Subject: Re: [PATCH net-next] genetlink: do not parse attributes for families with zero maxattr

From: Jiri Pirko <[email-masked]>
Date: Thu, 10 Oct 2019 11:31:53 +0200

Wed, Oct 09, 2019 at 06:44:32PM CEST, [email-masked] wrote:
>Commit c10e6cf85e7d ("net: genetlink: push attrbuf allocation and parsing
>to a separate function") moved attribute buffer allocation and attribute
>parsing from genl_family_rcv_msg_doit() into a separate function
>genl_family_rcv_msg_attrs_parse() which, unlike the previous code, calls
>__nlmsg_parse() even if family->maxattr is 0 (i.e. the family does its own
>parsing). The parser error is ignored and does not propagate out of
>genl_family_rcv_msg_attrs_parse() but an error message ("Unknown attribute
>type") is set in extack and if further processing generates no error or
>warning, it stays there and is interpreted as a warning by userspace.
>
>Dumpit requests are not affected as genl_family_rcv_msg_dumpit() bypasses
>the call of genl_family_rcv_msg_doit() if family->maxattr is zero. Do the
>same also in genl_family_rcv_msg_doit().
>
>Fixes: c10e6cf85e7d ("net: genetlink: push attrbuf allocation and parsing to a separate function")
>Signed-off-by: Michal Kubecek <[email-masked]>
>---
> net/netlink/genetlink.c | 6 ++++--
> 1 file changed, 4 insertions(+), 2 deletions(-)
>
>diff --git a/net/netlink/genetlink.c b/net/netlink/genetlink.c
>index ecc2bd3e73e4..c4bf8830eedf 100644
>--- a/net/netlink/genetlink.c
>+++ b/net/netlink/genetlink.c
>@@ -639,21 +639,23 @@ static int genl_family_rcv_msg_doit(const struct genl_family *family,
> 				    const struct genl_ops *ops,
> 				    int hdrlen, struct net *net)
> {
>-	struct nlattr **attrbuf;
>+	struct nlattr **attrbuf = NULL;
> 	struct genl_info info;
> 	int err;
> 
> 	if (!ops->doit)
> 		return -EOPNOTSUPP;
> 
>+	if (!family->maxattr)
>+		goto no_attrs;
> 	attrbuf = genl_family_rcv_msg_attrs_parse(family, nlh, extack,
> 						  ops, hdrlen,
> 						  GENL_DONT_VALIDATE_STRICT,
>-						  family->maxattr &&
> 						  family->parallel_ops);

Please also adjust genl_family_rcv_msg_attrs_free() call arg
below in this function in the similar way.

> 	if (IS_ERR(attrbuf))
> 		return PTR_ERR(attrbuf);
> 
>+no_attrs:
> 	info.snd_seq = nlh->nlmsg_seq;
> 	info.snd_portid = NETLINK_CB(skb).portid;
> 	info.nlhdr = nlh;
>-- 
>2.23.0
>