linux-kernel - [PATCH] mtdchar: fix integer overflow in read/write ioctls

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Message-ID: <020f98d2-eee1-434e-8236-775cca9fd157@stanley.mountain>
Date: Fri, 6 Dec 2024 23:26:36 +0300
From: Dan Carpenter <dan.carpenter@...aro.org>
To: Michał Kępień <kernel@...pniu.pl>
Cc: Miquel Raynal <miquel.raynal@...tlin.com>,
	Richard Weinberger <richard@....at>,
	Vignesh Raghavendra <vigneshr@...com>,
	linux-mtd@...ts.infradead.org, linux-kernel@...r.kernel.org,
	kernel-janitors@...r.kernel.org
Subject: [PATCH] mtdchar: fix integer overflow in read/write ioctls

The "req.start" and "req.len" variables are u64 values that come from the
user at the start of the function.  We mask away the high 32 bits of
"req.len" so that's capped at U32_MAX but the "req.start" variable can go
up to U64_MAX.

Use check_add_overflow() to fix this bug.

Fixes: 6420ac0af95d ("mtdchar: prevent unbounded allocation in MEMWRITE ioctl")
Signed-off-by: Dan Carpenter <dan.carpenter@...aro.org>
---
 drivers/mtd/mtdchar.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/mtd/mtdchar.c b/drivers/mtd/mtdchar.c
index 8dc4f5c493fc..335c702633ff 100644
--- a/drivers/mtd/mtdchar.c
+++ b/drivers/mtd/mtdchar.c
@@ -599,6 +599,7 @@ mtdchar_write_ioctl(struct mtd_info *mtd, struct mtd_write_req __user *argp)
 	uint8_t *datbuf = NULL, *oobbuf = NULL;
 	size_t datbuf_len, oobbuf_len;
 	int ret = 0;
+	u64 end;
 
 	if (copy_from_user(&req, argp, sizeof(req)))
 		return -EFAULT;
@@ -618,7 +619,7 @@ mtdchar_write_ioctl(struct mtd_info *mtd, struct mtd_write_req __user *argp)
 	req.len &= 0xffffffff;
 	req.ooblen &= 0xffffffff;
 
-	if (req.start + req.len > mtd->size)
+	if (check_add_overflow(req.start, req.len, &end) || end > mtd->size)
 		return -EINVAL;
 
 	datbuf_len = min_t(size_t, req.len, mtd->erasesize);
@@ -698,6 +699,7 @@ mtdchar_read_ioctl(struct mtd_info *mtd, struct mtd_read_req __user *argp)
 	size_t datbuf_len, oobbuf_len;
 	size_t orig_len, orig_ooblen;
 	int ret = 0;
+	u64 end;
 
 	if (copy_from_user(&req, argp, sizeof(req)))
 		return -EFAULT;
@@ -724,7 +726,7 @@ mtdchar_read_ioctl(struct mtd_info *mtd, struct mtd_read_req __user *argp)
 	req.len &= 0xffffffff;
 	req.ooblen &= 0xffffffff;
 
-	if (req.start + req.len > mtd->size) {
+	if (check_add_overflow(req.start, req.len, &end) || end > mtd->size) {
 		ret = -EINVAL;
 		goto out;
 	}
-- 
2.45.2