linux-kernel - Re: linux-next: manual merge of the net-next tree with the net tree

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Date:   Fri, 19 Mar 2021 08:21:15 +0100
From:   Daniel Borkmann <daniel@...earbox.net>
To:     Piotr Krysiuk <piotras@...il.com>
Cc:     David Miller <davem@...emloft.net>,
        Networking <netdev@...r.kernel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux Next Mailing List <linux-next@...r.kernel.org>,
        Yonghong Song <yhs@...com>,
        Stephen Rothwell <sfr@...b.auug.org.au>
Subject: Re: linux-next: manual merge of the net-next tree with the net tree

On 3/19/21 3:11 AM, Piotr Krysiuk wrote:
> Hi Daniel,
> 
> On Fri, Mar 19, 2021 at 12:16 AM Stephen Rothwell <sfr@...b.auug.org.au>
> wrote:
> 
>> diff --cc kernel/bpf/verifier.c
>> index 44e4ec1640f1,f9096b049cd6..000000000000
>> --- a/kernel/bpf/verifier.c
>> +++ b/kernel/bpf/verifier.c
>> @@@ -5876,10 -6056,22 +6060,23 @@@ static int retrieve_ptr_limit(const str
>>                  if (mask_to_left)
>>                          *ptr_limit = MAX_BPF_STACK + off;
>>                  else
>>   -                      *ptr_limit = -off;
>>   -              return 0;
>>   +                      *ptr_limit = -off - 1;
>>   +              return *ptr_limit >= max ? -ERANGE : 0;
>> +       case PTR_TO_MAP_KEY:
>> +               /* Currently, this code is not exercised as the only use
>> +                * is bpf_for_each_map_elem() helper which requires
>> +                * bpf_capble. The code has been tested manually for
>> +                * future use.
>> +                */
>> +               if (mask_to_left) {
>> +                       *ptr_limit = ptr_reg->umax_value + ptr_reg->off;
>> +               } else {
>> +                       off = ptr_reg->smin_value + ptr_reg->off;
>> +                       *ptr_limit = ptr_reg->map_ptr->key_size - off;
>> +               }
>> +               return 0;
>>
> 
> PTR_TO_MAP_VALUE logic above looks like copy-paste of old PTR_TO_MAP_VALUE
> code from before "bpf: Fix off-by-one for area size in creating mask to
> left" and is apparently affected by the same off-by-one, except this time
> on "key_size" area and not "value_size".
> 
> This needs to be fixed in the same way as we did with PTR_TO_MAP_VALUE.
> What is the best way to proceed?

Hm, not sure why PTR_TO_MAP_KEY was added by 69c087ba6225 in the first place, I
presume noone expects this to be used from unprivileged as the comment says.
Resolution should be to remove the PTR_TO_MAP_KEY case entirely from that switch
until we have an actual user.

Thanks,
Daniel