linux-kernel - Re: [PATCH] ppdev: fix double-free of pp->pdev->name

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Message-ID: <20161030180036.GC2558@pc.thejh.net>
Date:   Sun, 30 Oct 2016 19:00:36 +0100
From:   Jann Horn <jann@...jh.net>
To:     Sudip Mukherjee <sudipm.mukherjee@...il.com>
Cc:     Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org, linux-parport@...ts.infradead.org,
        Andy Lutomirski <luto@...capital.net>
Subject: Re: [PATCH] ppdev: fix double-free of pp->pdev->name

On Sun, Oct 30, 2016 at 11:24:27PM +0530, Sudip Mukherjee wrote:
> On Sunday 30 October 2016 09:14 PM, Jann Horn wrote:
> >free_pardevice() is called by parport_unregister_device() and already frees
> >pp->pdev->name, don't try to do it again.
> >
> >This bug causes kernel crashes.
> >
> >I found and verified this with KASAN and some added pr_emerg()s:
> >
> >[   60.316568] pp_release: pp->pdev->name == ffff88039cb264c0
> >[   60.316692] free_pardevice: freeing par_dev->name at ffff88039cb264c0
> >[   60.316706] pp_release: kfree(ffff88039cb264c0)
> >[   60.316714] ==========================================================
> >[   60.316722] BUG: Double free or freeing an invalid pointer
> >[   60.316731] Unexpected shadow byte: 0xFB
> >[   60.316801] Object at ffff88039cb264c0, in cache kmalloc-32 size: 32
> >[   60.316813] Allocated:
> >[   60.316824] PID = 1695
> >[   60.316869] Freed:
> >[   60.316880] PID = 1695
> >[   60.316935] ==========================================================
> >
> >CCing Andy Lutomirski because I think this is what broke vmapped stacks
> >for me - after applying this patch, vmapped stacks worked for me.
> >Previously, I got oopses (and lockups) caused by area->pages[0] being
> >0x400000000 in __vunmap(), with area->pages being allocated in the kmalloc
> >area.
> 
> I think the above should not be a part of the commit message.

Ah, yes.

@maintainers: Feel free to remove that from the commit message. Or should I
resend?

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