CVE-2023-52492

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

dmaengine: fix NULL pointer in channel unregistration function

_dmaasyncdevicechannelregister() can fail. In case of failure, chan->local is freed (with freepercpu()), and chan->local is nullified. When dmaasyncdeviceunregister() is called (because of managed API or intentionally by DMA controller driver), channels are unconditionally unregistered, leading to this NULL pointer: [ 1.318693] Unable to handle kernel NULL pointer dereference at virtual address 00000000000000d0 [...] [ 1.484499] Call trace: [ 1.486930] devicedel+0x40/0x394 [ 1.490314] deviceunregister+0x20/0x7c [ 1.494220] _dmaasyncdevicechannelunregister+0x68/0xc0

Look at dmaasyncdevice_register() function error path, channel device unregistration is done only if chan->local is not NULL.

Then add the same condition at the beginning of _dmaasyncdevicechannel_unregister() function, to avoid NULL pointer issue whatever the API used to reach this function.