(struct bpf_object *obj)
if (!has_datasec && kind == BTF_KIND_VAR) {
/* replace VAR with INT */
t->info = BTF_INFO_ENC(BTF_KIND_INT, 0, 0);
- t->size = sizeof(int);
- *(int *)(t+1) = BTF_INT_ENC(0, 0, 32);
+ /*
+ * using size = 1 is the safest choice, 4 will be too
+ * big and cause kernel BTF validation failure if
+ * original variable took less than 4 bytes
+ */
+ t->size = 1;
+ *(int *)(t+1) = BTF_INT_ENC(0, 0, 8);
} else if (!has_datasec && kind == BTF_KIND_DATASEC) {
/* replace DATASEC with STRUCT */
struct btf_var_secinfo *v = (void *)(t + 1);
--
2.20.1