Re: [PATCH 4.19 242/321] kvm: properly check debugfs dentry before using it

Pavel Machek
2019-12-05T22:29:32Z

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Hi!

> From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
>
> [ Upstream commit 8ed0579c12b2fe56a1fac2f712f58fc26c1dc49b ]
>
> debugfs can now report an error code if something went wrong instead of
> just NULL. So if the return value is to be used as a "real" dentry, it
> needs to be checked if it is an error before dereferencing it.
>
> This is now happening because of ff9fb72bc077 ("debugfs: return error
> values, not NULL"). syzbot has found a way to trigger multiple debugfs
> files attempting to be created, which fails, and then the error code
> gets passed to dentry_path_raw() which obviously does not like it.

4.19-stable does not contain patch ff9fb72bc077, so is this still good
idea? It should not break anything, as it still uses IS_ERR_OR_NULL,
but...

Best regards,
Pavel

> +++ b/virt/kvm/kvm_main.c
> @@ -3990,7 +3990,7 @@ 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_OR_NULL(kvm->debugfs_dentry)) {
> char *tmp, *p = kmalloc(PATH_MAX, GFP_KERNEL);
>
> if (p) {

--
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