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Fri, 09 Oct 2026 16:22:12 -0700 (PDT) Message-ID: <929077046827f363bc32f6f59e760de27a48b5ff.camel@redhat.com> Subject: Re: [PATCH 1/2] drm/nouveau/sw: prevent NULL deref of disp in vblank methods From: lyude@redhat.com To: Zhenhao Wan , Danilo Krummrich , Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , David Airlie , Simona Vetter Cc: dri-devel@lists.freedesktop.org, nouveau@lists.freedesktop.org, linux-kernel@vger.kernel.org, Yuhao Jiang , stable@vger.kernel.org Date: Fri, 09 Oct 2026 19:22:11 -0400 In-Reply-To: <20260812-nouveau-nvkm-absent-subdev-null-deref-v1-1-7e057f6aeba0@gmail.com> References: <20260812-nouveau-nvkm-absent-subdev-null-deref-v1-0-7e057f6aeba0@gmail.com> <20260812-nouveau-nvkm-absent-subdev-null-deref-v1-1-7e057f6aeba0@gmail.com> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.58.3 (3.58.3-2.fc43) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Reviewed-by: Lyude Paul Will push to drm-misc-next in a moment On Wed, 2026-08-12 at 23:00 +0800, Zhenhao Wan wrote: > The NV50 and GF100 software-class vblank methods nv50_sw_chan_mthd() > and gf100_sw_chan_mthd() evaluate "data < device->disp- > >vblank.index_nr" > to validate the requested vblank head before allowing its notifier. >=20 > On a headless card the display subdevice is absent: > nvkm_subdev_disable() > (strap-driven from devinit) and the -ENODEV path of the > NVKM_LAYOUT_ONCE > device constructor both leave device->disp =3D=3D NULL while the device > continues to probe and still registers a render node (DRIVER_RENDER). > An > unprivileged client holding a /dev/dri/renderD* fd can then create a > software channel and push method 0x0408 (NV50) / 0x040c (GF100), > which > dereferences the NULL device->disp and oopses the kernel. >=20 > The channel constructors nv50_sw_chan_new() and gf100_sw_chan_new() > already tolerate an absent display ("for (i =3D 0; disp && ...)"), so > no > vblank notifier is ever registered on such a card and the method > handlers > are the only path that assumes disp is present. Guard the dereference > with the same disp NULL test the constructors already use. >=20 > Reported-by: Yuhao Jiang > Assisted-by: Claude:claude-opus-5 > Cc: stable@vger.kernel.org > Signed-off-by: Zhenhao Wan > --- > =C2=A0drivers/gpu/drm/nouveau/nvkm/engine/sw/gf100.c | 2 +- > =C2=A0drivers/gpu/drm/nouveau/nvkm/engine/sw/nv50.c=C2=A0 | 2 +- > =C2=A02 files changed, 2 insertions(+), 2 deletions(-) >=20 > diff --git a/drivers/gpu/drm/nouveau/nvkm/engine/sw/gf100.c > b/drivers/gpu/drm/nouveau/nvkm/engine/sw/gf100.c > index 0171cdf6f639..4cf8cd120c76 100644 > --- a/drivers/gpu/drm/nouveau/nvkm/engine/sw/gf100.c > +++ b/drivers/gpu/drm/nouveau/nvkm/engine/sw/gf100.c > @@ -72,7 +72,7 @@ gf100_sw_chan_mthd(struct nvkm_sw_chan *base, int > subc, u32 mthd, u32 data) > =C2=A0 chan->vblank.value =3D data; > =C2=A0 return true; > =C2=A0 case 0x040c: > - if (data < device->disp->vblank.index_nr) { > + if (device->disp && data < device->disp- > >vblank.index_nr) { > =C2=A0 nvkm_event_ntfy_allow(&chan- > >vblank.notify[data]); > =C2=A0 return true; > =C2=A0 } > diff --git a/drivers/gpu/drm/nouveau/nvkm/engine/sw/nv50.c > b/drivers/gpu/drm/nouveau/nvkm/engine/sw/nv50.c > index 0cfb1eaae6de..b202e11238a5 100644 > --- a/drivers/gpu/drm/nouveau/nvkm/engine/sw/nv50.c > +++ b/drivers/gpu/drm/nouveau/nvkm/engine/sw/nv50.c > @@ -69,7 +69,7 @@ nv50_sw_chan_mthd(struct nvkm_sw_chan *base, int > subc, u32 mthd, u32 data) > =C2=A0 case 0x0400: chan->vblank.offset =3D data; return true; > =C2=A0 case 0x0404: chan->vblank.value=C2=A0 =3D data; return true; > =C2=A0 case 0x0408: > - if (data < device->disp->vblank.index_nr) { > + if (device->disp && data < device->disp- > >vblank.index_nr) { > =C2=A0 nvkm_event_ntfy_allow(&chan- > >vblank.notify[data]); > =C2=A0 return true; > =C2=A0 }