Re: [PATCH net v2] net: nexthop: don't allow empty NHA_GROUP

[David Ahern <dsahern@gmail.com>]

On 8/22/20 6:06 AM, Nikolay Aleksandrov wrote:
> Currently the nexthop code will use an empty NHA_GROUP attribute, but it
> requires at least 1 entry in order to function properly. Otherwise we
> end up derefencing null or random pointers all over the place due to not
> having any nh_grp_entry members allocated, nexthop code relies on having at
> least the first member present. Empty NHA_GROUP doesn't make any sense so
> just disallow it.
> Also add a WARN_ON for any future users of nexthop_create_group().
> 

...

> 
> CC: David Ahern <dsahern@gmail.com>
> Fixes: 430a049190de ("nexthop: Add support for nexthop groups")
> Reported-by: syzbot+a61aa19b0c14c8770bd9@syzkaller.appspotmail.com
> Signed-off-by: Nikolay Aleksandrov <nikolay@cumulusnetworks.com>
> ---
> Tested on 5.3 and latest -net by adding a nexthop with an empty NHA_GROUP
> (purposefully broken iproute2) and then adding a route which uses it.
> 
> v2: no changes, include stack trace in commit message
> 
>  net/ipv4/nexthop.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 

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

Thanks, Nik