Re: [kernel-hardening] Patch for random mac address

[Anisse Astier <anisse@astier.eu>]

On Fri, May 26, 2017 at 09:55:37AM +0200, HacKurx wrote:
> 2017-05-25 19:28 GMT+02:00 Kees Cook <keescook@chromium.org>:
> > How about sending a v2 with that fixed, inline, etc.
> 
> Agree with the V2. I'm not a developer, what do you mean by inline? Send by GIT?
> If someone can make him grow in my place I will pay him a beer ^^

What he meant, is to follow the kernel process for sending patches.
Lukas already sent a link to the documentation, but you may be
interested in these parts:
https://www.kernel.org/doc/html/latest/process/submitting-patches.html#no-mime-no-links-no-compression-no-attachments-just-plain-text
Yes, you can use git as a client (with git send-email), but it's not
mandatory. You should use your real name though:
https://www.kernel.org/doc/html/latest/process/submitting-patches.html#sign-your-work-the-developer-s-certificate-of-origin

And add a Signed-off-by line.


> 
> Thank you all. Best regards,
> 
> HacKurx (Loic)

> diff --git a/net/core/dev.c b/net/core/dev.c
> index fca407b..3eeb42b 100644
> --- a/net/core/dev.c
> +++ b/net/core/dev.c
> @@ -6669,6 +6669,26 @@ int dev_change_flags(struct net_device *dev, unsigned int flags)
>  
>  	changes = (old_flags ^ dev->flags) | (old_gflags ^ dev->gflags);
>  	__dev_notify_flags(dev, old_flags, changes);
> +
> +#ifdef CONFIG_RANDOM_MAC_ADDRESS
> +	if ((changes & IFF_UP) && !(old_flags & IFF_UP)) {
> +		/* randomize MAC whenever interface is brought up */
> +		struct sockaddr sa;
> +		unsigned int mac4;
> +		unsigned short mac2;
> +
> +		mac4 = prandom_u32();
> +		mac2 = prandom_u32();
> +		memcpy(sa.sa_data, &mac4, sizeof(mac4));
> +		memcpy((char *)sa.sa_data + sizeof(mac4), &mac2, sizeof(mac2));
> +		if (!is_valid_ether_addr(sa.sa_data))
> +			sa.sa_data[5] = 1;
> +		sa.sa_data[0] &= 0xFC;
> +		sa.sa_family = dev->type;
> +		dev_set_mac_address(dev, &sa);

You didn't answer my question regarding why this is different from the
function eth_random_addr.

Regards,

Anisse