From e2d3fcaf939dded3da604a25ebbea9fb954c2280 Mon Sep 17 00:00:00 2001 From: Paolo Bonzini Date: Mon, 4 Nov 2019 13:23:53 +0100 Subject: KVM: fix placement of refcount initialization Reported by syzkaller: ============================= WARNING: suspicious RCU usage ----------------------------- ./include/linux/kvm_host.h:536 suspicious rcu_dereference_check() usage! other info that might help us debug this: rcu_scheduler_active = 2, debug_locks = 1 no locks held by repro_11/12688. stack backtrace: Call Trace: dump_stack+0x7d/0xc5 lockdep_rcu_suspicious+0x123/0x170 kvm_dev_ioctl+0x9a9/0x1260 [kvm] do_vfs_ioctl+0x1a1/0xfb0 ksys_ioctl+0x6d/0x80 __x64_sys_ioctl+0x73/0xb0 do_syscall_64+0x108/0xaa0 entry_SYSCALL_64_after_hwframe+0x49/0xbe Commit a97b0e773e4 (kvm: call kvm_arch_destroy_vm if vm creation fails) sets users_count to 1 before kvm_arch_init_vm(), however, if kvm_arch_init_vm() fails, we need to decrease this count. By moving it earlier, we can push the decrease to out_err_no_arch_destroy_vm without introducing yet another error label. syzkaller source: https://syzkaller.appspot.com/x/repro.c?x=15209b84e00000 Reported-by: syzbot+75475908cd0910f141ee@syzkaller.appspotmail.com Fixes: a97b0e773e49 ("kvm: call kvm_arch_destroy_vm if vm creation fails") Cc: Jim Mattson Analyzed-by: Wanpeng Li Signed-off-by: Paolo Bonzini --- virt/kvm/kvm_main.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) (limited to 'virt/kvm/kvm_main.c') diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c index e22ff63e5b1a..e7a07132cd7f 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -650,6 +650,7 @@ static struct kvm *kvm_create_vm(unsigned long type) if (init_srcu_struct(&kvm->irq_srcu)) goto out_err_no_irq_srcu; + refcount_set(&kvm->users_count, 1); for (i = 0; i < KVM_ADDRESS_SPACE_NUM; i++) { struct kvm_memslots *slots = kvm_alloc_memslots(); @@ -667,7 +668,6 @@ static struct kvm *kvm_create_vm(unsigned long type) goto out_err_no_arch_destroy_vm; } - refcount_set(&kvm->users_count, 1); r = kvm_arch_init_vm(kvm, type); if (r) goto out_err_no_arch_destroy_vm; @@ -696,8 +696,8 @@ out_err: hardware_disable_all(); out_err_no_disable: kvm_arch_destroy_vm(kvm); - WARN_ON_ONCE(!refcount_dec_and_test(&kvm->users_count)); out_err_no_arch_destroy_vm: + WARN_ON_ONCE(!refcount_dec_and_test(&kvm->users_count)); for (i = 0; i < KVM_NR_BUSES; i++) kfree(kvm_get_bus(kvm, i)); for (i = 0; i < KVM_ADDRESS_SPACE_NUM; i++) -- cgit v1.2.3-59-g8ed1b