> CVE-2021-25491: Kernel NULL Pointer Dereferences due to Missing Error Checks

There are a series of memory corruption vulnerabilities in Samsung Exynos kernels, due to improper error checks, after dma_buf_vmap calls. These bugs can be abused by various privileged processes to cause NULL pointer accesses and crash the kernel. Vulnerability Details The kernel uses the dma_buf_vmap function if it needs to map a dma buffer into the kernel address space to access its content. This function returns a NULL pointer if it encounters an error during its execution. While some drivers employ a null check on the returned pointer, many call sites incorrectly use the IS_ERR macro which explicitly allows NULL pointers.