Sorry,It does not need to be exported.
I have modified this patch and re-commit it.
Thank you very much for reminding.
thanks
Michael S. Tsirkin <mst@xxxxxxxxxx> 于2018年12月18日周二 下午12:38写道：
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
