Re: [PATCH AUTOSEL 4.19 40/57] kvm: properly check debugfs dentry before using it

Greg Kroah-Hartman
2019-03-30T05:43:57Z

On Fri, Mar 29, 2019 at 09:28:33PM -0400, Sasha Levin wrote:
> 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.
>
> Reported-by: Eric Biggers <ebiggers@kernel.org>
> Reported-and-tested-by: syzbot+7857962b4d45e602b8ad@syzkaller.appspotmail.com
> Cc: "Radim Krčmář" <rkrcmar@redhat.com>
> Cc: kvm@vger.kernel.org
> Acked-by: Paolo Bonzini <pbonzini@redhat.com>
> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
> Signed-off-by: Sasha Levin <sashal@kernel.org>
> ---
> virt/kvm/kvm_main.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index c436d95fd7aa..fb74f994cb63 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -3912,7 +3912,7 @@ 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) {
> --
> 2.19.1
>

Same thing here, this was a 5.0-only thing, no need for it to be
backported, please drop it from all trees.

thanks,

greg k-h