linux-kernel - Re: [PATCH] PCI: endpoint: Fix use after free in pci_epf_remove

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Message-ID: <CANXvt5r-1+W91DXNcVuRxTE0_T0TSGuduMhOfmYgY=N87uzqCg@mail.gmail.com>
Date:   Tue, 7 Dec 2021 16:44:05 +0900
From:   Shunsuke Mie <mie@...l.co.jp>
To:     Kishon Vijay Abraham I <kishon@...com>
Cc:     Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Bjorn Helgaas <bhelgaas@...gle.com>, linux-pci@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        stable@...r.kernel.org
Subject: Re: [PATCH] PCI: endpoint: Fix use after free in pci_epf_remove_cfs()

Hi Kishon,

2021年12月7日(火) 16:26 Kishon Vijay Abraham I <kishon@...com>:
>
> Hi Shunsuke,
>
> On 21/06/21 12:30 pm, Shunsuke Mie wrote:
> > All of entries are freed in a loop, however, the freed entry is accessed
> > by list_del() after the loop.
> >
> > When epf driver that includes pci-epf-test unload, the pci_epf_remove_cfs()
> > is called, and occurred the use after free. Therefore, kernel panics
> > randomly after or while the module unloading.
> >
> > I tested this patch with r8a77951-Salvator-xs boards.
>
> Can you provide the crash dump?
Ok. However, that is use-after-free bug. so, the crash log is changed randomly.
I'll send some crash dumps.
> >
> > Fixes: ef1433f ("PCI: endpoint: Create configfs entry for each pci_epf_device_id table entry")
> > Signed-off-by: Shunsuke Mie <mie@...l.co.jp>
> > ---
> >  drivers/pci/endpoint/pci-epf-core.c | 4 +++-
> >  1 file changed, 3 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/pci/endpoint/pci-epf-core.c b/drivers/pci/endpoint/pci-epf-core.c
> > index e9289d10f822..538e902b0ba6 100644
> > --- a/drivers/pci/endpoint/pci-epf-core.c
> > +++ b/drivers/pci/endpoint/pci-epf-core.c
> > @@ -202,8 +202,10 @@ static void pci_epf_remove_cfs(struct pci_epf_driver *driver)
> >               return;
> >
> >       mutex_lock(&pci_epf_mutex);
> > -     list_for_each_entry_safe(group, tmp, &driver->epf_group, group_entry)
> > +     list_for_each_entry_safe(group, tmp, &driver->epf_group, group_entry) {
> > +             list_del(&group->group_entry);
>
> Need full crash dump to see if this is really required or not. Ideally this
> should be handled by configfs (or a configfs API could be used).
>
> Thanks,
> Kishon