[PATCH 5.16 168/227] mtd: phram: Prevent divide by zero bug in phram_setup()

Greg Kroah-Hartman
2022-02-21T10:03:04Z

From: Dan Carpenter <dan.carpenter@oracle.com>

commit 3e3765875b1b8864898603768fd5c93eeb552211 upstream.

The problem is that "erasesize" is a uint64_t type so it might be
non-zero but the lower 32 bits are zero so when it's truncated,
"(uint32_t)erasesize", then that value is zero. This leads to a
divide by zero bug.

Avoid the bug by delaying the divide until after we have validated
that "erasesize" is non-zero and within the uint32_t range.

Fixes: dc2b3e5cbc80 ("mtd: phram: use div_u64_rem to stop overwrite len in phram_setup")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20220121115505.GI1978@kadam
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/mtd/devices/phram.c | 12 ++++++++----
1 file changed, 8 insertions(+), 4 deletions(-)

--- a/drivers/mtd/devices/phram.c
+++ b/drivers/mtd/devices/phram.c
@@ -264,15 +264,19 @@ static int phram_setup(const char *val)
}
}

- if (erasesize)
- div_u64_rem(len, (uint32_t)erasesize, &rem);
-
if (len == 0 || erasesize == 0 || erasesize > len
- || erasesize > UINT_MAX || rem) {
+ || erasesize > UINT_MAX) {
parse_err("illegal erasesize or len\n");
ret = -EINVAL;
goto error;
}
+
+ div_u64_rem(len, (uint32_t)erasesize, &rem);
+ if (rem) {
+ parse_err("len is not multiple of erasesize\n");
+ ret = -EINVAL;
+ goto error;
+ }

ret = register_device(name, start, len, (uint32_t)erasesize);
if (ret)