KVM: kill file->f_count abuse in kvm

Use kvm own refcounting instead of playing with ->filp->f_count.
That will allow to get rid of a lot of crap in anon_inode_getfd() and
kill a race in kvm_dev_ioctl_create_vm() (file might have been closed
immediately by another thread, so ->filp might point to already freed
struct file when we get around to setting it).

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Avi Kivity <avi@qumranet.com>

2 files changed, 6 insertions, 7 deletions

diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 4e16682ee8bb..398978972b7a 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -110,7 +110,6 @@ struct kvm {
                                         KVM_PRIVATE_MEM_SLOTS];
         struct kvm_vcpu *vcpus[KVM_MAX_VCPUS];
         struct list_head vm_list;
-        struct file *filp;
         struct kvm_io_bus mmio_bus;
         struct kvm_io_bus pio_bus;
         struct kvm_vm_stat stat;
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index d3cb4cc0a5aa..c82cf15730a1 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -818,7 +818,7 @@ static int kvm_vcpu_release(struct inode *inode, struct file *filp)
 {
         struct kvm_vcpu *vcpu = filp->private_data;
 
-        fput(vcpu->kvm->filp);
+        kvm_put_kvm(vcpu->kvm);
         return 0;
 }
 
@@ -840,9 +840,10 @@ static int create_vcpu_fd(struct kvm_vcpu *vcpu)
 
         r = anon_inode_getfd(&fd, &inode, &file,
                              "kvm-vcpu", &kvm_vcpu_fops, vcpu);
-        if (r)
+        if (r) {
+                kvm_put_kvm(vcpu->kvm);
                 return r;
-        atomic_inc(&vcpu->kvm->filp->f_count);
+        }
         return fd;
 }
 
@@ -877,6 +878,7 @@ static int kvm_vm_ioctl_create_vcpu(struct kvm *kvm, int n)
         mutex_unlock(&kvm->lock);
 
         /* Now it's all set up, let userspace reach it */
+        kvm_get_kvm(kvm);
         r = create_vcpu_fd(vcpu);
         if (r < 0)
                 goto unlink;
@@ -1176,12 +1178,10 @@ static int kvm_dev_ioctl_create_vm(void)
                 return PTR_ERR(kvm);
         r = anon_inode_getfd(&fd, &inode, &file, "kvm-vm", &kvm_vm_fops, kvm);
         if (r) {
-                kvm_destroy_vm(kvm);
+                kvm_put_kvm(kvm);
                 return r;
         }
 
-        kvm->filp = file;
-
         return fd;
 }