Re: XDP invalid memory access

[David Ahern <dsahern@xxxxxxxxx>]

On 1/15/20 3:31 PM, Vincent Li wrote:
> On Wed, Jan 15, 2020 at 2:21 PM Toke Høiland-Jørgensen <toke@xxxxxxxxxx> wrote:
> 
>> You have to check that you're not reading out of bounds before
>> dereferencing the bytes in the TCP header...
>>
> 
> I have below before the optlen
> 
>    47 /* sanity check needed by the eBPF verifier */
> 
>     48 if ((void *)(tcphdr + 1) > data_end)
> 
>     49 return 0;
> 
> this is not enough, how do I check the out of bounds properly?
> 

options are optional and after 'struct tcphdr' you need to do something
like:

   if ((void *)(tcphdr + 1) + tcphdr->doff > data_end)
       return XDP_....