mtd: spi-nor: Check consistency of the memory size extracted from the SFDP

One field of the flash parameter table contains information about the
flash device size.
Most of the time the data extracted from this field is valid, but
sometimes the BFPT section of the SFDP table is corrupted or invalid and
this field is set to 0xffffffff, thus resulting in an integer overflow
when setting params->size.

Since NOR devices are anayway always smaller than 2^64 bytes, we can
easily stop the BFPT parsing if the size reported in this table is
invalid.

Fixes: f384b352 ("mtd: spi-nor: parse Serial Flash Discoverable Parameters (SFDP) tables")
Reported-by: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Boris Brezillon <boris.brezillon@free-electrons.com>
Tested-by: Geert Uytterhoeven <geert+renesas@glider.be>
Acked-by: Cyrille Pitchen <cyrille.pitchen@wedev4u.com>

drivers/mtd/spi-nor/spi-nor.c

@@ -2127,6 +2127,15 @@ static int spi_nor_parse_bfpt(struct spi_nor *nor,
 	params->size = bfpt.dwords[BFPT_DWORD(2)];
 	if (params->size & BIT(31)) {
 		params->size &= ~BIT(31);
+
+		/*
+		 * Prevent overflows on params->size. Anyway, a NOR of 2^64
+		 * bits is unlikely to exist so this error probably means
+		 * the BFPT we are reading is corrupted/wrong.
+		 */
+		if (params->size > 63)
+			return -EINVAL;
+
 		params->size = 1ULL << params->size;
 	} else {
 		params->size++;