Re: [PATCH 2/2] selftests/net: fix uninitialized variables

[John Hubbard <jhubbard@nvidia.com>]

On 5/6/24 11:00 AM, Willem de Bruijn wrote:
> John Hubbard wrote:
...
>> diff --git a/tools/testing/selftests/net/gro.c b/tools/testing/selftests/net/gro.c
>> index 353e1e867fbb..0eb61edaad83 100644
>> --- a/tools/testing/selftests/net/gro.c
>> +++ b/tools/testing/selftests/net/gro.c
>> @@ -110,7 +110,8 @@ static void setup_sock_filter(int fd)
>>   	const int dport_off = tcp_offset + offsetof(struct tcphdr, dest);
>>   	const int ethproto_off = offsetof(struct ethhdr, h_proto);
>>   	int optlen = 0;
>> -	int ipproto_off, opt_ipproto_off;
>> +	int ipproto_off;
>> +	int opt_ipproto_off = 0;
> 
> This is only intended to be used in the case where the IP proto is not TCP:
> 
>                          BPF_STMT(BPF_LD  + BPF_B   + BPF_ABS, ipproto_off),
> +                       BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, IPPROTO_TCP, 2, 0),
> +                       BPF_STMT(BPF_LD  + BPF_B   + BPF_ABS, opt_ipproto_off),
>                          BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, IPPROTO_TCP, 0, 5),
> 
> In that case the test tries again at a different offset that accounts
> for optional IPv6 extension headers.
> 
> This is indeed buggy, in that it might accidentally accept packets
> that should be dropped.
> 
> Initializing to 0 compares against against the first byte of the
> Ethernet header. Which is an external argument to the test. So
> safest is to initialize opt_ipproto_off to ipproto_off and just
> repeat the previous check. Perhaps:
> 
> @@ -118,6 +118,7 @@ static void setup_sock_filter(int fd)
>          else
>                  next_off = offsetof(struct ipv6hdr, nexthdr);
>          ipproto_off = ETH_HLEN + next_off;
> +       opt_ipproto_off = ipproto_off;  /* overridden later if may have exthdrs */

OK, thanks for pointing out the right fix, I'll send a v2 that does that.

thanks,
-- 
John Hubbard
NVIDIA