Re: [PATCH bpf-next] bpf: Clean code with bpf_copy_to_user

[Tao Chen <chen.dylane@linux.dev>]

在 2025/7/3 23:35, Yonghong Song 写道:
> 
> 
> On 7/3/25 5:43 AM, Tao Chen wrote:
>> No logic change, just use bpf_copy_to_user to clean code.
>>
>> Signed-off-by: Tao Chen <chen.dylane@linux.dev>
>> ---
>>   kernel/bpf/syscall.c | 17 +++--------------
>>   1 file changed, 3 insertions(+), 14 deletions(-)
>>
>> diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
>> index e6eea594f1c..ca152d36312 100644
>> --- a/kernel/bpf/syscall.c
>> +++ b/kernel/bpf/syscall.c
>> @@ -5208,21 +5208,10 @@ static int bpf_task_fd_query_copy(const union 
>> bpf_attr *attr,
>>               if (put_user(zero, ubuf))
>>                   return -EFAULT;
>> -        } else if (input_len >= len + 1) {
>> -            /* ubuf can hold the string with NULL terminator */
>> -            if (copy_to_user(ubuf, buf, len + 1))
>> -                return -EFAULT;
>>           } else {
>> -            /* ubuf cannot hold the string with NULL terminator,
>> -             * do a partial copy with NULL terminator.
>> -             */
>> -            char zero = '\0';
>> -
>> -            err = -ENOSPC;
>> -            if (copy_to_user(ubuf, buf, input_len - 1))
>> -                return -EFAULT;
>> -            if (put_user(zero, ubuf + input_len - 1))
>> -                return -EFAULT;
>> +            err = bpf_copy_to_user(ubuf, buf, input_len, len);
>> +            if (err)
>> +                return err;
>>           }
>>       }
> 
> Actually, there is a return value change with this patch.
> bpf_copy_to_user() return returns -ENOSPC while the original
> implementation may return -EFAULT due to following code.
> 
>          if (put_user(prog_id, &uattr->task_fd_query.prog_id) ||
>              put_user(fd_type, &uattr->task_fd_query.fd_type) ||
>              put_user(probe_offset, &uattr->task_fd_query.probe_offset) ||
>              put_user(probe_addr, &uattr->task_fd_query.probe_addr))
>                  return -EFAULT;
> 
>          return err;
> 

You are right, maybe we can just use:
	err = bpf_copy_to_user(ubuf, buf, input_len, len);
and no return check
or move these put_user code to the front.

-- 
Best Regards
Tao Chen