[SRU][J][PATCH 1/1] drm/bridge: sii902x: Fix probing race issue

[Hui Wang]

From: Tomi Valkeinen <tomi.valkeinen at ideasonboard.com>

A null pointer dereference crash has been observed rarely on TI
platforms using sii9022 bridge:

[   53.271356]  sii902x_get_edid+0x34/0x70 [sii902x]
[   53.276066]  sii902x_bridge_get_edid+0x14/0x20 [sii902x]
[   53.281381]  drm_bridge_get_edid+0x20/0x34 [drm]
[   53.286305]  drm_bridge_connector_get_modes+0x8c/0xcc [drm_kms_helper]
[   53.292955]  drm_helper_probe_single_connector_modes+0x190/0x538 [drm_kms_helper]
[   53.300510]  drm_client_modeset_probe+0x1f0/0xbd4 [drm]
[   53.305958]  __drm_fb_helper_initial_config_and_unlock+0x50/0x510 [drm_kms_helper]
[   53.313611]  drm_fb_helper_initial_config+0x48/0x58 [drm_kms_helper]
[   53.320039]  drm_fbdev_dma_client_hotplug+0x84/0xd4 [drm_dma_helper]
[   53.326401]  drm_client_register+0x5c/0xa0 [drm]
[   53.331216]  drm_fbdev_dma_setup+0xc8/0x13c [drm_dma_helper]
[   53.336881]  tidss_probe+0x128/0x264 [tidss]
[   53.341174]  platform_probe+0x68/0xc4
[   53.344841]  really_probe+0x188/0x3c4
[   53.348501]  __driver_probe_device+0x7c/0x16c
[   53.352854]  driver_probe_device+0x3c/0x10c
[   53.357033]  __device_attach_driver+0xbc/0x158
[   53.361472]  bus_for_each_drv+0x88/0xe8
[   53.365303]  __device_attach+0xa0/0x1b4
[   53.369135]  device_initial_probe+0x14/0x20
[   53.373314]  bus_probe_device+0xb0/0xb4
[   53.377145]  deferred_probe_work_func+0xcc/0x124
[   53.381757]  process_one_work+0x1f0/0x518
[   53.385770]  worker_thread+0x1e8/0x3dc
[   53.389519]  kthread+0x11c/0x120
[   53.392750]  ret_from_fork+0x10/0x20

The issue here is as follows:

- tidss probes, but is deferred as sii902x is still missing.
- sii902x starts probing and enters sii902x_init().
- sii902x calls drm_bridge_add(). Now the sii902x bridge is ready from
  DRM's perspective.
- sii902x calls sii902x_audio_codec_init() and
  platform_device_register_data()
- The registration of the audio platform device causes probing of the
  deferred devices.
- tidss probes, which eventually causes sii902x_bridge_get_edid() to be
  called.
- sii902x_bridge_get_edid() tries to use the i2c to read the edid.
  However, the sii902x driver has not set up the i2c part yet, leading
  to the crash.

Fix this by moving the drm_bridge_add() to the end of the
sii902x_init(), which is also at the very end of sii902x_probe().

Signed-off-by: Tomi Valkeinen <tomi.valkeinen at ideasonboard.com>
Fixes: 21d808405fe4 ("drm/bridge/sii902x: Fix EDID readback")
Acked-by: Linus Walleij <linus.walleij at linaro.org>
Link: https://lore.kernel.org/r/20240103-si902x-fixes-v1-1-b9fd3e448411@ideasonboard.com
Signed-off-by: Neil Armstrong <neil.armstrong at linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20240103-si902x-fixes-v1-1-b9fd3e448411@ideasonboard.com
(backported from commit 08ac6f132dd77e40f786d8af51140c96c6d739c9)
[hui: This backporting moves bridge_add() behind the add_adapter()
and del_adapter() behind the bridge_remove() as the original patch
does, in the meantime, adjust the context due to missing:
f4319f72a9bc ("drm/bridge: sii902x: add support for DRM_BRIDGE_ATTACH_NO_CONNECTOR")
ed5c2f5fd10d ("i2c: Make remove callback return void")
ff1eae1201a4 ("drm/bridge: sii902x: Use devm_regulator_bulk_get_enable()")]
CVE-2024-26607
Signed-off-by: Hui Wang <hui.wang at canonical.com>
---
 drivers/gpu/drm/bridge/sii902x.c | 19 +++++++++++--------
 1 file changed, 11 insertions(+), 8 deletions(-)

diff --git a/drivers/gpu/drm/bridge/sii902x.c b/drivers/gpu/drm/bridge/sii902x.c
index 89558e5815303..66d5bed9a50c2 100644
--- a/drivers/gpu/drm/bridge/sii902x.c
+++ b/drivers/gpu/drm/bridge/sii902x.c
@@ -998,11 +998,6 @@ static int sii902x_init(struct sii902x *sii902x)
 			return ret;
 	}
 
-	sii902x->bridge.funcs = &sii902x_bridge_funcs;
-	sii902x->bridge.of_node = dev->of_node;
-	sii902x->bridge.timings = &default_sii902x_timings;
-	drm_bridge_add(&sii902x->bridge);
-
 	sii902x_audio_codec_init(sii902x, dev);
 
 	i2c_set_clientdata(sii902x->i2c, sii902x);
@@ -1015,7 +1010,16 @@ static int sii902x_init(struct sii902x *sii902x)
 		return -ENOMEM;
 
 	sii902x->i2cmux->priv = sii902x;
-	return i2c_mux_add_adapter(sii902x->i2cmux, 0, 0, 0);
+	ret = i2c_mux_add_adapter(sii902x->i2cmux, 0, 0, 0);
+	if (ret)
+		return ret;
+
+	sii902x->bridge.funcs = &sii902x_bridge_funcs;
+	sii902x->bridge.of_node = dev->of_node;
+	sii902x->bridge.timings = &default_sii902x_timings;
+	drm_bridge_add(&sii902x->bridge);
+
+	return 0;
 }
 
 static int sii902x_probe(struct i2c_client *client,
@@ -1075,12 +1079,11 @@ static int sii902x_probe(struct i2c_client *client,
 }
 
 static int sii902x_remove(struct i2c_client *client)
-
 {
 	struct sii902x *sii902x = i2c_get_clientdata(client);
 
-	i2c_mux_del_adapters(sii902x->i2cmux);
 	drm_bridge_remove(&sii902x->bridge);
+	i2c_mux_del_adapters(sii902x->i2cmux);
 	regulator_bulk_disable(ARRAY_SIZE(sii902x->supplies),
 			       sii902x->supplies);
 
-- 
2.34.1