Re: generic/013 failure to Samba

[ChenXiaoSong <chenxiaosong.chenxiaosong@linux.dev>]

Hi Henrique,

I can reproduce this UBSAN error. You need to compile the kernel code 
using the latest version of Clang.

I would like to give special thanks to Tang Youling 
<tangyouling@kylinos.cn> for his guidance on UBSAN and Clang.

Thanks,
ChenXiaoSong <chenxiaosong@kylinos.cn>

On 12/24/25 23:02, Henrique Carvalho wrote:
> This UBSAN report is consistent with struct copychunk_ioctl_req::Chunks[]
> being annotated with __counted_by_le(ChunkCount) while ChunkCount is not
> set to the allocated capacity before we start populating the array. This is
> the same class of issue described in [1].
> 
> A fix would be to set ChunkCount to chunk_count (capacity) at the start
> of each iteration before accessing Chunks[]. Proposed patch is attached.
> 
> However, if my interpretation is correct, I would expect the first
> population to trip as well since ChunkCount starts at 0, which does not
> happen.
> 
> @Gustavo do you have any insight into why the first access might not
> trigger?
> 
> [1] https://people.kernel.org/gustavoars/how-to-use-the-new-counted_by-attribute-in-c-and-linux
>