CVE-2024-26607: drm/bridge: sii902x: Fix probing race issue

In the Linux kernel, the following vulnerability has been resolved:

drm/bridge: sii902x: Fix probing race issue

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

[ 53.271356] sii902xgetedid+0x34/0x70 [sii902x] [ 53.276066] sii902xbridgegetedid+0x14/0x20 [sii902x] [ 53.281381] drmbridgegetedid+0x20/0x34 [drm] [ 53.286305] drmbridgeconnectorgetmodes+0x8c/0xcc [drmkmshelper] [ 53.292955] drmhelperprobesingleconnectormodes+0x190/0x538 [drmkmshelper] [ 53.300510] drmclientmodesetprobe+0x1f0/0xbd4 [drm] [ 53.305958] drmfbhelperinitialconfigandunlock+0x50/0x510 [drmkmshelper] [ 53.313611] drmfbhelperinitialconfig+0x48/0x58 [drmkmshelper] [ 53.320039] drmfbdevdmaclienthotplug+0x84/0xd4 [drmdmahelper] [ 53.326401] drmclientregister+0x5c/0xa0 [drm] [ 53.331216] drmfbdevdmasetup+0xc8/0x13c [drmdmahelper] [ 53.336881] tidssprobe+0x128/0x264 [tidss] [ 53.341174] platformprobe+0x68/0xc4 [ 53.344841] reallyprobe+0x188/0x3c4 [ 53.348501] driverprobedevice+0x7c/0x16c [ 53.352854] driverprobedevice+0x3c/0x10c [ 53.357033] deviceattachdriver+0xbc/0x158 [ 53.361472] busforeachdrv+0x88/0xe8 [ 53.365303] deviceattach+0xa0/0x1b4 [ 53.369135] deviceinitialprobe+0x14/0x20 [ 53.373314] busprobedevice+0xb0/0xb4 [ 53.377145] deferredprobeworkfunc+0xcc/0x124 [ 53.381757] processonework+0x1f0/0x518 [ 53.385770] workerthread+0x1e8/0x3dc [ 53.389519] kthread+0x11c/0x120 [ 53.392750] retfromfork+0x10/0x20

The issue here is as follows:

- tidss probes, but is deferred as sii902x is still missing. - sii902x starts probing and enters sii902xinit(). - sii902x calls drmbridgeadd(). Now the sii902x bridge is ready from DRM's perspective. - sii902x calls sii902xaudiocodecinit() and platformdeviceregisterdata() - The registration of the audio platform device causes probing of the deferred devices. - tidss probes, which eventually causes sii902xbridgegetedid() to be called. - sii902xbridgegetedid() 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 drmbridgeadd() to the end of the sii902xinit(), which is also at the very end of sii902xprobe().