[PATCH 3.16 075/366] iio:kfifo_buf: check for uint overflow

[Ben Hutchings]

3.16.60-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Martin Kelly <mkelly@xxxxxxxx>

commit 3d13de4b027d5f6276c0f9d3a264f518747d83f2 upstream.

Currently, the following causes a kernel OOPS in memcpy:

echo 1073741825 > buffer/length
echo 1 > buffer/enable

Note that using 1073741824 instead of 1073741825 causes "write error:
Cannot allocate memory" but no OOPS.

This is because 1073741824 == 2^30 and 1073741825 == 2^30+1. Since kfifo
rounds up to the nearest power of 2, it will actually call kmalloc with
roundup_pow_of_two(length) * bytes_per_datum.

Using length == 1073741825 and bytes_per_datum == 2, we get:

kmalloc(roundup_pow_of_two(1073741825) * 2
or kmalloc(2147483648 * 2)
or kmalloc(4294967296)
or kmalloc(UINT_MAX + 1)

so this overflows to 0, causing kmalloc to return ZERO_SIZE_PTR and
subsequent memcpy to fail once the device is enabled.

Fix this by checking for overflow prior to allocating a kfifo. With this
check added, the above code returns -EINVAL when enabling the buffer,
rather than causing an OOPS.

Signed-off-by: Martin Kelly <mkelly@xxxxxxxx>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@xxxxxxxxxx>
[bwh: Backported to 3.16: adjust filename]
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
 drivers/iio/kfifo_buf.c | 7 +++++++
 1 file changed, 7 insertions(+)

--- a/drivers/iio/kfifo_buf.c
+++ b/drivers/iio/kfifo_buf.c
@@ -24,6 +24,13 @@ static inline int __iio_allocate_kfifo(s
 	if ((length == 0) || (bytes_per_datum == 0))
 		return -EINVAL;
 
+	/*
+	 * Make sure we don't overflow an unsigned int after kfifo rounds up to
+	 * the next power of 2.
+	 */
+	if (roundup_pow_of_two(length) > UINT_MAX / bytes_per_datum)
+		return -EINVAL;
+
 	return __kfifo_alloc((struct __kfifo *)&buf->kf, length,
 			     bytes_per_datum, GFP_KERNEL);
 }