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

Gustavo A. R. Silva
2025-05-20T23:46:41Z

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@kernel.org>

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

Thanks!
-Gustavo

> ---
> Cc: Kuniyuki Iwashima <kuniyu@amazon.com>
> Cc: Eric Dumazet <edumazet@google.com>
> Cc: Jakub Kicinski <kuba@kernel.org>
> Cc: "David S. Miller" <davem@davemloft.net>
> Cc: Paolo Abeni <pabeni@redhat.com>
> Cc: Simon Horman <horms@kernel.org>
> Cc: Ido Schimmel <idosch@nvidia.com>
> Cc: <netdev@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;