linux-kernel - Re: [BUG] char: pcmcia: a possible concurrency double-free bug in rx_alloc

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Date:   Mon, 7 Jan 2019 09:57:24 +0100
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Jia-Ju Bai <baijiaju1990@...il.com>
Cc:     arnd@...db.de, viro@...iv.linux.org.uk,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [BUG] char: pcmcia: a possible concurrency double-free bug in
 rx_alloc_buffers()

On Mon, Jan 07, 2019 at 04:12:22PM +0800, Jia-Ju Bai wrote:
> In drivers/char/pcmcia/synclink_cs.c, the functions mgslpc_open() and hdlcdev_open() can be concurrently executed.
> 
> hdlcdev_open
>   startup
>     claim_resources
>       rx_alloc_buffers
>         line 2641: kfree(info->rx_buf)
> 
> mgslpc_open
>   startup
>     claim_resources
>       rx_alloc_buffers
>         line 2641: kfree(info->rx_buf)
> 
> Thus, a possible concurrency double-free bug may occur.

Wait, are you sure those really are the same structure, and that those
two functions can be called at the same time?  That is a tty and a
network device, are they both created at the same time or does opening
one create the other?

It's not obvious in looking at the code if this really is the same
structure or not, how did your tool figure it out?

thanks,

greg k-h