kernel/kcmp.c

File Facts

System

Linux kernel

Corpus path

kernel/kcmp.c

Extension

.c

Size

5507 bytes

Lines

240

Domain

Core OS

Bucket

Scheduler, Processes, Timers, Sync, And Syscalls

Inferred role

Core OS: syscall or user/kernel boundary

Status

core implementation candidate

Why This File Exists

Core operating-system implementation surface: boot, tasks, memory, VFS, syscall-facing interfaces, synchronization, credentials, and isolation.

• Core operating-system implementation surface: boot, tasks, memory, VFS, syscall-facing interfaces, synchronization, credentials, and isolation.
• Defines or participates in a user/kernel boundary; inspect argument validation, copy_from_user/copy_to_user, credentials, and dispatch target.
• Touches user memory; correctness depends on fault-safe copying and privilege boundary handling.
• Uses kernel synchronization; read lock ordering, sleepability, and interrupt context assumptions before translating.
• Defines or uses C structs; map object ownership, embedded links, reference counts, and lock ownership.

Dependency Surface

• linux/kernel.h
• linux/syscalls.h
• linux/fdtable.h
• linux/string.h
• linux/random.h
• linux/module.h
• linux/ptrace.h
• linux/init.h
• linux/errno.h
• linux/cache.h
• linux/bug.h
• linux/err.h
• linux/kcmp.h
• linux/capability.h
• linux/list.h
• linux/eventpoll.h
• linux/file.h
• asm/unistd.h

Detected Declarations

• syscall kcmp
• function kptr_obfuscate
• function kcmp_ptr
• function get_file_raw_ptr
• function kcmp_unlock
• function kcmp_lock
• function kcmp_epoll_target
• function kcmp_epoll_target
• function kcmp_cookies_init

Annotated Snippet

SYSCALL_DEFINE5(kcmp, pid_t, pid1, pid_t, pid2, int, type,
		unsigned long, idx1, unsigned long, idx2)
{
	struct task_struct *task1, *task2;
	int ret;

	rcu_read_lock();

	/*
	 * Tasks are looked up in caller's PID namespace only.
	 */
	task1 = find_task_by_vpid(pid1);
	task2 = find_task_by_vpid(pid2);
	if (unlikely(!task1 || !task2))
		goto err_no_task;

	get_task_struct(task1);
	get_task_struct(task2);

	rcu_read_unlock();

	/*
	 * One should have enough rights to inspect task details.
	 */
	ret = kcmp_lock(&task1->signal->exec_update_lock,
			&task2->signal->exec_update_lock);
	if (ret)
		goto err;
	if (!ptrace_may_access(task1, PTRACE_MODE_READ_REALCREDS) ||
	    !ptrace_may_access(task2, PTRACE_MODE_READ_REALCREDS)) {
		ret = -EPERM;
		goto err_unlock;
	}

	switch (type) {
	case KCMP_FILE: {
		struct file *filp1, *filp2;

		filp1 = get_file_raw_ptr(task1, idx1);
		filp2 = get_file_raw_ptr(task2, idx2);

		if (filp1 && filp2)
			ret = kcmp_ptr(filp1, filp2, KCMP_FILE);
		else
			ret = -EBADF;
		break;
	}
	case KCMP_VM:
		ret = kcmp_ptr(task1->mm, task2->mm, KCMP_VM);
		break;
	case KCMP_FILES:
		ret = kcmp_ptr(task1->files, task2->files, KCMP_FILES);
		break;
	case KCMP_FS:
		ret = kcmp_ptr(task1->fs, task2->fs, KCMP_FS);
		break;
	case KCMP_SIGHAND:
		ret = kcmp_ptr(task1->sighand, task2->sighand, KCMP_SIGHAND);
		break;
	case KCMP_IO:
		ret = kcmp_ptr(task1->io_context, task2->io_context, KCMP_IO);
		break;
	case KCMP_SYSVSEM:
#ifdef CONFIG_SYSVIPC
		ret = kcmp_ptr(task1->sysvsem.undo_list,
			       task2->sysvsem.undo_list,
			       KCMP_SYSVSEM);
#else
		ret = -EOPNOTSUPP;
#endif
		break;
	case KCMP_EPOLL_TFD:
		ret = kcmp_epoll_target(task1, task2, idx1, (void *)idx2);
		break;
	default:
		ret = -EINVAL;
		break;
	}

err_unlock:
	kcmp_unlock(&task1->signal->exec_update_lock,
		    &task2->signal->exec_update_lock);
err:
	put_task_struct(task1);
	put_task_struct(task2);

	return ret;

err_no_task:
	rcu_read_unlock();

Annotation

• Immediate include surface: `linux/kernel.h`, `linux/syscalls.h`, `linux/fdtable.h`, `linux/string.h`, `linux/random.h`, `linux/module.h`, `linux/ptrace.h`, `linux/init.h`.
• Detected declarations: `syscall kcmp`, `function kptr_obfuscate`, `function kcmp_ptr`, `function get_file_raw_ptr`, `function kcmp_unlock`, `function kcmp_lock`, `function kcmp_epoll_target`, `function kcmp_epoll_target`, `function kcmp_cookies_init`.
• Atlas domain: Core OS / Scheduler, Processes, Timers, Sync, And Syscalls.
• Implementation status: core implementation candidate.
• This snippet crosses the user/kernel memory boundary; validate fault handling and access checks before translating the pattern.
• Synchronization appears in or near this file; preserve lock ordering, sleepability, and interrupt-context constraints.

Implementation Notes

• This generated page is the file-by-file coverage layer; curated subsystem chapters should link here when they synthesize a multi-file control flow.
• Core OS pages should be promoted from atlas-only to deep-reviewed when they explain data structures, invariants, locking, lifecycle, and C implementation snippets.
• Driver-family pages are intentionally pattern-oriented unless they are part of the selected PCIe/NVMe representative device path.