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

[Sasha Levin]

On Sat, Mar 30, 2019 at 06:43:50AM +0100, Greg Kroah-Hartman wrote:
> On Fri, Mar 29, 2019 at 09:28:33PM -0400, Sasha Levin wrote:
> > From: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> >
> > [ 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@xxxxxxxxxx>
> > Reported-and-tested-by: syzbot+7857962b4d45e602b8ad@xxxxxxxxxxxxxxxxxxxxxxxxx
> > Cc: "Radim KrÄmÃÅ" <rkrcmar@xxxxxxxxxx>
> > Cc: kvm@xxxxxxxxxxxxxxx
> > Acked-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
> > Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> > Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
> > Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
> > ---
> >  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.

Dropped, thanks!

--
Thanks,
Sasha