netdev - [RFC] netlink: check for NULL attribute in nla_parse_nested

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Date: Thu, 15 Feb 2024 17:52:48 -0800
From: Stephen Hemminger <stephen@...workplumber.org>
To: netdev@...r.kernel.org
Cc: Stephen Hemminger <stephen@...workplumber.org>
Subject: [RFC] netlink: check for NULL attribute in nla_parse_nested_deprecated

Lots of code in network schedulers has the pattern:
	if (!nla) {
		NL_SET_ERR_MSG_MOD(extack, "missing attributes");
		return -EINVAL;
	}

	err = nla_parse_nested_deprecated(tb, TCA_CSUM_MAX, nla, csum_policy,
					  NULL);
	if (err < 0)
		return err;

The check for nla being NULL can be moved into nla_parse_nested_deprecated().
Which simplifies lots of places.

This is safer and won't break other places since:
	err = nla_parse_nested_deprecated(tb, TCA_XXXX, NULL, some_policy, NULL);
would have crashed kernel because nla_parse_deprecated derefences the nla
argument before calling __nla_parse.

Signed-off-by: Stephen Hemminger <stephen@...workplumber.org>
---
 include/net/netlink.h | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/include/net/netlink.h b/include/net/netlink.h
index c19ff921b661..05d137283ab0 100644
--- a/include/net/netlink.h
+++ b/include/net/netlink.h
@@ -1322,6 +1322,11 @@ static inline int nla_parse_nested_deprecated(struct nlattr *tb[], int maxtype,
 					      const struct nla_policy *policy,
 					      struct netlink_ext_ack *extack)
 {
+	if (!nla) {
+		NL_SET_ERR_MSG_MOD(extack, "missing attributes");
+		return -EINVAL;
+	}
+
 	return __nla_parse(tb, maxtype, nla_data(nla), nla_len(nla), policy,
 			   NL_VALIDATE_LIBERAL, extack);
 }
-- 
2.43.0