From: Sean Christopherson seanjc@google.com
[ Upstream commit 5c697c367a66307a5d943c3449421aff2aa3ca4a ]
Initialize debugfs_entry to its semi-magical -ENOENT value when the VM is created. KVM's teardown when VM creation fails is kludgy and calls kvm_uevent_notify_change() and kvm_destroy_vm_debugfs() even if KVM never attempted kvm_create_vm_debugfs(). Because debugfs_entry is zero initialized, the IS_ERR() checks pass and KVM derefs a NULL pointer.
BUG: kernel NULL pointer dereference, address: 0000000000000018 #PF: supervisor read access in kernel mode #PF: error_code(0x0000) - not-present page PGD 1068b1067 P4D 1068b1067 PUD 1068b0067 PMD 0 Oops: 0000 [#1] SMP CPU: 0 PID: 871 Comm: repro Not tainted 5.18.0-rc1+ #825 Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/2015 RIP: 0010:__dentry_path+0x7b/0x130 Call Trace: <TASK> dentry_path_raw+0x42/0x70 kvm_uevent_notify_change.part.0+0x10c/0x200 [kvm] kvm_put_kvm+0x63/0x2b0 [kvm] kvm_dev_ioctl+0x43a/0x920 [kvm] __x64_sys_ioctl+0x83/0xb0 do_syscall_64+0x31/0x50 entry_SYSCALL_64_after_hwframe+0x44/0xae </TASK> Modules linked in: kvm_intel kvm irqbypass
Fixes: a44a4cc1c969 ("KVM: Don't create VM debugfs files outside of the VM directory") Cc: stable@vger.kernel.org Cc: Marc Zyngier maz@kernel.org Cc: Oliver Upton oupton@google.com Reported-by: syzbot+df6fbbd2ee39f21289ef@syzkaller.appspotmail.com Signed-off-by: Sean Christopherson seanjc@google.com Reviewed-by: Oliver Upton oupton@google.com Message-Id: 20220415004622.2207751-1-seanjc@google.com Signed-off-by: Paolo Bonzini pbonzini@redhat.com Signed-off-by: Sasha Levin sashal@kernel.org --- virt/kvm/kvm_main.c | 12 ++++++------ 1 file changed, 6 insertions(+), 6 deletions(-)
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c index 9134ae252d7c..9eac68ae291e 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -934,12 +934,6 @@ static int kvm_create_vm_debugfs(struct kvm *kvm, int fd) int kvm_debugfs_num_entries = kvm_vm_stats_header.num_desc + kvm_vcpu_stats_header.num_desc;
- /* - * Force subsequent debugfs file creations to fail if the VM directory - * is not created. - */ - kvm->debugfs_dentry = ERR_PTR(-ENOENT); - if (!debugfs_initialized()) return 0;
@@ -1055,6 +1049,12 @@ static struct kvm *kvm_create_vm(unsigned long type)
BUILD_BUG_ON(KVM_MEM_SLOTS_NUM > SHRT_MAX);
+ /* + * Force subsequent debugfs file creations to fail if the VM directory + * is not created (by kvm_create_vm_debugfs()). + */ + kvm->debugfs_dentry = ERR_PTR(-ENOENT); + if (init_srcu_struct(&kvm->srcu)) goto out_err_no_srcu; if (init_srcu_struct(&kvm->irq_srcu))