netdev - [PATCH bpf-next] bpf: fix static checker warning

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Date:   Tue, 26 Nov 2019 15:01:06 -0800
From:   Alexei Starovoitov <ast@...nel.org>
To:     <davem@...emloft.net>
CC:     <daniel@...earbox.net>, <dan.carpenter@...cle.com>,
        <netdev@...r.kernel.org>, <bpf@...r.kernel.org>,
        <kernel-team@...com>
Subject: [PATCH bpf-next] 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@...cle.com>
Signed-off-by: Alexei Starovoitov <ast@...nel.org>
---
 kernel/bpf/btf.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index 40efde5eedcb..bd5e11881ba3 100644
--- 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 *);
-- 
2.23.0