Re: [PATCH] f2fs: reject device aliasing without a multi-device configuration

[Chao Yu]

On 9/18/26 21:39, Seongjae Jeong wrote:
> A malformed F2FS image can enable F2FS_FEATURE_DEVICE_ALIAS without
> providing a multi-device configuration. For a regular single-device
> filesystem, f2fs_scan_devices() returns without allocating sbi->devs.
>
> In this state, f2fs_dev_is_alloc_blocked() passes the device alias
> feature check and dereferences FDEV(0), resulting in a NULL pointer
> dereference during segment allocation.
>
> Device aliasing requires at least one secondary device. Reject
> superblocks that enable device aliasing without entries for both the
> main and secondary devices in sanity_check_raw_super().
>
> Fixes: eae3faf210bd ("f2fs: support dynamic reserve/release for device aliasing")
> Reported-by: syzbot+ae5b8eb92ed40411ce16@xxxxxxxxxxxxxxxxxxxxxxxxx
> Closes: https://syzkaller.appspot.com/bug?extid=ae5b8eb92ed40411ce16
> Signed-off-by: Seongjae Jeong <jsjlee1020@xxxxxxxxx>

Reviewed-by: Chao Yu <chao@xxxxxxxxxx>

Thanks,