nvmem: rave-sp-eeprom: Remove VLA usage

In the quest to remove all stack VLA usage from the kernel[1], this
uses the maximum allocation size for the stack and adds a sanity check,
similar to what has already be done for the regular rave-sp driver.

[1] https://lkml.kernel.org/r/CA+55aFzCG-zNmZwX4A2FQpadafLfEzK6CC=qPXydAacU1RqZWA@mail.gmail.com

Signed-off-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Andrey Smirnov <andrew.smirnov@gmail.com>
Tested-by: Andrey Smirnov <andrew.smirnov@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/nvmem/rave-sp-eeprom.c

@@ -35,6 +35,7 @@ enum rave_sp_eeprom_header_size {
 	RAVE_SP_EEPROM_HEADER_SMALL = 4U,
 	RAVE_SP_EEPROM_HEADER_BIG   = 5U,
 };
+#define RAVE_SP_EEPROM_HEADER_MAX	RAVE_SP_EEPROM_HEADER_BIG
 
 #define	RAVE_SP_EEPROM_PAGE_SIZE	32U
 
@@ -97,9 +98,12 @@ static int rave_sp_eeprom_io(struct rave_sp_eeprom *eeprom,
 	const unsigned int rsp_size =
 		is_write ? sizeof(*page) - sizeof(page->data) : sizeof(*page);
 	unsigned int offset = 0;
-	u8 cmd[cmd_size];
+	u8 cmd[RAVE_SP_EEPROM_HEADER_MAX + sizeof(page->data)];
 	int ret;
 
+	if (WARN_ON(cmd_size > sizeof(cmd)))
+		return -EINVAL;
+
 	cmd[offset++] = eeprom->address;
 	cmd[offset++] = 0;
 	cmd[offset++] = type;