[PATCH 3/3] mtd: rawnand: sunxi: use a stack buffer for BBM randomization

Variable protected user-data lengths replaced the original four-byte
stack buffer with a heap allocation before compensating the bad block
marker. The allocation is unchecked, and a zero length returns
ZERO_SIZE_PTR which sunxi_nfc_randomize_bbm() dereferences.

The controller supports at most 32 protected user-data bytes per ECC
step, so use a zero-initialized buffer of that bounded size. This
removes the allocation failure path and keeps zero-sized invalid layouts
from dereferencing ZERO_SIZE_PTR.

Fixes: 54dcd6aa69db ("mtd: rawnand: sunxi: introduce maximize variable user data length")
Signed-off-by: James Hilliard <[email protected]>
---
 drivers/mtd/nand/raw/sunxi_nand.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/drivers/mtd/nand/raw/sunxi_nand.c b/drivers/mtd/nand/raw/sunxi_nand.c
index 01a0d0fa7b62..83666dd6cb2a 100644
--- a/drivers/mtd/nand/raw/sunxi_nand.c
+++ b/drivers/mtd/nand/raw/sunxi_nand.c
@@ -222,6 +222,7 @@
  * USER_DATA_LEN registers.
  */
 #define USER_DATA_SZ 4
+#define SUNXI_NFC_MAX_USER_DATA_SZ 32
 
 /**
  * struct sunxi_nand_chip_sel - stores information related to NAND Chip Select
@@ -1003,11 +1004,10 @@ static void sunxi_nfc_hw_ecc_set_prot_oob_bytes(struct nand_chip *nand,
 	struct sunxi_nfc *nfc = to_sunxi_nfc(nand->controller);
 	struct sunxi_nand_chip *sunxi_nand = to_sunxi_nand(nand);
 	unsigned int user_data_sz = sunxi_nfc_user_data_sz(sunxi_nand, step);
-	u8 *user_data = NULL;
+	u8 user_data[SUNXI_NFC_MAX_USER_DATA_SZ] = {};
 
 	/* Randomize the Bad Block Marker. */
 	if (bbm && (nand->options & NAND_NEED_SCRAMBLING)) {
-		user_data = kmalloc(user_data_sz, GFP_KERNEL);
 		memcpy(user_data, oob, user_data_sz);
 		sunxi_nfc_randomize_bbm(nand, page, user_data);
 		oob = user_data;
@@ -1040,7 +1040,6 @@ static void sunxi_nfc_hw_ecc_set_prot_oob_bytes(struct nand_chip *nand,
 		}
 	}
 
-	kfree(user_data);
 }
 
 static void sunxi_nfc_hw_ecc_update_stats(struct nand_chip *nand,

-- 
2.53.0