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[176.150.251.154]) by smtp.gmail.com with ESMTPSA id 39sm16965wrc.45.2019.08.14.07.46.08 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 14 Aug 2019 07:46:09 -0700 (PDT) Subject: Re: [PATCH] drm/bridge: dumb-vga-dac: Fix dereferencing -ENODEV DDC channel To: Guenter Roeck 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 References: <20190813093046.4976-1-geert+renesas@glider.be> <29ff3bfd-57ee-9c64-3706-555edc8b4675@baylibre.com> <20190814143920.GA30613@roeck-us.net> From: Neil Armstrong Openpgp: preference=signencrypt Autocrypt: addr=narmstrong@baylibre.com; prefer-encrypt=mutual; keydata= mQENBE1ZBs8BCAD78xVLsXPwV/2qQx2FaO/7mhWL0Qodw8UcQJnkrWmgTFRobtTWxuRx8WWP GTjuhvbleoQ5Cxjr+v+1ARGCH46MxFP5DwauzPekwJUD5QKZlaw/bURTLmS2id5wWi3lqVH4 BVF2WzvGyyeV1o4RTCYDnZ9VLLylJ9bneEaIs/7cjCEbipGGFlfIML3sfqnIvMAxIMZrvcl9 qPV2k+KQ7q+aXavU5W+yLNn7QtXUB530Zlk/d2ETgzQ5FLYYnUDAaRl+8JUTjc0CNOTpCeik 80TZcE6f8M76Xa6yU8VcNko94Ck7iB4vj70q76P/J7kt98hklrr85/3NU3oti3nrIHmHABEB AAG0KE5laWwgQXJtc3Ryb25nIDxuYXJtc3Ryb25nQGJheWxpYnJlLmNvbT6JATsEEwEKACUC GyMGCwkIBwMCBhUIAgkKCwQWAgMBAh4BAheABQJXDO2CAhkBAAoJEBaat7Gkz/iubGIH/iyk RqvgB62oKOFlgOTYCMkYpm2aAOZZLf6VKHKc7DoVwuUkjHfIRXdslbrxi4pk5VKU6ZP9AKsN NtMZntB8WrBTtkAZfZbTF7850uwd3eU5cN/7N1Q6g0JQihE7w4GlIkEpQ8vwSg5W7hkx3yQ6 2YzrUZh/b7QThXbNZ7xOeSEms014QXazx8+txR7jrGF3dYxBsCkotO/8DNtZ1R+aUvRfpKg5 ZgABTC0LmAQnuUUf2PHcKFAHZo5KrdO+tyfL+LgTUXIXkK+tenkLsAJ0cagz1EZ5gntuheLD YJuzS4zN+1Asmb9kVKxhjSQOcIh6g2tw7vaYJgL/OzJtZi6JlIW5AQ0ETVkGzwEIALyKDN/O GURaHBVzwjgYq+ZtifvekdrSNl8TIDH8g1xicBYpQTbPn6bbSZbdvfeQPNCcD4/EhXZuhQXM coJsQQQnO4vwVULmPGgtGf8PVc7dxKOeta+qUh6+SRh3vIcAUFHDT3f/Zdspz+e2E0hPV2hi SvICLk11qO6cyJE13zeNFoeY3ggrKY+IzbFomIZY4yG6xI99NIPEVE9lNBXBKIlewIyVlkOa YvJWSV+p5gdJXOvScNN1epm5YHmf9aE2ZjnqZGoMMtsyw18YoX9BqMFInxqYQQ3j/HpVgTSv mo5ea5qQDDUaCsaTf8UeDcwYOtgI8iL4oHcsGtUXoUk33HEAEQEAAYkBHwQYAQIACQUCTVkG zwIbDAAKCRAWmrexpM/4rrXiB/sGbkQ6itMrAIfnM7IbRuiSZS1unlySUVYu3SD6YBYnNi3G 5EpbwfBNuT3H8//rVvtOFK4OD8cRYkxXRQmTvqa33eDIHu/zr1HMKErm+2SD6PO9umRef8V8 2o2oaCLvf4WeIssFjwB0b6a12opuRP7yo3E3gTCSKmbUuLv1CtxKQF+fUV1cVaTPMyT25Od+ RC1K+iOR0F54oUJvJeq7fUzbn/KdlhA8XPGzwGRy4zcsPWvwnXgfe5tk680fEKZVwOZKIEuJ C3v+/yZpQzDvGYJvbyix0lHnrCzq43WefRHI5XTTQbM0WUIBIcGmq38+OgUsMYu4NzLu7uZF Acmp6h8guQINBFYnf6QBEADQ+wBYa+X2n/xIQz/RUoGHf84Jm+yTqRT43t7sO48/cBW9vAn9 GNwnJ3HRJWKATW0ZXrCr40ES/JqM1fUTfiFDB3VMdWpEfwOAT1zXS+0rX8yljgsWR1UvqyEP 3xN0M/40Zk+rdmZKaZS8VQaXbveaiWMEmY7sBV3QvgOzB7UF2It1HwoCon5Y+PvyE3CguhBd 9iq5iEampkMIkbA3FFCpQFI5Ai3BywkLzbA3ZtnMXR8Qt9gFZtyXvFQrB+/6hDzEPnBGZOOx zkd/iIX59SxBuS38LMlhPPycbFNmtauOC0DNpXCv9ACgC9tFw3exER/xQgSpDVc4vrL2Cacr wmQp1k9E0W+9pk/l8S1jcHx03hgCxPtQLOIyEu9iIJb27TjcXNjiInd7Uea195NldIrndD+x 58/yU3X70qVY+eWbqzpdlwF1KRm6uV0ZOQhEhbi0FfKKgsYFgBIBchGqSOBsCbL35f9hK/JC 6LnGDtSHeJs+jd9/qJj4WqF3x8i0sncQ/gszSajdhnWrxraG3b7/9ldMLpKo/OoihfLaCxtv xYmtw8TGhlMaiOxjDrohmY1z7f3rf6njskoIXUO0nabun1nPAiV1dpjleg60s3OmVQeEpr3a K7gR1ljkemJzM9NUoRROPaT7nMlNYQL+IwuthJd6XQqwzp1jRTGG26J97wARAQABiQM+BBgB AgAJBQJWJ3+kAhsCAikJEBaat7Gkz/iuwV0gBBkBAgAGBQJWJ3+kAAoJEHfc29rIyEnRk6MQ AJDo0nxsadLpYB26FALZsWlN74rnFXth5dQVQ7SkipmyFWZhFL8fQ9OiIoxWhM6rSg9+C1w+ n45eByMg2b8H3mmQmyWztdI95OxSREKwbaXVapCcZnv52JRjlc3DoiiHqTZML5x1Z7lQ1T3F 8o9sKrbFO1WQw1+Nc91+MU0MGN0jtfZ0Tvn/ouEZrSXCE4K3oDGtj3AdC764yZVq6CPigCgs 6Ex80k6QlzCdVP3RKsnPO2xQXXPgyJPJlpD8bHHHW7OLfoR9DaBNympfcbQJeekQrTvyoASw EOTPKE6CVWrcQIztUp0WFTdRGgMK0cZB3Xfe6sOp24PQTHAKGtjTHNP/THomkH24Fum9K3iM /4Wh4V2eqGEgpdeSp5K+LdaNyNgaqzMOtt4HYk86LYLSHfFXywdlbGrY9+TqiJ+ZVW4trmui NIJCOku8SYansq34QzYM0x3UFRwff+45zNBEVzctSnremg1mVgrzOfXU8rt+4N1b2MxorPF8 619aCwVP7U16qNSBaqiAJr4e5SNEnoAq18+1Gp8QsFG0ARY8xp+qaKBByWES7lRi3QbqAKZf yOHS6gmYo9gBmuAhc65/VtHMJtxwjpUeN4Bcs9HUpDMDVHdfeRa73wM+wY5potfQ5zkSp0Jp bxnv/cRBH6+c43stTffprd//4Hgz+nJcCgZKtCYIAPkUxABC85ID2CidzbraErVACmRoizhT KR2OiqSLW2x4xdmSiFNcIWkWJB6Qdri0Fzs2dHe8etD1HYaht1ZhZ810s7QOL7JwypO8dscN KTEkyoTGn6cWj0CX+PeP4xp8AR8ot4d0BhtUY34UPzjE1/xyrQFAdnLd0PP4wXxdIUuRs0+n WLY9Aou/vC1LAdlaGsoTVzJ2gX4fkKQIWhX0WVk41BSFeDKQ3RQ2pnuzwedLO94Bf6X0G48O VsbXrP9BZ6snXyHfebPnno/te5XRqZTL9aJOytB/1iUna+1MAwBxGFPvqeEUUyT+gx1l3Acl ZaTUOEkgIor5losDrePdPgE= Organization: Baylibre Message-ID: <591b2c3d-0c12-511a-c044-82459d4b81d0@baylibre.com> Date: Wed, 14 Aug 2019 16:46:01 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 MIME-Version: 1.0 In-Reply-To: <20190814143920.GA30613@roeck-us.net> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 14/08/2019 16:39, Guenter Roeck wrote: > 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 > Thanks for testing, Applying to drm-misc-next