kvm: use anon_inode_getfd() with O_CLOEXEC flag

KVM uses anon_inode_get() to allocate file descriptors as part
of some of its ioctls. But those ioctls are lacking a flag argument
allowing userspace to choose options for the newly opened file descriptor.

In such case it's advised to use O_CLOEXEC by default so that
userspace is allowed to choose, without race, if the file descriptor
is going to be inherited across exec().

This patch set O_CLOEXEC flag on all file descriptors created
with anon_inode_getfd() to not leak file descriptors across exec().

Signed-off-by: Yann Droneaud <ydroneaud@opteya.com>
Link: http://lkml.kernel.org/r/cover.1377372576.git.ydroneaud@opteya.com
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Gleb Natapov <gleb@redhat.com>

virt/kvm/kvm_main.c

@@ -1896,7 +1896,7 @@ static struct file_operations kvm_vcpu_fops = {
  */
 static int create_vcpu_fd(struct kvm_vcpu *vcpu)
 {
-	return anon_inode_getfd("kvm-vcpu", &kvm_vcpu_fops, vcpu, O_RDWR);
+	return anon_inode_getfd("kvm-vcpu", &kvm_vcpu_fops, vcpu, O_RDWR | O_CLOEXEC);
 }
 
 /*
@@ -2305,7 +2305,7 @@ static int kvm_ioctl_create_device(struct kvm *kvm,
 		return ret;
 	}
 
-	ret = anon_inode_getfd(ops->name, &kvm_device_fops, dev, O_RDWR);
+	ret = anon_inode_getfd(ops->name, &kvm_device_fops, dev, O_RDWR | O_CLOEXEC);
 	if (ret < 0) {
 		ops->destroy(dev);
 		return ret;
@@ -2589,7 +2589,7 @@ static int kvm_dev_ioctl_create_vm(unsigned long type)
 		return r;
 	}
 #endif
-	r = anon_inode_getfd("kvm-vm", &kvm_vm_fops, kvm, O_RDWR);
+	r = anon_inode_getfd("kvm-vm", &kvm_vm_fops, kvm, O_RDWR | O_CLOEXEC);
 	if (r < 0)
 		kvm_put_kvm(kvm);