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