Re: [PATCH] ipv6: route: fix possible null-pointer-dereference in ip6_route_info_create

[David Ahern <dsahern@kernel.org>]

On 10/31/24 9:58 PM, Yi Zou wrote:
> In the ip6_route_info_create function, the variable fib6_nh is
> assigned the return value of nexthop_fib6_nh(rt->nh), which could
> result in fib6_nh being NULL. Immediately after this assignment,

not really. IPv6 can only have nexthops in the IPv6 address family, and
nexthop_mpath_select will never return NULL since `0` is always valid
index if the group exists.


> there is a potential dereference of fib6_nh in the following code:
> if (!ipv6_addr_any(&cfg->fc_prefsrc)) {
>  struct net_device *dev = fib6_nh->fib_nh_dev;
> This lead to a null pointer dereference (NPD) risk if fib6_nh is
> NULL. The issue can be resolved by adding a NULL check before the
> deference line.
> 
> Signed-off-by: Yi Zou <03zouyi09.25@gmail.com>
> ---
>  net/ipv6/route.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/net/ipv6/route.c b/net/ipv6/route.c
> index b4251915585f..919592fa4e64 100644
> --- a/net/ipv6/route.c
> +++ b/net/ipv6/route.c
> @@ -3821,7 +3821,7 @@ static struct fib6_info *ip6_route_info_create(struct fib6_config *cfg,
>  			rt->fib6_flags = RTF_REJECT | RTF_NONEXTHOP;
>  	}
>  
> -	if (!ipv6_addr_any(&cfg->fc_prefsrc)) {
> +	if (!ipv6_addr_any(&cfg->fc_prefsrc) && fib6_nh) {
>  		struct net_device *dev = fib6_nh->fib_nh_dev;
>  
>  		if (!ipv6_chk_addr(net, &cfg->fc_prefsrc, dev, 0)) {