From: Kees Cook <k...@kernel.org>
Date: Mon, 16 Dec 2024 18:04:45 -0800
> Instead of a heap allocation use a stack allocated struct sockaddr, as
> dev_set_mac_address_user() is the consumer (which uses a classic
> struct sockaddr).
I remember Eric's feedback was to keep using heap instead of stack
because rtnl_newlink() path already uses too much on stack.
> Cap the copy to the minimum address size between
> the incoming address and the traditional sa_data field itself.
>
> Putting "sa" on the stack means it will get a reused stack slot since
> it is smaller than other existing single-scope stack variables (like
> the vfinfo array).
>
> Signed-off-by: Kees Cook <k...@kernel.org>
> ---
> Cc: Eric Dumazet <eduma...@google.com>
> Cc: "David S. Miller" <da...@davemloft.net>
> Cc: Jakub Kicinski <k...@kernel.org>
> Cc: Paolo Abeni <pab...@redhat.com>
> Cc: Ido Schimmel <ido...@nvidia.com>
> Cc: Petr Machata <pe...@nvidia.com>
> Cc: net...@vger.kernel.org
> ---
> net/core/rtnetlink.c | 22 +++++++---------------
> 1 file changed, 7 insertions(+), 15 deletions(-)
>
> diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c
> index ab5f201bf0ab..6da0edc0870d 100644
> --- a/net/core/rtnetlink.c
> +++ b/net/core/rtnetlink.c
> @@ -3048,21 +3048,13 @@ 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;
> - memcpy(sa->sa_data, nla_data(tb[IFLA_ADDRESS]),
> - dev->addr_len);
> - err = dev_set_mac_address_user(dev, sa, extack);
> - kfree(sa);
> + struct sockaddr sa = { };
> +
> + /* dev_set_mac_address_user() uses a true struct sockaddr. */
> + sa.sa_family = dev->type;
> + memcpy(sa.sa_data, nla_data(tb[IFLA_ADDRESS]),
> + min(dev->addr_len, sizeof(sa.sa_data_min)));
> + err = dev_set_mac_address_user(dev, &sa, extack);
> if (err)
> goto errout;
> status |= DO_SETLINK_MODIFIED;
> --
> 2.34.1
