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

This patch fixes a memory corruption that occurred in the
nand_scan() path for Hynix nand device.

On boot, for Hynix nand device will panic at a weird place:
| Unable to handle kernel NULL pointer dereference at virtual
  address 00000070
| [00000070] *pgd=00000000
| Internal error: Oops: 5 [#1] PREEMPT SMP ARM
| Modules linked in:
| CPU: 0 PID: 1 Comm: swapper/0 Not tainted 5.17.0-01473-g13ae1769cfb0
  #38
| Hardware name: Generic DT based system
| PC is at nandc_set_reg+0x8/0x1c
| LR is at qcom_nandc_command+0x20c/0x5d0
| pc : [<c088b74c>]    lr : [<c088d9c8>]    psr: 00000113
| sp : c14adc50  ip : c14ee208  fp : c0cc970c
| r10: 000000a3  r9 : 00000000  r8 : 00000040
| r7 : c16f6a00  r6 : 00000090  r5 : 00000004  r4 :c14ee040
| r3 : 00000000  r2 : 0000000b  r1 : 00000000  r0 :c14ee040
| Flags: nzcv  IRQs on  FIQs on  Mode SVC_32  ISA ARM Segment none
| Control: 10c5387d  Table: 8020406a  DAC: 00000051
| Register r0 information: slab kmalloc-2k start c14ee000 pointer offset
  64 size 2048
| Process swapper/0 (pid: 1, stack limit = 0x(ptrval))
| nandc_set_reg from qcom_nandc_command+0x20c/0x5d0
| qcom_nandc_command from nand_readid_op+0x198/0x1e8
| nand_readid_op from hynix_nand_has_valid_jedecid+0x30/0x78
| hynix_nand_has_valid_jedecid from hynix_nand_init+0xb8/0x454
| hynix_nand_init from nand_scan_with_ids+0xa30/0x14a8
| nand_scan_with_ids from qcom_nandc_probe+0x648/0x7b0
| qcom_nandc_probe from platform_probe+0x58/0xac

The problem is that the nand_scan()'s qcom_nand_attach_chip callback
is updating the nandc->max_cwperpage from 1 to 4 or 8 based on page size.
This causes the sg_init_table of clear_bam_transaction() in the driver's
qcom_nandc_command() to memset much more than what was initially
allocated by alloc_bam_transaction().

This patch will update nandc->max_cwperpage 1 to 4 or 8 based on page
size in qcom_nand_attach_chip call back after freeing the previously
allocated memory for bam txn as per nandc->max_cwperpage = 1 and then
again allocating bam txn as per nandc->max_cwperpage = 4 or 8 based on
page size in qcom_nand_attach_chip call back itself.

Cc: stable@vger.kernel.org
Fixes: 6a3cec64 ("mtd: rawnand: qcom: convert driver to nand_scan()")
Reported-by: Konrad Dybcio <konrad.dybcio@somainline.org>
Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Co-developed-by: Sricharan R <quic_srichara@quicinc.com>
Signed-off-by: Sricharan R <quic_srichara@quicinc.com>
Signed-off-by: Md Sadre Alam <quic_mdalam@quicinc.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/1650268107-5363-1-git-send-email-quic_mdalam@quicinc.com

drivers/mtd/nand/raw/qcom_nandc.c

@@ -2651,10 +2651,23 @@ static int qcom_nand_attach_chip(struct nand_chip *chip)
 	ecc->engine_type = NAND_ECC_ENGINE_TYPE_ON_HOST;
 
 	mtd_set_ooblayout(mtd, &qcom_nand_ooblayout_ops);
+	/* Free the initially allocated BAM transaction for reading the ONFI params */
+	if (nandc->props->is_bam)
+		free_bam_transaction(nandc);
 
 	nandc->max_cwperpage = max_t(unsigned int, nandc->max_cwperpage,
 				     cwperpage);
 
+	/* Now allocate the BAM transaction based on updated max_cwperpage */
+	if (nandc->props->is_bam) {
+		nandc->bam_txn = alloc_bam_transaction(nandc);
+		if (!nandc->bam_txn) {
+			dev_err(nandc->dev,
+				"failed to allocate bam transaction\n");
+			return -ENOMEM;
+		}
+	}
+
 	/*
 	 * DATA_UD_BYTES varies based on whether the read/write command protects
 	 * spare data with ECC too. We protect spare data by default, so we set
@@ -2955,17 +2968,6 @@ 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");
-			nand_cleanup(chip);
-			return -ENOMEM;
-		}
-	}
-
 	ret = mtd_device_parse_register(mtd, probes, NULL, NULL, 0);
 	if (ret)
 		nand_cleanup(chip);