Re: [PATCH] netfilter: ipset: Fix overflow before widen in the bitmap_ip_create() function.

[Gavrilov Ilia]

On 1/11/23 13:19, Simon Horman wrote:
> Hi Gavrilov,
> 
> On Mon, Jan 09, 2023 at 11:54:02AM +0000, Gavrilov Ilia wrote:
>> When first_ip is 0, last_ip is 0xFFFFFFF, and netmask is 31, the value of
>> an arithmetic expression 2 << (netmask - mask_bits - 1) is subject
>> to overflow due to a failure casting operands to a larger data type
>> before performing the arithmetic.
>>
>> Note that it's harmless since the value will be checked at the next step.
> 
> Do you mean 0xFFFFFFFF (8 rather than 8 'F's) ?
> If so, I agree with this patch.
> 

Yes, it's my typo. I meant 0xFFFFFFFF.

>> Found by InfoTeCS on behalf of Linux Verification Center
>> (linuxtesting.org) with SVACE.
>>
>> Fixes: b9fed748185a ("netfilter: ipset: Check and reject crazy /0 input parameters")
>> Signed-off-by: Ilia.Gavrilov <Ilia.Gavrilov@xxxxxxxxxxx>
>> ---
>>   net/netfilter/ipset/ip_set_bitmap_ip.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/net/netfilter/ipset/ip_set_bitmap_ip.c b/net/netfilter/ipset/ip_set_bitmap_ip.c
>> index a8ce04a4bb72..b8f0fb37378f 100644
>> --- a/net/netfilter/ipset/ip_set_bitmap_ip.c
>> +++ b/net/netfilter/ipset/ip_set_bitmap_ip.c
>> @@ -309,7 +309,7 @@ bitmap_ip_create(struct net *net, struct ip_set *set, struct nlattr *tb[],
>>   
>>   		pr_debug("mask_bits %u, netmask %u\n", mask_bits, netmask);
>>   		hosts = 2 << (32 - netmask - 1);
> 
> I think that hosts also overflows, in the case you have described.
> Although it also doesn't matter for the same reason you state.
> But from a correctness point of view perhaps it should also be addressed?
> 


As for 'hosts', the expression "2 << (32 - netmask - 1)" is also subject 
to overflow, but the type of the variable 'hosts' is u32, and the type 
casting gives the correct result. But I will fix it for correctness.


Thank you for review. I will change that in V2.

Ilia.

>> -		elements = 2 << (netmask - mask_bits - 1);
>> +		elements = 2UL << (netmask - mask_bits - 1);
>>   	}
>>   	if (elements > IPSET_BITMAP_MAX_RANGE + 1)
>>   		return -IPSET_ERR_BITMAP_RANGE_SIZE;
>> -- 
>> 2.30.2
>>