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    Subject[PATCH 5.15 117/230] KVM: Dont create VM debugfs files outside of the VM directory
    Date
    From: Oliver Upton <oupton@google.com>

    [ Upstream commit a44a4cc1c969afec97dbb2aedaf6f38eaa6253bb ]

    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: Sasha Levin <sashal@kernel.org>
    ---
    virt/kvm/kvm_main.c | 10 ++++++++--
    1 file changed, 8 insertions(+), 2 deletions(-)

    diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
    index 99c591569815..9134ae252d7c 100644
    --- a/virt/kvm/kvm_main.c
    +++ b/virt/kvm/kvm_main.c
    @@ -911,7 +911,7 @@ static void kvm_destroy_vm_debugfs(struct kvm *kvm)
    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);
    @@ -934,6 +934,12 @@ 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;

    @@ -5373,7 +5379,7 @@ static void kvm_uevent_notify_change(unsigned int type, struct kvm *kvm)
    }
    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) {
    --
    2.35.1


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