bpf: Fix static checker warning

kernel/bpf/btf.c:4023 btf_distill_func_proto()
        error: potentially dereferencing uninitialized 't'.

kernel/bpf/btf.c
  4012          nargs = btf_type_vlen(func);
  4013          if (nargs >= MAX_BPF_FUNC_ARGS) {
  4014                  bpf_log(log,
  4015                          "The function %s has %d arguments. Too many.\n",
  4016                          tname, nargs);
  4017                  return -EINVAL;
  4018          }
  4019          ret = __get_type_size(btf, func->type, &t);
                                                       ^^
t isn't initialized for the first -EINVAL return

This is unlikely path, since BTF should have been validated at this point.
Fix it by returning 'void' BTF.

Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20191126230106.237179-1-ast@kernel.org

diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index 40efde5..bd5e118 100644 (file)
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -3976,8 +3976,10 @@ static int __get_type_size(struct btf *btf, u32 btf_id,
        t = btf_type_by_id(btf, btf_id);
        while (t && btf_type_is_modifier(t))
                t = btf_type_by_id(btf, t->type);
-       if (!t)
+       if (!t) {
+               *bad_type = btf->types[0];
                return -EINVAL;
+       }
        if (btf_type_is_ptr(t))
                /* kernel size of pointer. Not BPF's size of pointer*/
                return sizeof(void *);