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SubjectRe: linux-next: manual merge of the net-next tree with the net tree
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On 3/19/21 4:33 PM, Alexei Starovoitov wrote:
> On Fri, Mar 19, 2021 at 8:17 AM Yonghong Song <yhs@fb.com> wrote:
>> On 3/19/21 12:21 AM, Daniel Borkmann wrote:
>>> On 3/19/21 3:11 AM, Piotr Krysiuk wrote:
>>>> Hi Daniel,
>>>>
>>>> On Fri, Mar 19, 2021 at 12:16 AM Stephen Rothwell <sfr@canb.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.
>>
>> Alexei suggested so that we don't forget it in the future if
>> bpf_capable() requirement is removed.
>> https://lore.kernel.org/bpf/c837ae55-2487-2f39-47f6-a18781dc6fcc@fb.com/
>>
>> I am okay with either way, fix it or remove it.
>
> I prefer to fix it.

If the bpf_capable() is removed, the verifier would bail out on PTR_TO_MAP_KEY
if not covered in the switch given the recent fixes we did. I can fix it up after
merge if we think bpf_for_each_map_elem() will be used by unpriv in future..

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