linux-kernel - Re: [PATCH RFC 3/5] rtnetlink: do_setlink: Use sockaddr

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Message-ID: <7a2e5da2-5122-4c73-9a94-20e7f21a26f5@gmail.com>
Date: Tue, 5 Nov 2024 11:59:49 +0100
From: Eric Dumazet <eric.dumazet@...il.com>
To: Kees Cook <kees@...nel.org>, Jakub Kicinski <kuba@...nel.org>
Cc: linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
 linux-hardening@...r.kernel.org
Subject: Re: [PATCH RFC 3/5] rtnetlink: do_setlink: Use sockaddr_storage


On 11/4/24 11:25 PM, Kees Cook wrote:
> Instead of a heap allocation use a stack allocated sockaddr_storage to
> support arbitrary length addr_len value (but bounds check it against the
> maximum address length).
>
> Signed-off-by: Kees Cook <kees@...nel.org>
> ---
>   net/core/rtnetlink.c | 12 ++++--------
>   1 file changed, 4 insertions(+), 8 deletions(-)
>
> diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c
> index f0a520987085..eddd10b74f06 100644
> --- a/net/core/rtnetlink.c
> +++ b/net/core/rtnetlink.c
> @@ -2839,21 +2839,17 @@ static int do_setlink(const struct sk_buff *skb,
>   	}
>   
>   	if (tb[IFLA_ADDRESS]) {
> -		struct sockaddr *sa;
> -		int len;
> +		struct sockaddr_storage addr;
> +		struct sockaddr *sa = (struct sockaddr *)&addr;


We already use too much stack space.


Please move addr into struct rtnl_newlink_tbs ?


>   
> -		len = sizeof(sa_family_t) + max_t(size_t, dev->addr_len,
> -						  sizeof(*sa));
> -		sa = kmalloc(len, GFP_KERNEL);
> -		if (!sa) {
> +		if (dev->addr_len > sizeof(addr.__data)) {
>   			err = -ENOMEM;
>   			goto errout;
>   		}
>   		sa->sa_family = dev->type;
> -		memcpy(sa->sa_data, nla_data(tb[IFLA_ADDRESS]),
> +		memcpy(addr.__data, nla_data(tb[IFLA_ADDRESS]),
>   		       dev->addr_len);
>   		err = dev_set_mac_address_user(dev, sa, extack);
> -		kfree(sa);
>   		if (err)
>   			goto errout;
>   		status |= DO_SETLINK_MODIFIED;