[PATCH v2] erofs/zmap.c: Fix incorrect offset calculation

[Chao Yu]

On 2022/12/9 18:21, Siddh Raman Pant wrote:
> Effective offset to add to length was being incorrectly calculated,
> which resulted in iomap->length being set to 0, triggering a WARN_ON
> in iomap_iter_done().
> 
> Fix that, and describe it in comments.
> 
> This was reported as a crash by syzbot under an issue about a warning
> encountered in iomap_iter_done(), but unrelated to erofs.
> 
> C reproducer: https://syzkaller.appspot.com/text?tag=ReproC&x=1037a6b2880000
> Kernel config: https://syzkaller.appspot.com/text?tag=KernelConfig&x=e2021a61197ebe02
> Dashboard link: https://syzkaller.appspot.com/bug?extid=a8e049cd3abd342936b6
> 
> Reported-by: syzbot+a8e049cd3abd342936b6 at syzkaller.appspotmail.com
> Suggested-by: Gao Xiang <hsiangkao at linux.alibaba.com>
> Signed-off-by: Siddh Raman Pant <code at siddh.me>

Reviewed-by: Chao Yu <chao at kernel.org>

Thanks,