Re: [PATCH] bcachefs: fix shift oob in alloc_lru_idx_fragmentation

[Alan Huang]

On Oct 21, 2024, at 22:09, Jeongjun Park <aha310510@xxxxxxxxx> wrote:
> 
> The size of a.data_type is set abnormally large, causing shift-out-of-bounds.
> To fix this, we need to add validation on a.data_type in 
> alloc_lru_idx_fragmentation().
> 
> Reported-by: syzbot+7f45fa9805c40db3f108@xxxxxxxxxxxxxxxxxxxxxxxxx
> Fixes: 260af1562ec1 ("bcachefs: Kill alloc_v4.fragmentation_lru")
> Signed-off-by: Jeongjun Park <aha310510@xxxxxxxxx>
> ---
> fs/bcachefs/alloc_background.h       | 3 +++
> fs/bcachefs/disk_accounting_format.h | 2 ++
> 2 files changed, 5 insertions(+)
> 
> diff --git a/fs/bcachefs/alloc_background.h b/fs/bcachefs/alloc_background.h
> index f8e87c6721b1..66a334e2edcd 100644
> --- a/fs/bcachefs/alloc_background.h
> +++ b/fs/bcachefs/alloc_background.h
> @@ -168,6 +168,9 @@ static inline bool data_type_movable(enum bch_data_type type)
> static inline u64 alloc_lru_idx_fragmentation(struct bch_alloc_v4 a,
>   struct bch_dev *ca)
> {
> + if (a.data_type > BCH_DATA_TYPE_MAX)
> + return 0;
> + 
> if (!data_type_movable(a.data_type) ||
>    !bch2_bucket_sectors_fragmented(ca, a))
> return 0;
> diff --git a/fs/bcachefs/disk_accounting_format.h b/fs/bcachefs/disk_accounting_format.h
> index 7b6e6c97e6aa..0232bc9f590d 100644
> --- a/fs/bcachefs/disk_accounting_format.h
> +++ b/fs/bcachefs/disk_accounting_format.h
> @@ -72,6 +72,8 @@ enum bch_data_type {
> BCH_DATA_NR
> };
> 
> +#define BCH_DATA_TYPE_MAX 10

Use BCH_DATA_NR instead.

> +
> static inline bool data_type_is_empty(enum bch_data_type type)
> {
> switch (type) {
> --
>