linux-kernel - Re: [PATCH 000/190] Revertion of all of the umn.edu commits

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Date:   Wed, 21 Apr 2021 17:47:10 +0200 (CEST)
From:   Jiri Kosina <jikos@...nel.org>
To:     Qiushi Wu <wu000273@....edu>
cc:     Kangjie Lu <kjlu@....edu>, Guenter Roeck <linux@...ck-us.net>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        open list <linux-kernel@...r.kernel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Aditya Pakki <pakki001@....edu>, x86@...nel.org,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Arnd Bergmann <arnd@...db.de>, David Airlie <airlied@...ux.ie>,
        Michael Turquette <mturquette@...libre.com>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        Bartosz Golaszewski <bgolaszewski@...libre.com>,
        Daniel Vetter <daniel@...ll.ch>,
        Jean Delvare <jdelvare@...e.com>,
        Will Deacon <will@...nel.org>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Jakub Kicinski <kuba@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Johan Hovold <johan@...nel.org>,
        Jiri Slaby <jirislaby@...nel.org>,
        Pablo Neira Ayuso <pablo@...filter.org>,
        Johannes Berg <johannes@...solutions.net>,
        Takashi Iwai <tiwai@...e.com>
Subject: Re: [PATCH 000/190] Revertion of all of the umn.edu commits

On Wed, 21 Apr 2021, Qiushi Wu wrote:

> The function description of "kobject_init_and_add()" mentioned that "If 
> this function returns an error, kobject_put() must be called to properly 
> clean up the memory associated with the object." (see 
> https://elixir.bootlin.com/linux/v5.12-rc8/source/lib/kobject.c#L464) So 
> we use this patch to fix the issue, and I may miss some context here, 
> but I don't see why this cause some issue like NULL dereferences.
> 
> The identification methodology for this bug and other similar bugs that
> are error-handling related, is shown in "Understanding and Detecting
> Disordered Error Handling with Precise Function Pairing."
> (https://www.usenix.org/conference/usenixsecurity21/presentation/wu-qiushi)

You are calling kobject_put() if kobject_init_and_add() fails. That will 
in turn invoke pci_slot_release() which will try to delete slot->list, but 
that hasn't been initialized yet. 

Fixed in 4684709bf8, present in two major Linux kernel releases.

-- 
Jiri Kosina
SUSE Labs