linux-kernel - Re: [PATCH] drm/nouveau/acr: Fix undefined behavior in nvkm_acr_hsfw_load

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Message-ID: <CADnq5_MnXG6-jzVZ7sXQjd8zeBKYPimFYOiR=M8=pB02fAxDzA@mail.gmail.com>
Date:   Fri, 28 Jan 2022 15:01:48 -0500
From:   Alex Deucher <alexdeucher@...il.com>
To:     Karol Herbst <kherbst@...hat.com>
Cc:     Lyude Paul <lyude@...hat.com>,
        Greg KH <gregkh@...uxfoundation.org>,
        Zhou Qingyang <zhou1615@....edu>,
        David Airlie <airlied@...ux.ie>,
        nouveau <nouveau@...ts.freedesktop.org>,
        Kangjie Lu <kjlu@....edu>, LKML <linux-kernel@...r.kernel.org>,
        Maling list - DRI developers 
        <dri-devel@...ts.freedesktop.org>, Ben Skeggs <bskeggs@...hat.com>
Subject: Re: [PATCH] drm/nouveau/acr: Fix undefined behavior in nvkm_acr_hsfw_load_bl()

On Fri, Jan 28, 2022 at 2:58 PM Karol Herbst <kherbst@...hat.com> wrote:
>
> On Fri, Jan 28, 2022 at 8:54 PM Alex Deucher <alexdeucher@...il.com> wrote:
> >
> > On Fri, Jan 28, 2022 at 2:20 PM Lyude Paul <lyude@...hat.com> wrote:
> > >
> > > Sigh-thank you for catching this - I had totally forgot about the umn.edu ban.
> > > I pushed this already but I will go ahead and send a revert for this patch.
> > > Will cc you on it as well.
> >
> > This seems short-sighted.  If the patch is valid I see no reason to
> > not accept it.  I'm not trying to downplay the mess umn got into, but
> > as long as the patch is well scrutinized and fixes a valid issue, it
> > should be applied rather than leaving potential bugs in place.
> >
> > Alex
> >
>
> Even though knowing that malicious code can be introduced via
> perfectly fine looking patches, and sometimes one will never spot the
> problem, this patch isn't all that bad tbh.
>
> So should we reject patches out of "policies" or should we just be
> extra careful? But not addressing the concerns as Greg pointed out is
> also kind of a bad move, but also not knowing what the state of
> resolving this mess is anyway.

I think if the umn mess taught us anything, it's the need for more
careful scrutiny.  But I certainly don't have the time to retype every
valid patch if it comes from a umn source.  There are also ethical
implications to that as well.  You didn't actually write the patch.

Alex

>
> >
> > >
> > > On Fri, 2022-01-28 at 11:18 +0100, Greg KH wrote:
> > > > On Tue, Jan 25, 2022 at 12:58:55AM +0800, Zhou Qingyang wrote:
> > > > > In nvkm_acr_hsfw_load_bl(), the return value of kmalloc() is directly
> > > > > passed to memcpy(), which could lead to undefined behavior on failure
> > > > > of kmalloc().
> > > > >
> > > > > Fix this bug by using kmemdup() instead of kmalloc()+memcpy().
> > > > >
> > > > > This bug was found by a static analyzer.
> > > > >
> > > > > Builds with 'make allyesconfig' show no new warnings,
> > > > > and our static analyzer no longer warns about this code.
> > > > >
> > > > > Fixes: 22dcda45a3d1 ("drm/nouveau/acr: implement new subdev to replace
> > > > > "secure boot"")
> > > > > Signed-off-by: Zhou Qingyang <zhou1615@....edu>
> > > > > ---
> > > > > The analysis employs differential checking to identify inconsistent
> > > > > security operations (e.g., checks or kfrees) between two code paths
> > > > > and confirms that the inconsistent operations are not recovered in the
> > > > > current function or the callers, so they constitute bugs.
> > > > >
> > > > > Note that, as a bug found by static analysis, it can be a false
> > > > > positive or hard to trigger. Multiple researchers have cross-reviewed
> > > > > the bug.
> > > > >
> > > > >  drivers/gpu/drm/nouveau/nvkm/subdev/acr/hsfw.c | 9 +++++----
> > > > >  1 file changed, 5 insertions(+), 4 deletions(-)
> > > > >
> > > > > diff --git a/drivers/gpu/drm/nouveau/nvkm/subdev/acr/hsfw.c
> > > > > b/drivers/gpu/drm/nouveau/nvkm/subdev/acr/hsfw.c
> > > > > index 667fa016496e..a6ea89a5d51a 100644
> > > > > --- a/drivers/gpu/drm/nouveau/nvkm/subdev/acr/hsfw.c
> > > > > +++ b/drivers/gpu/drm/nouveau/nvkm/subdev/acr/hsfw.c
> > > > > @@ -142,11 +142,12 @@ nvkm_acr_hsfw_load_bl(struct nvkm_acr *acr, const
> > > > > char *name, int ver,
> > > > >
> > > > >         hsfw->imem_size = desc->code_size;
> > > > >         hsfw->imem_tag = desc->start_tag;
> > > > > -       hsfw->imem = kmalloc(desc->code_size, GFP_KERNEL);
> > > > > -       memcpy(hsfw->imem, data + desc->code_off, desc->code_size);
> > > > > -
> > > > > +       hsfw->imem = kmemdup(data + desc->code_off, desc->code_size,
> > > > > GFP_KERNEL);
> > > > >         nvkm_firmware_put(fw);
> > > > > -       return 0;
> > > > > +       if (!hsfw->imem)
> > > > > +               return -ENOMEM;
> > > > > +       else
> > > > > +               return 0;
> > > > >  }
> > > > >
> > > > >  int
> > > > > --
> > > > > 2.25.1
> > > > >
> > > >
> > > > As stated before, umn.edu is still not allowed to contribute to the
> > > > Linux kernel.  Please work with your administration to resolve this
> > > > issue.
> > > >
> > >
> > > --
> > > Cheers,
> > >  Lyude Paul (she/her)
> > >  Software Engineer at Red Hat
> > >
> >
>