linux-kernel - Re: [PATCH] zram: fix null dereference of handle

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Message-ID: <20170920062821.GC6298@jagdpanzerIV.localdomain>
Date:   Wed, 20 Sep 2017 15:28:21 +0900
From:   Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
To:     Minchan Kim <minchan@...nel.org>
Cc:     Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-kernel@...r.kernel.org, kernel-team <kernel-team@....com>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>
Subject: Re: [PATCH] zram: fix null dereference of handle

Hello,

On (09/20/17 14:51), Minchan Kim wrote:
> On Tue, Sep 19, 2017 at 07:21:25PM +0900, Sergey Senozhatsky wrote:
> > Minchan,
> > 
> > I just ran across it [because I had a bug to analize where this
> > part was involved]. I'd really prefer the kernel to BUG_ON immediately
> > instead of dying in agony.
> > 
> > can we, please, return BUG_ON() back?
> > 
> > there is no point in trying to save the kernel once it did that type
> > of violation.
> 
> I agree. If it happens, it would corrupt other user's buffer which ends
> up leaking some private data from others so there is pointless to keep
> system alive to debug it.

thanks!

yep, I guess we are also potentially looking at __zs_map_object()
preempting zsmalloc in normal context, which would overwrite
area->vm_addr from IRQ, map it, use it, unmap it in __zs_unmap_object().
and then resumed normal context will attempt to use unmapped area->vm_addr,
I suppose.


> Do you mind sending a formal patch?

sure, will do.

	-ss