mtd: rawnand: qcom: fix memory corruption that causes panic

This patch fixes a memory corruption that occurred in the
qcom-nandc driver since it was converted to nand_scan().

On boot, an affected device will panic from a NPE at a weird place:
| Unable to handle kernel NULL pointer dereference at virtual address 0
| pgd = (ptrval)
| [00000000] *pgd=00000000
| Internal error: Oops: 80000005 [#1] SMP ARM
| CPU: 0 PID: 1 Comm: swapper/0 Not tainted 4.19.9 #0
| Hardware name: Generic DT based system
| PC is at   (null)
| LR is at nand_block_isbad+0x90/0xa4
| pc : [<00000000>]    lr : [<c0592240>]    psr: 80000013
| sp : cf839d40  ip : 00000000  fp : cfae9e20
| r10: cf815810  r9 : 00000000  r8 : 00000000
| r7 : 00000000  r6 : 00000000  r5 : 00000001  r4 : cf815810
| r3 : 00000000  r2 : cfae9810  r1 : ffffffff  r0 : cf815810
| Flags: Nzcv  IRQs on  FIQs on  Mode SVC_32  ISA ARM  Segment none
| Control: 10c5387d  Table: 8020406a  DAC: 00000051
| Process swapper/0 (pid: 1, stack limit = 0x(ptrval))
| [<c0592240>] (nand_block_isbad) from [<c0580a94>]
| [<c0580a94>] (allocate_partition) from [<c05811e4>]
| [<c05811e4>] (add_mtd_partitions) from [<c0581164>]
| [<c0581164>] (parse_mtd_partitions) from [<c057def4>]
| [<c057def4>] (mtd_device_parse_register) from [<c059d274>]
| [<c059d274>] (qcom_nandc_probe) from [<c0567f00>]

The problem is that the nand_scan()'s qcom_nand_attach_chip callback
is updating the nandc->max_cwperpage from 1 to 4. This causes the
sg_init_table of clear_bam_transaction() in the driver's
qcom_nandc_block_bad() to memset much more than what was initially
allocated by alloc_bam_transaction().

This patch restores the old behavior by reallocating the shared bam
transaction alloc_bam_transaction() after the chip was identified,
but before mtd_device_parse_register() (which is an alias for
mtd_device_register() - see panic) gets called. This fixes the
corruption and the driver is working again.

Cc: stable@vger.kernel.org
Fixes: 6a3cec64 ("mtd: rawnand: qcom: convert driver to nand_scan()")
Signed-off-by: Christian Lamparter <chunkeey@gmail.com>
Acked-by: Miquel Raynal <miquel.raynal@bootlin.com>
Signed-off-by: Boris Brezillon <bbrezillon@kernel.org>

drivers/mtd/nand/raw/qcom_nandc.c

@@ -2833,6 +2833,16 @@ static int qcom_nand_host_init_and_register(struct qcom_nand_controller *nandc,
 	if (ret)
 		return ret;
 
+	if (nandc->props->is_bam) {
+		free_bam_transaction(nandc);
+		nandc->bam_txn = alloc_bam_transaction(nandc);
+		if (!nandc->bam_txn) {
+			dev_err(nandc->dev,
+				"failed to allocate bam transaction\n");
+			return -ENOMEM;
+		}
+	}
+
 	ret = mtd_device_register(mtd, NULL, 0);
 	if (ret)
 		nand_cleanup(chip);
@@ -2847,16 +2857,6 @@ static int qcom_probe_nand_devices(struct qcom_nand_controller *nandc)
 	struct qcom_nand_host *host;
 	int ret;
 
-	if (nandc->props->is_bam) {
-		free_bam_transaction(nandc);
-		nandc->bam_txn = alloc_bam_transaction(nandc);
-		if (!nandc->bam_txn) {
-			dev_err(nandc->dev,
-				"failed to allocate bam transaction\n");
-			return -ENOMEM;
-		}
-	}
-
 	for_each_available_child_of_node(dn, child) {
 		host = devm_kzalloc(dev, sizeof(*host), GFP_KERNEL);
 		if (!host) {