Re: [PATCH bpf-next v1 08/13] bpf: Use memmove for bpf_dynptr_{read,write}

Joanne Koong
2022-10-21T18:12:17Z

On Tue, Oct 18, 2022 at 6:59 AM Kumar Kartikeya Dwivedi
<memxor@gmail.com> wrote:
>
> It may happen that destination buffer memory overlaps with memory dynptr
> points to. Hence, we must use memmove to correctly copy from dynptr to
> destination buffer, or source buffer to dynptr.
>
> This actually isn't a problem right now, as memcpy implementation falls
> back to memmove on detecting overlap and warns about it, but we
> shouldn't be relying on that.
>
> Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>

Acked-by: Joanne Koong <joannelkoong@gmail.com>

> ---
> kernel/bpf/helpers.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
> index 0a4017eb3616..2dc3f5ce8f9b 100644
> --- a/kernel/bpf/helpers.c
> +++ b/kernel/bpf/helpers.c
> @@ -1489,7 +1489,7 @@ BPF_CALL_5(bpf_dynptr_read, void *, dst, u32, len, const struct bpf_dynptr_kern
> if (err)
> return err;
>
> - memcpy(dst, src->data + src->offset + offset, len);
> + memmove(dst, src->data + src->offset + offset, len);
>
> return 0;
> }
> @@ -1517,7 +1517,7 @@ BPF_CALL_5(bpf_dynptr_write, const struct bpf_dynptr_kern *, dst, u32, offset, v
> if (err)
> return err;
>
> - memcpy(dst->data + dst->offset + offset, src, len);
> + memmove(dst->data + dst->offset + offset, src, len);
>
> return 0;
> }
> --
> 2.38.0
>