mtd: sharpslpart: fix overflow on block_adr calculation

Multiplying block_num and mtd->erasesize may potentially overflow
as they are both unsigned ints and so the multiplication is evaluated
in unsigned int arithmetic.  Cast block_adr to off_t to ensure
multiplication is off_t sized to avoid any potential overflow.

Detected by CoverityScan, CID#1461264 ("Unintentional integer overflow")
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Acked-by: Andrea Adami <andrea.adami@gmail.com>
Signed-off-by: Boris Brezillon <boris.brezillon@free-electrons.com>

drivers/mtd/parsers/sharpslpart.c

@@ -192,7 +192,7 @@ static int sharpsl_nand_init_ftl(struct mtd_info *mtd, struct sharpsl_ftl *ftl)
 
 	/* create physical-logical table */
 	for (block_num = 0; block_num < phymax; block_num++) {
-		block_adr = block_num * mtd->erasesize;
+		block_adr = (loff_t)block_num * mtd->erasesize;
 
 		if (mtd_block_isbad(mtd, block_adr))
 			continue;
@@ -244,7 +244,7 @@ static int sharpsl_nand_read_laddr(struct mtd_info *mtd,
 		return -EINVAL;
 
 	block_num = ftl->log2phy[log_num];
-	block_adr = block_num * mtd->erasesize;
+	block_adr = (loff_t)block_num * mtd->erasesize;
 	block_ofs = mtd_mod_by_eb((u32)from, mtd);
 
 	err = mtd_read(mtd, block_adr + block_ofs, len, &retlen, buf);