From:   "Yichun Zhang (agentzh)" <yichun@openresty.com>
To:     yichun@openresty.com
Cc:     Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Andrii Nakryiko <andrii@kernel.org>,
        Martin KaFai Lau <kafai@fb.com>,
        Song Liu <songliubraving@fb.com>, Yonghong Song <yhs@fb.com>,
        John Fastabend <john.fastabend@gmail.com>,
        KP Singh <kpsingh@kernel.org>,
        Nathan Chancellor <nathan@kernel.org>,
        Nick Desaulniers <ndesaulniers@google.com>,
        netdev@vger.kernel.org, bpf@vger.kernel.org,
        linux-kernel@vger.kernel.org, llvm@lists.linux.dev
Subject: [PATCH] bpf: btf: Fix a var size check in validator
Date:   Fri,  7 Jan 2022 18:22:12 -0800
Message-Id: <20220108022212.962-1-yichun@openresty.com>
Precedence: bulk

The btf validator should croak when the variable size is larger than
its type size, not less. The LLVM optimizer may use smaller sizes for
the C type.

We ran into this issue with real-world BPF programs emitted by the
latest version of Clang/LLVM.

Fixes: 1dc92851849cc ("bpf: kernel side support for BTF Var and DataSec")
Signed-off-by: Yichun Zhang (agentzh) <yichun@openresty.com>
---
 kernel/bpf/btf.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index 9bdb03767db5..2a6967b13ce1 100644
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -3696,7 +3696,7 @@ static int btf_datasec_resolve(struct btf_verifier_env *env,
 			return -EINVAL;
 		}
 
-		if (vsi->size < type_size) {
+		if (vsi->size > type_size) {
 			btf_verifier_log_vsi(env, v->t, vsi, "Invalid size");
 			return -EINVAL;
 		}
-- 
2.17.2