On Tue, Dec 18, 2018 at 11:42:11AM +0800, gchen.guomin@xxxxxxxxx wrote: > From: guomin chen <gchen.guomin@xxxxxxxxx> > > When mm->owner is modified by exit_mm, if the new owner directly calls > unuse_mm to exit, it will cause Use-After-Free. Due to the unuse_mm() > directly sets tsk->mm=NULL. > > Under normal circumstances,When do_exit exits, mm->owner will > be updated on exit_mm(). but when the kernel process calls > unuse_mm() and then exits,mm->owner cannot be updated. And it > will point to a task that has been released. > > The current issue flow is as follows: > Process C Process A Process B > qemu-system-x86_64: kernel:vhost_net kernel: vhost_net > open /dev/vhost-net > VHOST_SET_OWNER create kthread vhost-%d create kthread vhost-%d > network init use_mm() use_mm() > ... ... > Abnormal exited > ... > do_exit > exit_mm() > update mm->owner to A > exit_files() > close_files() > kthread_should_stop() unuse_mm() > Stop Process A tsk->mm=NULL > do_exit() > can't update owner > A exit completed vhost-%d rcv first package > vhost-%d build rcv buffer for vq > page fault > access mm & mm->owner > NOW,mm->owner still pointer A > kernel UAF > stop Process B > > Although I am having this issue on vhost_net,But it affects all users of > unuse_mm. > > Cc: "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx> > Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> > Cc: "Luis R. Rodriguez" <mcgrof@xxxxxxxxxx> > Cc: Dominik Brodowski <linux@xxxxxxxxxxxxxxxxxxxx> > Cc: Arnd Bergmann <arnd@xxxxxxxx> > Cc: linux-kernel@xxxxxxxxxxxxxxx > Cc: linux-mm@xxxxxxxxx > Cc: "Michael S. Tsirkin" <mst@xxxxxxxxxx> > Cc: Jason Wang <jasowang@xxxxxxxxxx> > Cc: Christoph Hellwig <hch@xxxxxxxxxxxxx> > Signed-off-by: guomin chen <gchen.guomin@xxxxxxxxx> > --- > kernel/exit.c | 1 + > mm/mmu_context.c | 1 + > 2 files changed, 2 insertions(+) > > diff --git a/kernel/exit.c b/kernel/exit.c > index 0e21e6d..9e046dd 100644 > --- a/kernel/exit.c > +++ b/kernel/exit.c > @@ -486,6 +486,7 @@ void mm_update_next_owner(struct mm_struct *mm) > task_unlock(c); > put_task_struct(c); > } > +EXPORT_SYMBOL(mm_update_next_owner); > #endif /* CONFIG_MEMCG */ > > /* So why export it? Is that still needed? > diff --git a/mm/mmu_context.c b/mm/mmu_context.c > index 3e612ae..9eb81aa 100644 > --- a/mm/mmu_context.c > +++ b/mm/mmu_context.c > @@ -60,5 +60,6 @@ void unuse_mm(struct mm_struct *mm) > /* active_mm is still 'mm' */ > enter_lazy_tlb(mm, tsk); > task_unlock(tsk); > + mm_update_next_owner(mm); > } > EXPORT_SYMBOL_GPL(unuse_mm); > -- > 1.8.3.1
