CVE-2021-47276: 
Linux Kernel vulnerability analysis and mitigation

CVE-2021-47276 affects the Linux kernel's ftrace functionality. The vulnerability was discovered when a bug on arm64 caused a bad ip address to be used for updating into a nop in ftrace_init(). While the error path correctly returned -EINVAL instead of -EFAULT due to multiple errors, the ftrace_bug() function attempted to directly read from the invalid ip address location, causing a machine panic (NVD).

The vulnerability occurs in the ftrace_bug() function when it attempts to read directly from an invalid memory address. When ftrace_init() encounters an error and returns -EINVAL, ftrace_bug() tries to report what was at the location of the ip address by reading it directly, without proper validation. This leads to accessing invalid memory addresses, resulting in a system panic (Kernel Commit).

When exploited, this vulnerability causes the machine to panic due to attempting to access invalid memory addresses. This results in a denial of service condition as the system crashes when ftrace encounters certain error conditions (NVD).

The vulnerability is triggered through the ftrace subsystem when it encounters specific error conditions during initialization. It specifically affects arm64 systems when a bad ip address is used for updating into a nop in ftrace_init() (Kernel Commit).

The issue has been fixed by modifying ftrace_bug() to use copy_from_kernel_nofault() to safely access the memory. If the access faults, it reports that the address faulted; otherwise, it reports what was in that location. The fix was implemented in the Linux kernel through commit 6c14133d2d3f (Kernel Commit).