net: limit altnames to 64k total

[ Upstream commit 155fb43b70b5fce341347a77d1af2765d1e8fbb8 ]

Property list (altname is a link "property") is wrapped
in a nlattr. nlattrs length is 16bit so practically
speaking the list of properties can't be longer than
that, otherwise user space would have to interpret
broken netlink messages.

Prevent the problem from occurring by checking the length
of the property list before adding new entries.

Reported-by: George Shuklin <george.shuklin@gmail.com>
Reviewed-by: David Ahern <dsahern@kernel.org>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c
index a8c319dc224a09396fed7af54a3772f485af6390..9c0e8ccf9bc58ec2a90db3beaad72dcb7f5cb300 100644 (file)
--- a/net/core/rtnetlink.c
+++ b/net/core/rtnetlink.c
@@ -3631,12 +3631,23 @@ static int rtnl_alt_ifname(int cmd, struct net_device *dev, struct nlattr *attr,
                           bool *changed, struct netlink_ext_ack *extack)
 {
        char *alt_ifname;
+       size_t size;
        int err;
 
        err = nla_validate(attr, attr->nla_len, IFLA_MAX, ifla_policy, extack);
        if (err)
                return err;
 
+       if (cmd == RTM_NEWLINKPROP) {
+               size = rtnl_prop_list_size(dev);
+               size += nla_total_size(ALTIFNAMSIZ);
+               if (size >= U16_MAX) {
+                       NL_SET_ERR_MSG(extack,
+                                      "effective property list too long");
+                       return -EINVAL;
+               }
+       }
+
        alt_ifname = nla_strdup(attr, GFP_KERNEL_ACCOUNT);
        if (!alt_ifname)
                return -ENOMEM;