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Subject[PATCH] drm/bridge: dumb-vga-dac: Fix dereferencing -ENODEV DDC channel
Date
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 <geert+renesas@glider.be>
---
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;
--
2.17.1
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