From: Nicolai Stange <nstange@suse.de>
To: Johannes Berg <johannes@sipsolutions.net>
Cc: David Laight <David.Laight@ACULAB.COM>,
'Taehee Yoo' <ap420073@gmail.com>,
"davem@davemloft.net" <davem@davemloft.net>,
"kuba@kernel.org" <kuba@kernel.org>,
"netdev@vger.kernel.org" <netdev@vger.kernel.org>,
Nicolai Stange <nstange@suse.de>,
"linux-wireless@vger.kernel.org" <linux-wireless@vger.kernel.org>,
"wil6210@qti.qualcomm.com" <wil6210@qti.qualcomm.com>,
"brcm80211-dev-list@cypress.com" <brcm80211-dev-list@cypress.com>,
"b43-dev@lists.infradead.org" <b43-dev@lists.infradead.org>,
"linux-bluetooth@vger.kernel.org"
<linux-bluetooth@vger.kernel.org>
Subject: [PATCH net 000/117] net: avoid to remove module when its debugfs is being used
Date: Fri, 09 Oct 2020 07:09:01 +0200 [thread overview]
Message-ID: <87v9fkgf4i.fsf@suse.de> (raw)
In-Reply-To: <62f6c2bd11ed8b25c1cd4462ebc6db870adc4229.camel@sipsolutions.net> (Johannes Berg's message of "Thu, 08 Oct 2020 18:14:15 +0200")
Johannes Berg <johannes@sipsolutions.net> writes:
> On Thu, 2020-10-08 at 15:59 +0000, David Laight wrote:
>> From: Taehee Yoo
>> > Sent: 08 October 2020 16:49
>> >
>> > When debugfs file is opened, its module should not be removed until
>> > it's closed.
>> > Because debugfs internally uses the module's data.
>> > So, it could access freed memory.
>> >
>> > In order to avoid panic, it just sets .owner to THIS_MODULE.
>> > So that all modules will be held when its debugfs file is opened.
>>
>> Can't you fix it in common code?
Probably not: it's the call to ->release() that's faulting in the Oops
quoted in the cover letter and that one can't be protected by the
core debugfs code, unfortunately.
There's a comment in full_proxy_release(), which reads as
/*
* We must not protect this against removal races here: the
* original releaser should be called unconditionally in order
* not to leak any resources. Releasers must not assume that
* ->i_private is still being meaningful here.
*/
> Yeah I was just wondering that too - weren't the proxy_fops even already
> intended to fix this?
No, as far as file_operations are concerned, the proxy fops's intent was
only to ensure that the memory the file_operations' ->owner resides in
is still valid so that try_module_get() won't splat at file open
(c.f. [1]).
You're right that the default "full" proxy fops do prevent all
file_operations but ->release() from getting invoked on removed files,
but the motivation had not been to protect the file_operations
themselves, but accesses to any stale data associated with removed files
([2]).
> The modules _should_ be removing the debugfs files, and then the
> proxy_fops should kick in, no?
No, as said, not for ->release(). I haven't looked into the inidividual
patches here, but setting ->owner indeed sounds like the right thing to
do.
But you're right that modules should be removing any left debugfs files
at exit.
Thanks,
Nicolai
[1] 9fd4dcece43a ("debugfs: prevent access to possibly dead
file_operations at file open")
[2] 49d200deaa68 ("debugfs: prevent access to removed files' private data")
--
SUSE Software Solutions Germany GmbH, Maxfeldstr. 5, 90409 N?rnberg, Germany
(HRB 36809, AG N?rnberg), GF: Felix Imend?rffer
next prev parent reply other threads:[~2020-10-09 5:09 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-08 15:48 [PATCH net 000/117] net: avoid to remove module when its debugfs is being used Taehee Yoo
2020-10-08 15:59 ` David Laight
2020-10-08 16:14 ` Johannes Berg
2020-10-08 16:37 ` Taehee Yoo
2020-10-09 5:38 ` Nicolai Stange
2020-10-09 10:07 ` Taehee Yoo
2020-10-09 5:09 ` Nicolai Stange [this message]
2020-10-09 7:45 ` Johannes Berg
2020-10-09 10:15 ` Taehee Yoo
2020-10-09 10:21 ` Johannes Berg
2020-10-09 15:33 ` Steve deRosier
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=87v9fkgf4i.fsf@suse.de \
--to=nstange@suse.de \
--cc=David.Laight@ACULAB.COM \
--cc=ap420073@gmail.com \
--cc=b43-dev@lists.infradead.org \
--cc=brcm80211-dev-list@cypress.com \
--cc=davem@davemloft.net \
--cc=johannes@sipsolutions.net \
--cc=kuba@kernel.org \
--cc=linux-bluetooth@vger.kernel.org \
--cc=linux-wireless@vger.kernel.org \
--cc=netdev@vger.kernel.org \
--cc=wil6210@qti.qualcomm.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 a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).