nvmem: eeprom: at25: fix FRAM byte_len

Commit fd307a4 ("nvmem: prepare basics for FRAM support") added
support for FRAM devices such as the Cypress FM25V. During testing, it
was found that the FRAM detects properly, however reads and writes fail.
Upon further investigation, two problem were found in at25_probe() routine.

1) In the case of an FRAM device without platform data, eg.
       fram == true && spi->dev.platform_data == NULL
the stack local variable "struct spi_eeprom chip" is not initialized
fully, prior to being copied into at25->chip. The chip.flags field in
particular can cause problems.

2) The byte_len of FRAM is computed from its ID register, and is stored
into the stack local "struct spi_eeprom chip" structure. This happens
after the same structure has been copied into at25->chip. As a result,
at25->chip.byte_len does not contain the correct length of the device.
In turn this can cause checks at beginning of at25_ee_read() to fail
(or equally, it could allow reads beyond the end of the device length).

Fix both of these issues by eliminating the on-stack struct spi_eeprom.
Instead use the one inside at25_data structure, which starts of zeroed.

Fixes: fd307a4 ("nvmem: prepare basics for FRAM support")
Cc: stable <stable@vger.kernel.org>
Reviewed-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Ralph Siemsen <ralph.siemsen@linaro.org>
Link: https://lore.kernel.org/r/20211108181627.645638-1-ralph.siemsen@linaro.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/misc/eeprom/at25.c

@@ -376,7 +376,6 @@ MODULE_DEVICE_TABLE(spi, at25_spi_ids);
 static int at25_probe(struct spi_device *spi)
 {
 	struct at25_data	*at25 = NULL;
-	struct spi_eeprom	chip;
 	int			err;
 	int			sr;
 	u8 id[FM25_ID_LEN];
@@ -389,15 +388,18 @@ static int at25_probe(struct spi_device *spi)
 	if (match && !strcmp(match->compatible, "cypress,fm25"))
 		is_fram = 1;
 
+	at25 = devm_kzalloc(&spi->dev, sizeof(struct at25_data), GFP_KERNEL);
+	if (!at25)
+		return -ENOMEM;
+
 	/* Chip description */
-	if (!spi->dev.platform_data) {
-		if (!is_fram) {
-			err = at25_fw_to_chip(&spi->dev, &chip);
-			if (err)
-				return err;
-		}
-	} else
-		chip = *(struct spi_eeprom *)spi->dev.platform_data;
+	if (spi->dev.platform_data) {
+		memcpy(&at25->chip, spi->dev.platform_data, sizeof(at25->chip));
+	} else if (!is_fram) {
+		err = at25_fw_to_chip(&spi->dev, &at25->chip);
+		if (err)
+			return err;
+	}
 
 	/* Ping the chip ... the status register is pretty portable,
 	 * unlike probing manufacturer IDs.  We do expect that system
@@ -409,12 +411,7 @@ static int at25_probe(struct spi_device *spi)
 		return -ENXIO;
 	}
 
-	at25 = devm_kzalloc(&spi->dev, sizeof(struct at25_data), GFP_KERNEL);
-	if (!at25)
-		return -ENOMEM;
-
 	mutex_init(&at25->lock);
-	at25->chip = chip;
 	at25->spi = spi;
 	spi_set_drvdata(spi, at25);
 
@@ -431,7 +428,7 @@ static int at25_probe(struct spi_device *spi)
 			dev_err(&spi->dev, "Error: unsupported size (id %02x)\n", id[7]);
 			return -ENODEV;
 		}
-		chip.byte_len = int_pow(2, id[7] - 0x21 + 4) * 1024;
+		at25->chip.byte_len = int_pow(2, id[7] - 0x21 + 4) * 1024;
 
 		if (at25->chip.byte_len > 64 * 1024)
 			at25->chip.flags |= EE_ADDR3;
@@ -464,7 +461,7 @@ static int at25_probe(struct spi_device *spi)
 	at25->nvmem_config.type = is_fram ? NVMEM_TYPE_FRAM : NVMEM_TYPE_EEPROM;
 	at25->nvmem_config.name = dev_name(&spi->dev);
 	at25->nvmem_config.dev = &spi->dev;
-	at25->nvmem_config.read_only = chip.flags & EE_READONLY;
+	at25->nvmem_config.read_only = at25->chip.flags & EE_READONLY;
 	at25->nvmem_config.root_only = true;
 	at25->nvmem_config.owner = THIS_MODULE;
 	at25->nvmem_config.compat = true;
@@ -474,17 +471,18 @@ static int at25_probe(struct spi_device *spi)
 	at25->nvmem_config.priv = at25;
 	at25->nvmem_config.stride = 1;
 	at25->nvmem_config.word_size = 1;
-	at25->nvmem_config.size = chip.byte_len;
+	at25->nvmem_config.size = at25->chip.byte_len;
 
 	at25->nvmem = devm_nvmem_register(&spi->dev, &at25->nvmem_config);
 	if (IS_ERR(at25->nvmem))
 		return PTR_ERR(at25->nvmem);
 
 	dev_info(&spi->dev, "%d %s %s %s%s, pagesize %u\n",
-		 (chip.byte_len < 1024) ? chip.byte_len : (chip.byte_len / 1024),
-		 (chip.byte_len < 1024) ? "Byte" : "KByte",
+		 (at25->chip.byte_len < 1024) ?
+			at25->chip.byte_len : (at25->chip.byte_len / 1024),
+		 (at25->chip.byte_len < 1024) ? "Byte" : "KByte",
 		 at25->chip.name, is_fram ? "fram" : "eeprom",
-		 (chip.flags & EE_READONLY) ? " (readonly)" : "",
+		 (at25->chip.flags & EE_READONLY) ? " (readonly)" : "",
 		 at25->chip.page_size);
 	return 0;
 }