cregit-Linux how code gets into the kernel

Release 4.15 kernel/kcmp.c

Directory: kernel
// SPDX-License-Identifier: GPL-2.0
#include <linux/kernel.h>
#include <linux/syscalls.h>
#include <linux/fdtable.h>
#include <linux/string.h>
#include <linux/random.h>
#include <linux/module.h>
#include <linux/ptrace.h>
#include <linux/init.h>
#include <linux/errno.h>
#include <linux/cache.h>
#include <linux/bug.h>
#include <linux/err.h>
#include <linux/kcmp.h>
#include <linux/capability.h>
#include <linux/list.h>
#include <linux/eventpoll.h>
#include <linux/file.h>

#include <asm/unistd.h>

 * We don't expose the real in-memory order of objects for security reasons.
 * But still the comparison results should be suitable for sorting. So we
 * obfuscate kernel pointers values and compare the production instead.
 * The obfuscation is done in two steps. First we xor the kernel pointer with
 * a random value, which puts pointer into a new position in a reordered space.
 * Secondly we multiply the xor production with a large odd random number to
 * permute its bits even more (the odd multiplier guarantees that the product
 * is unique ever after the high bits are truncated, since any odd number is
 * relative prime to 2^n).
 * Note also that the obfuscation itself is invisible to userspace and if needed
 * it can be changed to an alternate scheme.

static unsigned long cookies[KCMP_TYPES][2] __read_mostly;

static long kptr_obfuscate(long v, int type) { return (v ^ cookies[type][0]) * cookies[type][1]; }


Cyrill V. Gorcunov33100.00%1100.00%

/* * 0 - equal, i.e. v1 = v2 * 1 - less than, i.e. v1 < v2 * 2 - greater than, i.e. v1 > v2 * 3 - not equal but ordering unavailable (reserved for future) */
static int kcmp_ptr(void *v1, void *v2, enum kcmp_type type) { long t1, t2; t1 = kptr_obfuscate((long)v1, type); t2 = kptr_obfuscate((long)v2, type); return (t1 < t2) | ((t1 > t2) << 1); }


Cyrill V. Gorcunov5382.81%150.00%
Rasmus Villemoes1117.19%150.00%

/* The caller must have pinned the task */
static struct file * get_file_raw_ptr(struct task_struct *task, unsigned int idx) { struct file *file = NULL; task_lock(task); rcu_read_lock(); if (task->files) file = fcheck_files(task->files, idx); rcu_read_unlock(); task_unlock(task); return file; }


Cyrill V. Gorcunov60100.00%1100.00%

static void kcmp_unlock(struct mutex *m1, struct mutex *m2) { if (likely(m2 != m1)) mutex_unlock(m2); mutex_unlock(m1); }


Cyrill V. Gorcunov35100.00%1100.00%

static int kcmp_lock(struct mutex *m1, struct mutex *m2) { int err; if (m2 > m1) swap(m1, m2); err = mutex_lock_killable(m1); if (!err && likely(m1 != m2)) { err = mutex_lock_killable_nested(m2, SINGLE_DEPTH_NESTING); if (err) mutex_unlock(m1); } return err; }


Cyrill V. Gorcunov74100.00%1100.00%

static int kcmp_epoll_target(struct task_struct *task1, struct task_struct *task2, unsigned long idx1, struct kcmp_epoll_slot __user *uslot) { struct file *filp, *filp_epoll, *filp_tgt; struct kcmp_epoll_slot slot; struct files_struct *files; if (copy_from_user(&slot, uslot, sizeof(slot))) return -EFAULT; filp = get_file_raw_ptr(task1, idx1); if (!filp) return -EBADF; files = get_files_struct(task2); if (!files) return -EBADF; spin_lock(&files->file_lock); filp_epoll = fcheck_files(files, slot.efd); if (filp_epoll) get_file(filp_epoll); else filp_tgt = ERR_PTR(-EBADF); spin_unlock(&files->file_lock); put_files_struct(files); if (filp_epoll) { filp_tgt = get_epoll_tfile_raw_ptr(filp_epoll, slot.tfd, slot.toff); fput(filp_epoll); } if (IS_ERR(filp_tgt)) return PTR_ERR(filp_tgt); return kcmp_ptr(filp, filp_tgt, KCMP_FILE); }


Cyrill V. Gorcunov198100.00%1100.00%

static int kcmp_epoll_target(struct task_struct *task1, struct task_struct *task2, unsigned long idx1, struct kcmp_epoll_slot __user *uslot) { return -EOPNOTSUPP; }


Cyrill V. Gorcunov30100.00%1100.00%

#endif 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 (!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->cred_guard_mutex, &task2->signal->cred_guard_mutex); 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->cred_guard_mutex, &task2->signal->cred_guard_mutex); err: put_task_struct(task1); put_task_struct(task2); return ret; err_no_task: rcu_read_unlock(); return -ESRCH; }
static __init int kcmp_cookies_init(void) { int i; get_random_bytes(cookies, sizeof(cookies)); for (i = 0; i < KCMP_TYPES; i++) cookies[i][1] |= (~(~0UL >> 1) | 1); return 0; }


Cyrill V. Gorcunov58100.00%1100.00%


Overall Contributors

Cyrill V. Gorcunov101698.64%350.00%
Rasmus Villemoes111.07%116.67%
Jann Horn20.19%116.67%
Greg Kroah-Hartman10.10%116.67%
Directory: kernel
Information contained on this website is for historical information purposes only and does not indicate or represent copyright ownership.
Created with cregit.