linux-kernel - Re: [PATCH net v2] ipv4: don't set IPv6 only flags to IPv4 addresses

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Date:   Mon, 1 Jul 2019 11:19:15 -0600
From:   David Ahern <dsahern@...il.com>
To:     Matteo Croce <mcroce@...hat.com>, netdev@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org,
        "David S. Miller" <davem@...emloft.net>,
        Alexey Kuznetsov <kuznet@....inr.ac.ru>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>
Subject: Re: [PATCH net v2] ipv4: don't set IPv6 only flags to IPv4 addresses

On 7/1/19 11:01 AM, Matteo Croce wrote:
> Avoid the situation where an IPV6 only flag is applied to an IPv4 address:
> 
>     # ip addr add 192.0.2.1/24 dev dummy0 nodad home mngtmpaddr noprefixroute
>     # ip -4 addr show dev dummy0
>     2: dummy0: <BROADCAST,NOARP,UP,LOWER_UP> mtu 1500 qdisc noqueue state UNKNOWN group default qlen 1000
>         inet 192.0.2.1/24 scope global noprefixroute dummy0
>            valid_lft forever preferred_lft forever
> 
> Or worse, by sending a malicious netlink command:
> 
>     # ip -4 addr show dev dummy0
>     2: dummy0: <BROADCAST,NOARP,UP,LOWER_UP> mtu 1500 qdisc noqueue state UNKNOWN group default qlen 1000
>         inet 192.0.2.1/24 scope global nodad optimistic dadfailed home tentative mngtmpaddr noprefixroute stable-privacy dummy0
>            valid_lft forever preferred_lft forever
> 
> Signed-off-by: Matteo Croce <mcroce@...hat.com>
> ---
>  net/ipv4/devinet.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/net/ipv4/devinet.c b/net/ipv4/devinet.c
> index c6bd0f7a020a..c5ebfa199794 100644
> --- a/net/ipv4/devinet.c
> +++ b/net/ipv4/devinet.c
> @@ -62,6 +62,11 @@
>  #include <net/net_namespace.h>
>  #include <net/addrconf.h>
>  
> +#define IPV6ONLY_FLAGS	\
> +		(IFA_F_NODAD | IFA_F_OPTIMISTIC | IFA_F_DADFAILED | \
> +		 IFA_F_HOMEADDRESS | IFA_F_TENTATIVE | \
> +		 IFA_F_MANAGETEMPADDR | IFA_F_STABLE_PRIVACY)
> +
>  static struct ipv4_devconf ipv4_devconf = {
>  	.data = {
>  		[IPV4_DEVCONF_ACCEPT_REDIRECTS - 1] = 1,
> @@ -468,6 +473,9 @@ static int __inet_insert_ifa(struct in_ifaddr *ifa, struct nlmsghdr *nlh,
>  	ifa->ifa_flags &= ~IFA_F_SECONDARY;
>  	last_primary = &in_dev->ifa_list;
>  
> +	/* Don't set IPv6 only flags to IPv4 addresses */
> +	ifa->ifa_flags &= ~IPV6ONLY_FLAGS;
> +
>  	for (ifap = &in_dev->ifa_list; (ifa1 = *ifap) != NULL;
>  	     ifap = &ifa1->ifa_next) {
>  		if (!(ifa1->ifa_flags & IFA_F_SECONDARY) &&
> 

I guess at this point we can fail the address add, so this is the best
option. rtm_to_ifaddr could set a message in extack about invalid flags
- not fail the change, just warn the user that flags will be ignored.

Reviewed-by: David Ahern <dsahern@...il.com>