In the vlan_changelink function, a loop is used to parse the nested
attributes IFLA_VLAN_EGRESS_QOS and IFLA_VLAN_INGRESS_QOS in order to
obtain the struct ifla_vlan_qos_mapping. These two nested attributes are
checked in the vlan_validate_qos_map function, which calls
nla_validate_nested_deprecated with the vlan_map_policy.

However, this deprecated validator applies a LIBERAL strictness, allowing
the presence of an attribute with the type IFLA_VLAN_QOS_UNSPEC.
Consequently, the loop in vlan_changelink may parse an attribute of type
IFLA_VLAN_QOS_UNSPEC and believe it carries a payload of
struct ifla_vlan_qos_mapping, which is not necessarily true.

To address this issue and ensure compatibility, this patch introduces two
type checks that skip attributes whose type is not IFLA_VLAN_QOS_MAPPING.

Fixes: 07b5b17e157b ("[VLAN]: Use rtnl_link API")
Signed-off-by: Lin Ma <linma@zju.edu.cn>
---
V1 -> V2: make net-next to net as suggested by Paolo
          and add Fixes tag for this one

 net/8021q/vlan_netlink.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/net/8021q/vlan_netlink.c b/net/8021q/vlan_netlink.c
index 214532173536..a3b68243fd4b 100644
--- a/net/8021q/vlan_netlink.c
+++ b/net/8021q/vlan_netlink.c
@@ -118,12 +118,16 @@ static int vlan_changelink(struct net_device *dev, struct nlattr *tb[],
 	}
 	if (data[IFLA_VLAN_INGRESS_QOS]) {
 		nla_for_each_nested(attr, data[IFLA_VLAN_INGRESS_QOS], rem) {
+			if (nla_type(attr) != IFLA_VLAN_QOS_MAPPING)
+				continue;
 			m = nla_data(attr);
 			vlan_dev_set_ingress_priority(dev, m->to, m->from);
 		}
 	}
 	if (data[IFLA_VLAN_EGRESS_QOS]) {
 		nla_for_each_nested(attr, data[IFLA_VLAN_EGRESS_QOS], rem) {
+			if (nla_type(attr) != IFLA_VLAN_QOS_MAPPING)
+				continue;
 			m = nla_data(attr);
 			err = vlan_dev_set_egress_priority(dev, m->from, m->to);
 			if (err)
-- 
2.17.1

On Thu, Jan 18, 2024 at 09:03:06PM +0800, Lin Ma wrote:
> In the vlan_changelink function, a loop is used to parse the nested
> attributes IFLA_VLAN_EGRESS_QOS and IFLA_VLAN_INGRESS_QOS in order to
> obtain the struct ifla_vlan_qos_mapping. These two nested attributes are
> checked in the vlan_validate_qos_map function, which calls
> nla_validate_nested_deprecated with the vlan_map_policy.
> 
> However, this deprecated validator applies a LIBERAL strictness, allowing
> the presence of an attribute with the type IFLA_VLAN_QOS_UNSPEC.
> Consequently, the loop in vlan_changelink may parse an attribute of type
> IFLA_VLAN_QOS_UNSPEC and believe it carries a payload of
> struct ifla_vlan_qos_mapping, which is not necessarily true.
> 
> To address this issue and ensure compatibility, this patch introduces two
> type checks that skip attributes whose type is not IFLA_VLAN_QOS_MAPPING.
> 
> Fixes: 07b5b17e157b ("[VLAN]: Use rtnl_link API")
> Signed-off-by: Lin Ma <linma@zju.edu.cn>
> ---
> V1 -> V2: make net-next to net as suggested by Paolo
>           and add Fixes tag for this one

Reviewed-by: Simon Horman <horms@kernel.org>