[PATCH 7/7] rtnetlink: do_setlink: Use struct sockaddr_storage

[Gustavo A. R. Silva]

On 20/05/25 16:31, Kees Cook wrote:
> 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.
> 
> Signed-off-by: Kees Cook <kees at kernel.org>

Acked-by: Gustavo A. R. Silva <gustavoars at kernel.org>

Thanks!
-Gustavo

> ---
> Cc: Kuniyuki Iwashima <kuniyu at amazon.com>
> Cc: Eric Dumazet <edumazet at google.com>
> Cc: Jakub Kicinski <kuba at kernel.org>
> Cc: "David S. Miller" <davem at davemloft.net>
> Cc: Paolo Abeni <pabeni at redhat.com>
> Cc: Simon Horman <horms at kernel.org>
> Cc: Ido Schimmel <idosch at nvidia.com>
> Cc: <netdev at vger.kernel.org>
> ---
>   net/core/rtnetlink.c | 19 ++++---------------
>   1 file changed, 4 insertions(+), 15 deletions(-)
> 
> diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c
> index 9743f1c2ae3c..f9a35bdc58ad 100644
> --- 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;