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Wed, 14 Aug 2019 07:39:22 -0700 (PDT) Date: Wed, 14 Aug 2019 07:39:20 -0700 From: Guenter Roeck To: Neil Armstrong Cc: Geert Uytterhoeven , Andrzej Pietrasiewicz , Andrzej Hajda , Laurent Pinchart , Jonas Karlman , Jernej Skrabec , David Airlie , Daniel Vetter , Sam Ravnborg , Emil Velikov , dri-devel@lists.freedesktop.org, linux-renesas-soc@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] drm/bridge: dumb-vga-dac: Fix dereferencing -ENODEV DDC channel Message-ID: <20190814143920.GA30613@roeck-us.net> References: <20190813093046.4976-1-geert+renesas@glider.be> <29ff3bfd-57ee-9c64-3706-555edc8b4675@baylibre.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <29ff3bfd-57ee-9c64-3706-555edc8b4675@baylibre.com> User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Aug 13, 2019 at 02:01:26PM +0200, Neil Armstrong wrote: > Hi, > > > On 13/08/2019 11:30, Geert Uytterhoeven wrote: > > If the VGA connector has no DDC channel, an error pointer will be > > dereferenced, e.g. on Salvator-XS: > > > > Unable to handle kernel NULL pointer dereference at virtual address 000000000000017d > > ... > > Call trace: > > sysfs_do_create_link_sd.isra.0+0x40/0x108 > > sysfs_create_link+0x20/0x40 > > drm_sysfs_connector_add+0xa8/0xc8 > > drm_connector_register.part.3+0x54/0xb0 > > drm_connector_register_all+0xb0/0xd0 > > drm_modeset_register_all+0x54/0x88 > > drm_dev_register+0x18c/0x1d8 > > rcar_du_probe+0xe4/0x150 > > ... > > > > This happens because vga->ddc either contains a valid DDC channel > > pointer, or -ENODEV, and drm_connector_init_with_ddc() expects a valid > > DDC channel pointer, or NULL. > > > > Fix this by resetting vga->ddc to NULL in case of -ENODEV, and replacing > > the existing error checks by non-NULL checks. > > This is similar to what the HDMI connector driver does. > > > > Fixes: a4f9087e85de141e ("drm/bridge: dumb-vga-dac: Provide ddc symlink in connector sysfs directory") > > Signed-off-by: Geert Uytterhoeven > > --- > > An alternative would be to check if vga->ddc contains an error pointer, > > and calling drm_connector_init() instead of > > drm_connector_init_with_ddc(), like before. > > --- > > drivers/gpu/drm/bridge/dumb-vga-dac.c | 7 ++++--- > > 1 file changed, 4 insertions(+), 3 deletions(-) > > > > diff --git a/drivers/gpu/drm/bridge/dumb-vga-dac.c b/drivers/gpu/drm/bridge/dumb-vga-dac.c > > index 8ef6539ae78a6eb3..7aa789c358829b05 100644 > > --- a/drivers/gpu/drm/bridge/dumb-vga-dac.c > > +++ b/drivers/gpu/drm/bridge/dumb-vga-dac.c > > @@ -42,7 +42,7 @@ static int dumb_vga_get_modes(struct drm_connector *connector) > > struct edid *edid; > > int ret; > > > > - if (IS_ERR(vga->ddc)) > > + if (!vga->ddc) > > goto fallback; > > > > edid = drm_get_edid(connector, vga->ddc); > > @@ -84,7 +84,7 @@ dumb_vga_connector_detect(struct drm_connector *connector, bool force) > > * wire the DDC pins, or the I2C bus might not be working at > > * all. > > */ > > - if (!IS_ERR(vga->ddc) && drm_probe_ddc(vga->ddc)) > > + if (vga->ddc && drm_probe_ddc(vga->ddc)) > > return connector_status_connected; > > > > return connector_status_unknown; > > @@ -197,6 +197,7 @@ static int dumb_vga_probe(struct platform_device *pdev) > > if (PTR_ERR(vga->ddc) == -ENODEV) { > > dev_dbg(&pdev->dev, > > "No i2c bus specified. Disabling EDID readout\n"); > > + vga->ddc = NULL; > > } else { > > dev_err(&pdev->dev, "Couldn't retrieve i2c bus\n"); > > return PTR_ERR(vga->ddc); > > @@ -218,7 +219,7 @@ static int dumb_vga_remove(struct platform_device *pdev) > > > > drm_bridge_remove(&vga->bridge); > > > > - if (!IS_ERR(vga->ddc)) > > + if (vga->ddc) > > i2c_put_adapter(vga->ddc); > > > > return 0; > > > > Looks sane, > > Reviewed-by: Neil Armstrong > > Guenter, can you confirm it also fixes qemu:versatilepb ? > Yes, it does. Tested-by: Guenter Roeck Guenter