[PATCH bpf-next] bpf: use nla_ok() instead of checking nla_len directly

[Jakub Kicinski <kuba@kernel.org>]

nla_len may also be too short to be sane, in which case after
recent changes nla_len() will return a wrapped value.

Reported-by: syzbot+f43a23b6e622797c7a28@syzkaller.appspotmail.com
Fixes: 172db56d90d2 ("netlink: Return unsigned value for nla_len()")
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
---
CC: martin.lau@linux.dev
CC: daniel@iogearbox.net
CC: john.fastabend@gmail.com
CC: ast@kernel.org
CC: andrii@kernel.org
CC: song@kernel.org
CC: yonghong.song@linux.dev
CC: kpsingh@kernel.org
CC: sdf@google.com
CC: haoluo@google.com
CC: jolsa@kernel.org
CC: keescook@chromium.org
CC: bpf@vger.kernel.org
---
 net/core/filter.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/core/filter.c b/net/core/filter.c
index 6d89a9cf33c9..24061f29c9dd 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -203,7 +203,7 @@ BPF_CALL_3(bpf_skb_get_nlattr_nest, struct sk_buff *, skb, u32, a, u32, x)
 		return 0;
 
 	nla = (struct nlattr *) &skb->data[a];
-	if (nla->nla_len > skb->len - a)
+	if (!nla_ok(nla, skb->len - a))
 		return 0;
 
 	nla = nla_find_nested(nla, x);
-- 
2.43.0