[PATCH net-next v2] genetlink: do not parse attributes for families with zero maxattr

From: Michal Kubecek
Date: Thu Oct 10 2019 - 06:34:06 EST

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 <mkubecek@xxxxxxx>
net/netlink/genetlink.c | 9 +++++----
1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/net/netlink/genetlink.c b/net/netlink/genetlink.c
index ecc2bd3e73e4..1f14e55ad3ad 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)

+ if (!family->maxattr)
+ goto no_attrs;
attrbuf = genl_family_rcv_msg_attrs_parse(family, nlh, extack,
ops, hdrlen,
- family->maxattr &&
if (IS_ERR(attrbuf))
return PTR_ERR(attrbuf);

info.snd_seq = nlh->nlmsg_seq;
info.snd_portid = NETLINK_CB(skb).portid;
info.nlhdr = nlh;
@@ -676,8 +678,7 @@ static int genl_family_rcv_msg_doit(const struct genl_family *family,
family->post_doit(ops, skb, &info);

- genl_family_rcv_msg_attrs_free(family, attrbuf,
- family->maxattr && family->parallel_ops);
+ genl_family_rcv_msg_attrs_free(family, attrbuf, family->parallel_ops);

return err;