[PATCH bpf 1/2] bpf: enforce returning 0 for fentry/fexit progs

[Yonghong Song <yhs@xxxxxx>]

Currently, tracing/fentry and tracing/fexit prog
return values are not enforced. In trampoline codes,
the fentry/fexit prog return values are ignored.
Let us enforce it to be 0 to avoid confusion and
allows potential future extension.

Fixes: fec56f5890d9 ("bpf: Introduce BPF trampoline")
Signed-off-by: Yonghong Song <yhs@xxxxxx>
---
 kernel/bpf/verifier.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index fa1d8245b925..17b8448babfe 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -7059,6 +7059,13 @@ static int check_return_code(struct bpf_verifier_env *env)
 			return 0;
 		range = tnum_const(0);
 		break;
+	case BPF_PROG_TYPE_TRACING:
+		if (env->prog->expected_attach_type == BPF_TRACE_FENTRY ||
+		    env->prog->expected_attach_type == BPF_TRACE_FEXIT) {
+			range = tnum_const(0);
+			break;
+		}
+		return 0;
 	default:
 		return 0;
 	}
-- 
2.24.1