linux-kernel - Re: [PATCH stable 4.4 v2] coredump: fix race condition between mmget_not_zero()/get_task

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Message-ID: <20190610141720.GB18446@mellanox.com>
Date:   Mon, 10 Jun 2019 14:17:25 +0000
From:   Jason Gunthorpe <jgg@...lanox.com>
To:     Michal Hocko <mhocko@...nel.org>
CC:     Stable tree <stable@...r.kernel.org>,
        Greg KH <gregkh@...uxfoundation.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Jann Horn <jannh@...gle.com>, Oleg Nesterov <oleg@...hat.com>,
        Peter Xu <peterx@...hat.com>,
        Mike Rapoport <rppt@...ux.ibm.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Joel Fernandes <joel@...lfernandes.org>
Subject: Re: [PATCH stable 4.4 v2] coredump: fix race condition between
 mmget_not_zero()/get_task_mm() and core dumping

On Mon, Jun 10, 2019 at 03:58:23PM +0200, Michal Hocko wrote:
> Just a heads up. Ajay Kaher has noticed that mlx4 driver is missing the
> check in 4.14 [1] and 4.4 seems to have the same problem. I will wait
> for more review before reposting v3. The incremental diff is:
> 
> diff --git a/drivers/infiniband/hw/mlx4/main.c b/drivers/infiniband/hw/mlx4/main.c
> index 67c4c73343d4..6968154a073e 100644
> +++ b/drivers/infiniband/hw/mlx4/main.c
> @@ -1042,6 +1042,8 @@ static void mlx4_ib_disassociate_ucontext(struct ib_ucontext *ibcontext)
>  	 * mlx4_ib_vma_close().
>  	 */
>  	down_write(&owning_mm->mmap_sem);
> +	if (!mmget_still_valid(owning_mm))
> +		goto skip_mm;
>  	for (i = 0; i < HW_BAR_COUNT; i++) {
>  		vma = context->hw_bar_info[i].vma;
>  		if (!vma)
> @@ -1061,6 +1063,7 @@ static void mlx4_ib_disassociate_ucontext(struct ib_ucontext *ibcontext)
>  		context->hw_bar_info[i].vma->vm_ops = NULL;
>  	}
>  
> +skip_mm:
>  	up_write(&owning_mm->mmap_sem);
>  	mmput(owning_mm);
>  	put_task_struct(owning_process);

Looks OK to me

Jason