[PATCH v3] bcachefs: fix shift oob in alloc_lru_idx_fragmentation

[Jeongjun Park]

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 +++
 1 file changed, 3 insertions(+)

diff --git a/fs/bcachefs/alloc_background.h b/fs/bcachefs/alloc_background.h
index f8e87c6721b1..163a67b97a40 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_NR)
+		return 0;
+
 	if (!data_type_movable(a.data_type) ||
 	    !bch2_bucket_sectors_fragmented(ca, a))
 		return 0;
--