[PATCH v2] erofs: fix inconsistent per-file compression format

[Yue Hu]

On Wed, 27 Dec 2023 13:06:33 +0800
Gao Xiang <hsiangkao at linux.alibaba.com> wrote:

> EROFS can select compression algorithms on a per-file basis, and each
> per-file compression algorithm needs to be marked in the on-disk
> superblock for initialization.
> 
> However, syzkaller can generate inconsistent crafted images that use
> an unsupported algorithm for specific inodes; thus, an unexpected
> "BUG: kernel NULL pointer dereference" can be raised.
> 
> Fix this by checking against `sbi->available_compr_algs` for each
> compressed inode.  Incorrect !erofs_sb_has_compr_cfgs preset bitmap
> is now fixed together since it was harmless previously.
> 
> Reported-by: <bugreport at ubisectech.com>
> Fixes: 14373711dd54 ("erofs: add on-disk compression configurations")
> Signed-off-by: Gao Xiang <hsiangkao at linux.alibaba.com>

Reviewed-by: Yue Hu <huyue2 at coolpad.com>