[PATCH v3] erofs: fix inconsistent per-file compression format

[Yue Hu]

On Sat, 13 Jan 2024 23:06:02 +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 algorithmtype for specific inodes, e.g. use MicroLZMA
> algorithmtype even it's not set in `sbi->available_compr_algs`.  This
> can lead to an unexpected "BUG: kernel NULL pointer dereference" if
> the corresponding decompressor isn't built-in.
> 
> Fix this by checking against `sbi->available_compr_algs` for each
> m_algorithmformat request.  Incorrect !erofs_sb_has_compr_cfgs preset
> bitmap is now fixed together since it was harmless previously.
> 
> Reported-by: <bugreport at ubisectech.com>
> Fixes: 8f89926290c4 ("erofs: get compression algorithms directly on mapping")
> Fixes: 622ceaddb764 ("erofs: lzma compression support")
> Reviewed-by: Yue Hu <huyue2 at coolpad.com>
> Signed-off-by: Gao Xiang <hsiangkao at linux.alibaba.com>

LGTM.

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