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

[Tao Chen]

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@xxxxxxxxx>
> > ---
> >   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