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

[Kui-Feng Lee <sinquersw@gmail.com>]

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);

How do you think?