[patch 1/3] xen/privcmd: check for integer overflow in ioctl

[Dan Carpenter <dan.carpenter@oracle.com>]

If m.num is too large then the "m.num * sizeof(*m.arr)" multiplication
could overflow and the access_ok() check wouldn't test the right size.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
---
Only needed in linux-next.

diff --git a/drivers/xen/privcmd.c b/drivers/xen/privcmd.c
index 215a3c0..fdff8f9 100644
--- a/drivers/xen/privcmd.c
+++ b/drivers/xen/privcmd.c
@@ -325,6 +325,8 @@ static long privcmd_ioctl_mmap_batch(void __user *udata, int version)
 			return -EFAULT;
 		/* Returns per-frame error in m.arr. */
 		m.err = NULL;
+		if (m.num > SIZE_MAX / sizeof(*m.arr))
+			return -EINVAL;
 		if (!access_ok(VERIFY_WRITE, m.arr, m.num * sizeof(*m.arr)))
 			return -EFAULT;
 		break;
@@ -332,6 +334,8 @@ static long privcmd_ioctl_mmap_batch(void __user *udata, int version)
 		if (copy_from_user(&m, udata, sizeof(struct privcmd_mmapbatch_v2)))
 			return -EFAULT;
 		/* Returns per-frame error code in m.err. */
+		if (m.num > SIZE_MAX / sizeof(*m.err))
+			return -EINVAL;
 		if (!access_ok(VERIFY_WRITE, m.err, m.num * (sizeof(*m.err))))
 			return -EFAULT;
 		break;