Re: [PATCH bpf-next] bpf: fix bpf_dynptr_slice() to stop return an ERR_PTR.

[Martin KaFai Lau <martin.lau@linux.dev>]

On 8/7/23 10:07 AM, Kui-Feng Lee wrote:
> 
> 
> On 8/4/23 15:26, Martin KaFai Lau wrote:
>> On 8/3/23 4:12 PM, thinker.li@gmail.com wrote:
>>> From: Kui-Feng Lee <thinker.li@gmail.com>
>>>
>>> Verify if the pointer obtained from bpf_xdp_pointer() is either an error or
>>> NULL before returning it.
>>>
>>> The function bpf_dynptr_slice() mistakenly returned an ERR_PTR. Instead of
>>> solely checking for NULL, it should also verify if the pointer returned by
>>> bpf_xdp_pointer() is an error or NULL.
>>>
>>> Reported-by: Dan Carpenter <dan.carpenter@linaro.org>
>>> Closes: 
>>> https://lore.kernel.org/bpf/d1360219-85c3-4a03-9449-253ea905f9d1@moroto.mountain/
>>> Fixes: 66e3a13e7c2c ("bpf: Add bpf_dynptr_slice and bpf_dynptr_slice_rdwr")
>>> Suggested-by: Alexei Starovoitov <alexei.starovoitov@gmail.com>
>>> Signed-off-by: Kui-Feng Lee <thinker.li@gmail.com>
>>> ---
>>>   kernel/bpf/helpers.c | 2 +-
>>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
>>> index 56ce5008aedd..eb91cae0612a 100644
>>> --- a/kernel/bpf/helpers.c
>>> +++ b/kernel/bpf/helpers.c
>>> @@ -2270,7 +2270,7 @@ __bpf_kfunc void *bpf_dynptr_slice(const struct 
>>> bpf_dynptr_kern *ptr, u32 offset
>>>       case BPF_DYNPTR_TYPE_XDP:
>>>       {
>>>           void *xdp_ptr = bpf_xdp_pointer(ptr->data, ptr->offset + offset, len);
>>> -        if (xdp_ptr)
>>> +        if (!IS_ERR_OR_NULL(xdp_ptr))
>>
>> Considering the earlier bpf_dynptr_check_off_len() should have avoided the 
>> IS_ERR() case here, I think targeting bpf-next makes sense. Applied.
> 
> It is a good point. I think the bpf_dynptr_check_off_len() check is
> wrong as well. According to the behavior of the rest of the function,
> it should be
> 
>      err = bpf_dynptr_check_off_len(ptr, ptr->offset + offset, len);

Not sure why it is needed either.
The bpf_dynptr_adjust() has updated the size after updating the offset.
Did I missing other offset update places?