[PATCH 5.17 183/219] KVM: Dont create VM debugfs files outside of the VM directory

Greg Kroah-Hartman
2022-04-18T12:37:15Z

From: Oliver Upton <oupton@google.com>

commit a44a4cc1c969afec97dbb2aedaf6f38eaa6253bb upstream.

Unfortunately, there is no guarantee that KVM was able to instantiate a
debugfs directory for a particular VM. To that end, KVM shouldn't even
attempt to create new debugfs files in this case. If the specified
parent dentry is NULL, debugfs_create_file() will instantiate files at
the root of debugfs.

For arm64, it is possible to create the vgic-state file outside of a
VM directory, the file is not cleaned up when a VM is destroyed.
Nonetheless, the corresponding struct kvm is freed when the VM is
destroyed.

Nip the problem in the bud for all possible errant debugfs file
creations by initializing kvm->debugfs_dentry to -ENOENT. In so doing,
debugfs_create_file() will fail instead of creating the file in the root
directory.

Cc: stable@kernel.org
Fixes: 929f45e32499 ("kvm: no need to check return value of debugfs_create functions")
Signed-off-by: Oliver Upton <oupton@google.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20220406235615.1447180-2-oupton@google.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
virt/kvm/kvm_main.c | 10 ++++++++--
1 file changed, 8 insertions(+), 2 deletions(-)

--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -937,7 +937,7 @@ static void kvm_destroy_vm_debugfs(struc
int kvm_debugfs_num_entries = kvm_vm_stats_header.num_desc +
kvm_vcpu_stats_header.num_desc;

- if (!kvm->debugfs_dentry)
+ if (IS_ERR(kvm->debugfs_dentry))
return;

debugfs_remove_recursive(kvm->debugfs_dentry);
@@ -960,6 +960,12 @@ static int kvm_create_vm_debugfs(struct
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;

@@ -5484,7 +5490,7 @@ static void kvm_uevent_notify_change(uns
}
add_uevent_var(env, "PID=%d", kvm->userspace_pid);

- if (kvm->debugfs_dentry) {
+ if (!IS_ERR(kvm->debugfs_dentry)) {
char *tmp, *p = kmalloc(PATH_MAX, GFP_KERNEL_ACCOUNT);

if (p) {