linux-kernel - Re: [PATCH v2] ppdev: fix double-free of pp->pdev->name

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Date:   Thu, 10 Nov 2016 12:40:40 +0000
From:   Sudip Mukherjee <sudipm.mukherjee@...il.com>
To:     Jann Horn <jann@...jh.net>
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 v2] ppdev: fix double-free of pp->pdev->name

On Sun, Oct 30, 2016 at 11:19:24PM +0100, 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] ==========================================================
> 
> Signed-off-by: Jann Horn <jann@...jh.net>
Acked-by: Sudip Mukherjee <sudipm.mukherjee@...il.com>