CVE-2023-53458

media: cx23885: Fix a null-ptr-deref bug in buffer_prepare() and buffer_finish()

In the Linux kernel, the following vulnerability has been resolved: media: cx23885: Fix a null-ptr-deref bug in buffer_prepare() and buffer_finish() When the driver calls cx23885_risc_buffer() to prepare the buffer, the function call dma_alloc_coherent may fail, resulting in a empty buffer risc->cpu. Later when we free the buffer or access the buffer, null ptr deref is triggered. This bug is similar to the following one: https://git.linuxtv.org/media_stage.git/commit/?id=2b064d91440b33fba5b452f2d1b31f13ae911d71. We believe the bug can be also dynamically triggered from user side. Similarly, we fix this by checking the return value of cx23885_risc_buffer() and the value of risc->cpu before buffer free.