Merge branch 'net-introduce-nlmsg_payload-helper'

Breno Leitao says:

====================
net: Introduce nlmsg_payload helper

In the current codebase, there are multiple instances where the
structure size is checked before assigning it to a Netlink message. This
check is crucial for ensuring that the structure is correctly mapped
onto the Netlink message, providing a layer of security.

To streamline this process, Jakub Kicinski suggested creating a helper
function, `nlmsg_payload`, which verifies if the structure fits within
the message. If it does, the function returns the data; otherwise, it
returns NULL. This approach simplifies the code and reduces redundancy.

This patchset introduces the `nlmsg_payload` helper and updates several
parts of the code to use it. Further updates will follow in subsequent
patchsets.

v1: https://lore.kernel.org/20250411-nlmsg-v1-0-ddd4e065cb15@debian.org
====================

Link: https://patch.msgid.link/20250414-nlmsg-v2-0-3d90cb42c6af@debian.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

6 files changed, 38 insertions, 20 deletions

diff --git a/include/net/netlink.h b/include/net/netlink.h
index 29e0db940382..82e07e272290 100644
--- a/include/net/netlink.h
+++ b/include/net/netlink.h
@@ -612,6 +612,22 @@ static inline int nlmsg_len(const struct nlmsghdr *nlh)
 }
 
 /**
+ * nlmsg_payload - message payload if the data fits in the len
+ * @nlh: netlink message header
+ * @len: struct length
+ *
+ * Returns: The netlink message payload/data if the length is sufficient,
+ * otherwise NULL.
+ */
+static inline void *nlmsg_payload(const struct nlmsghdr *nlh, size_t len)
+{
+	if (nlh->nlmsg_len < nlmsg_msg_size(len))
+		return NULL;
+
+	return nlmsg_data(nlh);
+}
+
+/**
  * nlmsg_attrdata - head of attributes data
  * @nlh: netlink message header
  * @hdrlen: length of family specific header
diff --git a/net/core/fib_rules.c b/net/core/fib_rules.c
index 4bc64d912a1c..06052b6c946b 100644
--- a/net/core/fib_rules.c
+++ b/net/core/fib_rules.c
@@ -852,13 +852,14 @@ int fib_newrule(struct net *net, struct sk_buff *skb, struct nlmsghdr *nlh,
 		struct netlink_ext_ack *extack, bool rtnl_held)
 {
 	struct fib_rule *rule = NULL, *r, *last = NULL;
-	struct fib_rule_hdr *frh = nlmsg_data(nlh);
 	int err = -EINVAL, unresolved = 0;
 	struct fib_rules_ops *ops = NULL;
 	struct nlattr *tb[FRA_MAX + 1];
 	bool user_priority = false;
+	struct fib_rule_hdr *frh;
 
-	if (nlh->nlmsg_len < nlmsg_msg_size(sizeof(*frh))) {
+	frh = nlmsg_payload(nlh, sizeof(*frh));
+	if (!frh) {
 		NL_SET_ERR_MSG(extack, "Invalid msg length");
 		goto errout;
 	}
@@ -980,13 +981,14 @@ int fib_delrule(struct net *net, struct sk_buff *skb, struct nlmsghdr *nlh,
 		struct netlink_ext_ack *extack, bool rtnl_held)
 {
 	struct fib_rule *rule = NULL, *nlrule = NULL;
-	struct fib_rule_hdr *frh = nlmsg_data(nlh);
 	struct fib_rules_ops *ops = NULL;
 	struct nlattr *tb[FRA_MAX+1];
 	bool user_priority = false;
+	struct fib_rule_hdr *frh;
 	int err = -EINVAL;
 
-	if (nlh->nlmsg_len < nlmsg_msg_size(sizeof(*frh))) {
+	frh = nlmsg_payload(nlh, sizeof(*frh));
+	if (!frh) {
 		NL_SET_ERR_MSG(extack, "Invalid msg length");
 		goto errout;
 	}
@@ -1238,12 +1240,12 @@ static int fib_valid_dumprule_req(const struct nlmsghdr *nlh,
 {
 	struct fib_rule_hdr *frh;
 
-	if (nlh->nlmsg_len < nlmsg_msg_size(sizeof(*frh))) {
+	frh = nlmsg_payload(nlh, sizeof(*frh));
+	if (!frh) {
 		NL_SET_ERR_MSG(extack, "Invalid header for fib rule dump request");
 		return -EINVAL;
 	}
 
-	frh = nlmsg_data(nlh);
 	if (frh->dst_len || frh->src_len || frh->tos || frh->table ||
 	    frh->res1 || frh->res2 || frh->action || frh->flags) {
 		NL_SET_ERR_MSG(extack,
diff --git a/net/core/neighbour.c b/net/core/neighbour.c
index a07249b59ae1..65cf582b5dac 100644
--- a/net/core/neighbour.c
+++ b/net/core/neighbour.c
@@ -2430,12 +2430,12 @@ static int neightbl_valid_dump_info(const struct nlmsghdr *nlh,
 {
 	struct ndtmsg *ndtm;
 
-	if (nlh->nlmsg_len < nlmsg_msg_size(sizeof(*ndtm))) {
+	ndtm = nlmsg_payload(nlh, sizeof(*ndtm));
+	if (!ndtm) {
 		NL_SET_ERR_MSG(extack, "Invalid header for neighbor table dump request");
 		return -EINVAL;
 	}
 
-	ndtm = nlmsg_data(nlh);
 	if (ndtm->ndtm_pad1  || ndtm->ndtm_pad2) {
 		NL_SET_ERR_MSG(extack, "Invalid values in header for neighbor table dump request");
 		return -EINVAL;
@@ -2855,12 +2855,12 @@ static int neigh_valid_get_req(const struct nlmsghdr *nlh,
 	struct ndmsg *ndm;
 	int err, i;
 
-	if (nlh->nlmsg_len < nlmsg_msg_size(sizeof(*ndm))) {
+	ndm = nlmsg_payload(nlh, sizeof(*ndm));
+	if (!ndm) {
 		NL_SET_ERR_MSG(extack, "Invalid header for neighbor get request");
 		return -EINVAL;
 	}
 
-	ndm = nlmsg_data(nlh);
 	if (ndm->ndm_pad1  || ndm->ndm_pad2  || ndm->ndm_state ||
 	    ndm->ndm_type) {
 		NL_SET_ERR_MSG(extack, "Invalid values in header for neighbor get request");
diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c
index 38526210b8fd..f5c018090efc 100644
--- a/net/core/rtnetlink.c
+++ b/net/core/rtnetlink.c
@@ -4887,12 +4887,12 @@ static int valid_fdb_dump_strict(const struct nlmsghdr *nlh,
 	struct ndmsg *ndm;
 	int err, i;
 
-	if (nlh->nlmsg_len < nlmsg_msg_size(sizeof(*ndm))) {
+	ndm = nlmsg_payload(nlh, sizeof(*ndm));
+	if (!ndm) {
 		NL_SET_ERR_MSG(extack, "Invalid header for fdb dump request");
 		return -EINVAL;
 	}
 
-	ndm = nlmsg_data(nlh);
 	if (ndm->ndm_pad1  || ndm->ndm_pad2  || ndm->ndm_state ||
 	    ndm->ndm_flags || ndm->ndm_type) {
 		NL_SET_ERR_MSG(extack, "Invalid values in header for fdb dump request");
diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
index 9ba83f0c9928..4af276179542 100644
--- a/net/ipv6/addrconf.c
+++ b/net/ipv6/addrconf.c
@@ -5346,12 +5346,12 @@ static int inet6_valid_dump_ifaddr_req(const struct nlmsghdr *nlh,
 	struct ifaddrmsg *ifm;
 	int err, i;
 
-	if (nlh->nlmsg_len < nlmsg_msg_size(sizeof(*ifm))) {
+	ifm = nlmsg_payload(nlh, sizeof(*ifm));
+	if (!ifm) {
 		NL_SET_ERR_MSG_MOD(extack, "Invalid header for address dump request");
 		return -EINVAL;
 	}
 
-	ifm = nlmsg_data(nlh);
 	if (ifm->ifa_prefixlen || ifm->ifa_flags || ifm->ifa_scope) {
 		NL_SET_ERR_MSG_MOD(extack, "Invalid values in header for address dump request");
 		return -EINVAL;
@@ -5484,7 +5484,8 @@ static int inet6_rtm_valid_getaddr_req(struct sk_buff *skb,
 	struct ifaddrmsg *ifm;
 	int i, err;
 
-	if (nlh->nlmsg_len < nlmsg_msg_size(sizeof(*ifm))) {
+	ifm = nlmsg_payload(nlh, sizeof(*ifm));
+	if (!ifm) {
 		NL_SET_ERR_MSG_MOD(extack, "Invalid header for get address request");
 		return -EINVAL;
 	}
@@ -5493,7 +5494,6 @@ static int inet6_rtm_valid_getaddr_req(struct sk_buff *skb,
 		return nlmsg_parse_deprecated(nlh, sizeof(*ifm), tb, IFA_MAX,
 					      ifa_ipv6_policy, extack);
 
-	ifm = nlmsg_data(nlh);
 	if (ifm->ifa_prefixlen || ifm->ifa_flags || ifm->ifa_scope) {
 		NL_SET_ERR_MSG_MOD(extack, "Invalid values in header for get address request");
 		return -EINVAL;
diff --git a/net/mpls/af_mpls.c b/net/mpls/af_mpls.c
index 1f63b32d76d6..d536c97144e9 100644
--- a/net/mpls/af_mpls.c
+++ b/net/mpls/af_mpls.c
@@ -2095,12 +2095,12 @@ static int mpls_valid_fib_dump_req(struct net *net, const struct nlmsghdr *nlh,
 	struct rtmsg *rtm;
 	int err, i;
 
-	if (nlh->nlmsg_len < nlmsg_msg_size(sizeof(*rtm))) {
+	rtm = nlmsg_payload(nlh, sizeof(*rtm));
+	if (!rtm) {
 		NL_SET_ERR_MSG_MOD(extack, "Invalid header for FIB dump request");
 		return -EINVAL;
 	}
 
-	rtm = nlmsg_data(nlh);
 	if (rtm->rtm_dst_len || rtm->rtm_src_len  || rtm->rtm_tos   ||
 	    rtm->rtm_table   || rtm->rtm_scope    || rtm->rtm_type  ||
 	    rtm->rtm_flags) {
@@ -2288,7 +2288,8 @@ static int mpls_valid_getroute_req(struct sk_buff *skb,
 	struct rtmsg *rtm;
 	int i, err;
 
-	if (nlh->nlmsg_len < nlmsg_msg_size(sizeof(*rtm))) {
+	rtm = nlmsg_payload(nlh, sizeof(*rtm));
+	if (!rtm) {
 		NL_SET_ERR_MSG_MOD(extack,
 				   "Invalid header for get route request");
 		return -EINVAL;
@@ -2298,7 +2299,6 @@ static int mpls_valid_getroute_req(struct sk_buff *skb,
 		return nlmsg_parse_deprecated(nlh, sizeof(*rtm), tb, RTA_MAX,
 					      rtm_mpls_policy, extack);
 
-	rtm = nlmsg_data(nlh);
 	if ((rtm->rtm_dst_len && rtm->rtm_dst_len != 20) ||
 	    rtm->rtm_src_len || rtm->rtm_tos || rtm->rtm_table ||
 	    rtm->rtm_protocol || rtm->rtm_scope || rtm->rtm_type) {