Kernel UAccess Safety

Rules for exchanging data between a Linux kernel driver and user space without -EFAULT, crashes, or privilege-escalation holes. Load references/uaccess.md before writing any copy_to_user, ioctl, or mmap path.

When to use

• Implementing or reviewing .read / .write / .ioctl / .mmap / .poll / .fasync file operations.
• Copying data across the boundary (copy_to_user, copy_from_user, get_user, put_user, strncpy_from_user, strnlen_user).
• Handling _IO / _IOW / _IOR / _IOWR ioctl commands, including 32-bit compat_ioctl on 64-bit kernels.
• Mapping device memory with remap_pfn_range / pgprot_noncached.
• Debugging -EFAULT, -ENOTTY, or SIGSEGV symptoms in drivers.
• Reviewing patches for CWE-787 / CWE-252 / CWE-190 / CWE-191.

When not to use