mtd: ensure index is positive

The index is signed, make sure it is not negative
when we read the array element.
Signed-off-by: NRoel Kluin <roel.kluin@gmail.com>
Signed-off-by: NArtem Bityutskiy <Artem.Bityutskiy@nokia.com>
Signed-off-by: NDavid Woodhouse <David.Woodhouse@intel.com>

drivers/mtd/mtdcore.c

@@ -447,7 +447,7 @@ struct mtd_info *get_mtd_device(struct mtd_info *mtd, int num)
 		for (i=0; i< MAX_MTD_DEVICES; i++)
 			if (mtd_table[i] == mtd)
 				ret = mtd_table[i];
-	} else if (num < MAX_MTD_DEVICES) {
+	} else if (num >= 0 && num < MAX_MTD_DEVICES) {
 		ret = mtd_table[num];
 		if (mtd && mtd != ret)
 			ret = NULL;

drivers/mtd/nand/fsl_upm.c

@@ -112,7 +112,7 @@ static void fun_select_chip(struct mtd_info *mtd, int mchip_nr)
 
 	if (mchip_nr == -1) {
 		chip->cmd_ctrl(mtd, NAND_CMD_NONE, 0 | NAND_CTRL_CHANGE);
-	} else if (mchip_nr >= 0) {
+	} else if (mchip_nr >= 0 && mchip_nr < NAND_MAX_CHIPS) {
 		fun->mchip_number = mchip_nr;
 		chip->IO_ADDR_R = fun->io_base + fun->mchip_offsets[mchip_nr];
 		chip->IO_ADDR_W = chip->IO_ADDR_R;