KVM: Harden copying of userspace-array against overflow

kvm_main.c utilizes vmemdup_user() and array_size() to copy a userspace
array. Currently, this does not check for an overflow.

Use the new wrapper vmemdup_array_user() to copy the array more safely.

Note, KVM explicitly checks the number of entries before duplicating the
array, i.e. adding the overflow check should be a glorified nop.

Suggested-by: Dave Airlie <airlied@redhat.com>
Signed-off-by: Philipp Stanner <pstanner@redhat.com>
Link: https://lore.kernel.org/r/20231102181526.43279-4-pstanner@redhat.com
[sean: call out that KVM pre-checks the number of entries]
Signed-off-by: Sean Christopherson <seanjc@google.com>

Author: Philipp Stanner

virt/kvm/kvm_main.c

@@ -5262,9 +5262,8 @@ static long kvm_vm_ioctl(struct file *filp,
 			goto out;
 		if (routing.nr) {
 			urouting = argp;
-			entries = vmemdup_user(urouting->entries,
-					       array_size(sizeof(*entries),
-							  routing.nr));
+			entries = vmemdup_array_user(urouting->entries,
+						     routing.nr, sizeof(*entries));
 			if (IS_ERR(entries)) {
 				r = PTR_ERR(entries);
 				goto out;