From: Elena Reshetova <elena.reshetova@intel.com>
Date: Mon, 20 Feb 2017 11:06:21 +0000 (+0200)
Subject: kvm: convert kvm.users_count from atomic_t to refcount_t
X-Git-Url: https://git.stricted.de/?a=commitdiff_plain;h=e3736c3eb3a6f7c0966923b629c9f92b558aa9c7;p=GitHub%2Fmoto-9609%2Fandroid_kernel_motorola_exynos9610.git

kvm: convert kvm.users_count from atomic_t to refcount_t

refcount_t type and corresponding API should be
used instead of atomic_t when the variable is used as
a reference counter. This allows to avoid accidental
refcounter overflows that might lead to use-after-free
situations.

Signed-off-by: Elena Reshetova <elena.reshetova@intel.com>
Signed-off-by: Hans Liljestrand <ishkamiel@gmail.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: David Windsor <dwindsor@gmail.com>
Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>
---

diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 8d69d5150748..2c14ad9809da 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -26,6 +26,7 @@
 #include <linux/context_tracking.h>
 #include <linux/irqbypass.h>
 #include <linux/swait.h>
+#include <linux/refcount.h>
 #include <asm/signal.h>
 
 #include <linux/kvm.h>
@@ -401,7 +402,7 @@ struct kvm {
 #endif
 	struct kvm_vm_stat stat;
 	struct kvm_arch arch;
-	atomic_t users_count;
+	refcount_t users_count;
 #ifdef KVM_COALESCED_MMIO_PAGE_OFFSET
 	struct kvm_coalesced_mmio_ring *coalesced_mmio_ring;
 	spinlock_t ring_lock;
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index cc4d6e0dd2a2..c6b7aff634be 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -617,7 +617,7 @@ static struct kvm *kvm_create_vm(unsigned long type)
 	mutex_init(&kvm->lock);
 	mutex_init(&kvm->irq_lock);
 	mutex_init(&kvm->slots_lock);
-	atomic_set(&kvm->users_count, 1);
+	refcount_set(&kvm->users_count, 1);
 	INIT_LIST_HEAD(&kvm->devices);
 
 	r = kvm_arch_init_vm(kvm, type);
@@ -747,13 +747,13 @@ static void kvm_destroy_vm(struct kvm *kvm)
 
 void kvm_get_kvm(struct kvm *kvm)
 {
-	atomic_inc(&kvm->users_count);
+	refcount_inc(&kvm->users_count);
 }
 EXPORT_SYMBOL_GPL(kvm_get_kvm);
 
 void kvm_put_kvm(struct kvm *kvm)
 {
-	if (atomic_dec_and_test(&kvm->users_count))
+	if (refcount_dec_and_test(&kvm->users_count))
 		kvm_destroy_vm(kvm);
 }
 EXPORT_SYMBOL_GPL(kvm_put_kvm);
@@ -3639,7 +3639,7 @@ static int kvm_debugfs_open(struct inode *inode, struct file *file,
 	 * To avoid the race between open and the removal of the debugfs
 	 * directory we test against the users count.
 	 */
-	if (!atomic_add_unless(&stat_data->kvm->users_count, 1, 0))
+	if (!refcount_inc_not_zero(&stat_data->kvm->users_count))
 		return -ENOENT;
 
 	if (simple_attr_open(inode, file, get, set, fmt)) {