Re: [PATCH v1] ipv4: add iPv4_is_multicast() check in ip_mc_leave_group().

[Nikolay Aleksandrov <nikolay@nvidia.com>]

On 19/01/2021 06:39, Jakub Kicinski wrote:
> On Sun, 17 Jan 2021 05:34:16 -0800 wangyingjie55@126.com wrote:
>> From: Yingjie Wang <wangyingjie55@126.com>
>>
>> There is no iPv4_is_multicast() check added to ip_mc_leave_group()
>> to check if imr->imr_multiaddr.s_addr is a multicast address.
>> If not a multicast address, it may result in an error.
> 
> Could you please say more? From looking at the code it seems like
> no address should match if group is non-mcast, and -EADDRNOTAVAIL 
> will be returned.
> 
> Adding Nik to CC.
> 

Thanks, and absolutely right. I don't see any point in changing the code, also
you are definitely not fixing any bug. 

>> In some cases, the callers of ip_mc_leave_group() don't check
>> whether it is multicast address or not before calling
>> such as do_ip_setsockopt(). So I suggest adding the ipv4_is_multicast()
>> check to the ip_mc_leave_group() to prevent this from happening.
>>
>> Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
>> Signed-off-by: Yingjie Wang <wangyingjie55@126.com>
>> ---
>>  net/ipv4/igmp.c | 3 +++
>>  1 file changed, 3 insertions(+)
>>
>> diff --git a/net/ipv4/igmp.c b/net/ipv4/igmp.c
>> index 7b272bbed2b4..1b6f91271cfd 100644
>> --- a/net/ipv4/igmp.c
>> +++ b/net/ipv4/igmp.c
>> @@ -2248,6 +2248,9 @@ int ip_mc_leave_group(struct sock *sk, struct ip_mreqn *imr)
>>  	u32 ifindex;
>>  	int ret = -EADDRNOTAVAIL;
>>  
>> +	if (!ipv4_is_multicast(group))
>> +		return -EINVAL;
>> +
>>  	ASSERT_RTNL();
>>  
>>  	in_dev = ip_mc_find_dev(net, imr);
>