From: Tilman Schmidt <tilman@imap.cc>
To: Paul Bolle <pebolle@tiscali.nl>, netdev@vger.kernel.org
Cc: Peter Hurley <peter@hurleysoftware.com>,
Sasha Levin <sasha.levin@oracle.com>,
syzkaller@googlegroups.com, David Miller <davem@davemloft.net>,
Karsten Keil <isdn@linux-pingi.de>,
isdn4linux@listserv.isdn4linux.de,
gigaset307x-common@lists.sourceforge.net,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH 2/3] ser_gigaset: fix deallocation of platform device structure
Date: Wed, 9 Dec 2015 12:10:29 +0100 [thread overview]
Message-ID: <56680C25.1050704@imap.cc> (raw)
In-Reply-To: <1449616321.2384.36.camel@tiscali.nl>
[-- Attachment #1: Type: text/plain, Size: 2179 bytes --]
Am 09.12.2015 um 00:12 schrieb Paul Bolle:
>> --- a/drivers/isdn/gigaset/ser-gigaset.c
>> +++ b/drivers/isdn/gigaset/ser-gigaset.c
>> @@ -370,19 +370,23 @@ static void gigaset_freecshw(struct cardstate
>> *cs)
>> tasklet_kill(&cs->write_tasklet);
>> if (!cs->hw.ser)
>> return;
>> - dev_set_drvdata(&cs->hw.ser->dev.dev, NULL);
>> platform_device_unregister(&cs->hw.ser->dev);
>> - kfree(cs->hw.ser);
>> - cs->hw.ser = NULL;
>> }
>>
>> static void gigaset_device_release(struct device *dev)
>> {
>> struct platform_device *pdev = to_platform_device(dev);
>> + struct cardstate *cs = dev_get_drvdata(dev);
>>
>> /* adapted from platform_device_release() in
>> drivers/base/platform.c */
>> kfree(dev->platform_data);
>> kfree(pdev->resource);
>> +
>> + if (!cs)
>> + return;
>> + dev_set_drvdata(dev, NULL);
>
> dev equals cs->hw.ser->dev.dev, doesn't it?
Correct.
> So what does setting
> cs->hw.ser->dev.dev.driver_data to NULL just before freeing it buy us?
We're freeing cs->hw.ser, not cs->hw.ser->dev.
Clearing the reference to cs from the device structure before freeing cs
guards against possible use-after-free.
>> + kfree(cs->hw.ser);
>> + cs->hw.ser = NULL;
>
> I might be missing something, but what does setting this to NULL buy us
> here?
Just defensive programming. Guarding against possible use-after-free or
double-free.
>
> (I realize that I'm asking questions to code that isn't actually new but
> only moved around, but I think that's still an opportunity to have
> another look at that code.)
I'm a big fan of one change per patch. If we also want to modify the
moved code then that should be done in a separate patch. It makes
bisecting so much easier. Same reason why I separated out patch 3/3. And
btw same reason why I think patch 1/3 should go in as-is, as an obvious
fix to commit f34d7a5b, and any concerns about whether those tests are
useful should be addressed by a separate patch.
Regards,
Tilman
--
Tilman Schmidt E-Mail: tilman@imap.cc
Bonn, Germany
Nous, on a des fleurs et des bougies pour nous protéger.
[-- Attachment #2: OpenPGP digital signature --]
[-- Type: application/pgp-signature, Size: 473 bytes --]
next prev parent reply other threads:[~2015-12-09 11:10 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-12-08 11:00 [PATCH 0/3] ser_gigaset fixes Tilman Schmidt
2015-12-08 11:00 ` [PATCH 1/3] ser_gigaset: fix up NULL checks Tilman Schmidt
2015-12-08 19:45 ` Paul Bolle
2015-12-08 22:16 ` One Thousand Gnomes
2015-12-09 10:45 ` Tilman Schmidt
2015-12-09 12:12 ` One Thousand Gnomes
2015-12-09 19:18 ` Paul Bolle
2015-12-08 11:00 ` [PATCH 2/3] ser_gigaset: fix deallocation of platform device structure Tilman Schmidt
2015-12-08 23:12 ` Paul Bolle
2015-12-09 11:10 ` Tilman Schmidt [this message]
2015-12-10 11:20 ` Paul Bolle
2015-12-10 14:04 ` Peter Hurley
2015-12-12 17:52 ` Tilman Schmidt
2015-12-08 11:00 ` [PATCH 3/3] ser_gigaset: remove unnecessary kfree() calls from release method Tilman Schmidt
2015-12-08 23:15 ` Paul Bolle
2015-12-10 11:31 ` [PATCH 0/3] ser_gigaset fixes Paul Bolle
2015-12-12 18:09 ` Tilman Schmidt
2015-12-12 18:32 ` Paul Bolle
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=56680C25.1050704@imap.cc \
--to=tilman@imap.cc \
--cc=davem@davemloft.net \
--cc=gigaset307x-common@lists.sourceforge.net \
--cc=isdn4linux@listserv.isdn4linux.de \
--cc=isdn@linux-pingi.de \
--cc=linux-kernel@vger.kernel.org \
--cc=netdev@vger.kernel.org \
--cc=pebolle@tiscali.nl \
--cc=peter@hurleysoftware.com \
--cc=sasha.levin@oracle.com \
--cc=syzkaller@googlegroups.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.