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Date:   Thu, 15 Sep 2022 22:03:33 -0700
From:   Hyunwoo Kim <imv4bel@gmail.com>
To:     Dominik Brodowski <linux@dominikbrodowski.net>
Cc:     Arnd Bergmann <arnd@arndb.de>, laforge@gnumonks.org,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Ilpo =?iso-8859-1?Q?J=E4rvinen?= <ilpo.jarvinen@linux.intel.com>,
        linux-kernel@vger.kernel.org, Paul Fulghum <paulkf@microgate.com>,
        akpm@osdl.org, Lubomir Rintel <lkundrak@v3.sk>, imv4bel@gmail.com
Subject: Re: [PATCH] pcmcia: synclink_cs: Fix use-after-free in mgslpc_ioctl()
Message-ID: <20220916050333.GA188358@ubuntu>
References: <20220913052020.GA85241@ubuntu>
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 <20220915020834.GA110086@ubuntu>
 <f41c2765-80e0-48bc-b1e4-8cfd3230fd4a@www.fastmail.com>
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The previous mailing list is here:
https://lore.kernel.org/lkml/20220913052020.GA85241@ubuntu/#r


Dear all,


I reported that the scr24x_cs driver does not cause UAF, which is incorrect.

UAFs can also occur in the scr24x_cs driver in the following order:
```
                cpu0                                                cpu1
       1. open()
                                                             2. scr24x_remove()
                                                                device_destroy()
                                                                cdev_del()
                                                                kref_put()
       3. scr24x_open()
          kref_get()   <- refcount_t: addition on 0;
                                                             4. scr24x_delete()
                                                                kfree(dev);
       5. scr24x_read()    <- UAF
```
Because this driver uses kref_init, it looks as if no UAF is happening, but it does.

Since there is no lock between .open and .remove, kref_get() is called after kref_put() 
is called, so "refcount_t: addition on 0;" This is what happens.


So I submitted a patch for all drivers in this path:
- synclink_cs.c "v2" patch : https://lore.kernel.org/lkml/20220916045734.GA187909@ubuntu/T/#u
- cm4040_cs.c : https://lore.kernel.org/lkml/20220916045834.GA188033@ubuntu/T/#u
- cm4000_cs.c : https://lore.kernel.org/lkml/20220916045929.GA188153@ubuntu/T/#u
- scr24x_cs.c : https://lore.kernel.org/lkml/20220916050006.GA188273@ubuntu/T/#u


Best Regards,
Hyunwoo Kim.