From a1eda864c04cf24ea1130334963c6199318f6f95 Mon Sep 17 00:00:00 2001 From: Michał Kępień Date: Mon, 16 May 2022 09:06:00 +0200 Subject: mtdchar: prevent integer overflow in a safety check MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Commit 6420ac0af95d ("mtdchar: prevent unbounded allocation in MEMWRITE ioctl") added a safety check to mtdchar_write_ioctl() which attempts to ensure that the write request sent by user space does not extend beyond the MTD device's size. However, that check contains an addition of two struct mtd_write_req fields, 'start' and 'len', both of which are u64 variables. The result of that addition can overflow, allowing the safety check to be bypassed. The arguably simplest fix - changing the data types of the relevant struct mtd_write_req fields - is not feasible as it would break user space. Fix by making mtdchar_write_ioctl() truncate the value provided by user space in the 'len' field of struct mtd_write_req, so that only the lower 32 bits of that field are used, preventing the overflow. While the 'ooblen' field of struct mtd_write_req is not currently used in any similarly flawed safety check, also truncate it to 32 bits, for consistency with the 'len' field and with other MTD routines handling OOB data. Update include/uapi/mtd/mtd-abi.h accordingly. Suggested-by: Richard Weinberger Signed-off-by: Michał Kępień Signed-off-by: Miquel Raynal Link: https://lore.kernel.org/linux-mtd/20220516070601.11428-2-kernel@kempniu.pl --- drivers/mtd/mtdchar.c | 3 +++ 1 file changed, 3 insertions(+) (limited to 'drivers/mtd/mtdchar.c') diff --git a/drivers/mtd/mtdchar.c b/drivers/mtd/mtdchar.c index d0f9c4b0285c..b2700f8467ff 100644 --- a/drivers/mtd/mtdchar.c +++ b/drivers/mtd/mtdchar.c @@ -615,6 +615,9 @@ static int mtdchar_write_ioctl(struct mtd_info *mtd, if (!usr_oob) req.ooblen = 0; + req.len &= 0xffffffff; + req.ooblen &= 0xffffffff; + if (req.start + req.len > mtd->size) return -EINVAL; -- cgit v1.2.3