rtnetlink: do_setlink: Use struct sockaddr_storage

Instead of a heap allocating a variably sized struct sockaddr and lying
about the type in the call to netif_set_mac_address(), use a stack
allocated struct sockaddr_storage. This lets us drop the cast and avoid
the allocation.

Putting "ss" on the stack means it will get a reused stack slot since
it is the same size (128B) as other existing single-scope stack variables,
like the vfinfo array (128B), so no additional stack space is used by
this function.

Acked-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Signed-off-by: Kees Cook <kees@kernel.org>
Link: https://patch.msgid.link/20250521204619.2301870-7-kees@kernel.org
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c
index 9743f1c2ae3c34a17b818f311407917d1442806b..f9a35bdc58ad2a6c7d2aa023bef9b48f72336bbc 100644 (file)
--- a/net/core/rtnetlink.c
+++ b/net/core/rtnetlink.c
@@ -3080,17 +3080,7 @@ static int do_setlink(const struct sk_buff *skb, struct net_device *dev,
        }
 
        if (tb[IFLA_ADDRESS]) {
-               struct sockaddr *sa;
-               int len;
-
-               len = sizeof(sa_family_t) + max_t(size_t, dev->addr_len,
-                                                 sizeof(*sa));
-               sa = kmalloc(len, GFP_KERNEL);
-               if (!sa) {
-                       err = -ENOMEM;
-                       goto errout;
-               }
-               sa->sa_family = dev->type;
+               struct sockaddr_storage ss = { };
 
                netdev_unlock_ops(dev);
 
@@ -3098,10 +3088,9 @@ static int do_setlink(const struct sk_buff *skb, struct net_device *dev,
                down_write(&dev_addr_sem);
                netdev_lock_ops(dev);
 
-               memcpy(sa->sa_data, nla_data(tb[IFLA_ADDRESS]),
-                      dev->addr_len);
-               err = netif_set_mac_address(dev, (struct sockaddr_storage *)sa, extack);
-               kfree(sa);
+               ss.ss_family = dev->type;
+               memcpy(ss.__data, nla_data(tb[IFLA_ADDRESS]), dev->addr_len);
+               err = netif_set_mac_address(dev, &ss, extack);
                if (err) {
                        up_write(&dev_addr_sem);
                        goto errout;