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239 lines
5.4 KiB
239 lines
5.4 KiB
// SPDX-License-Identifier: GPL-2.0 |
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#include <linux/kernel.h> |
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#include <linux/syscalls.h> |
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#include <linux/fdtable.h> |
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#include <linux/string.h> |
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#include <linux/random.h> |
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#include <linux/module.h> |
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#include <linux/ptrace.h> |
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#include <linux/init.h> |
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#include <linux/errno.h> |
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#include <linux/cache.h> |
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#include <linux/bug.h> |
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#include <linux/err.h> |
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#include <linux/kcmp.h> |
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#include <linux/capability.h> |
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#include <linux/list.h> |
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#include <linux/eventpoll.h> |
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#include <linux/file.h> |
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#include <asm/unistd.h> |
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/* |
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* We don't expose the real in-memory order of objects for security reasons. |
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* But still the comparison results should be suitable for sorting. So we |
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* obfuscate kernel pointers values and compare the production instead. |
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* |
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* The obfuscation is done in two steps. First we xor the kernel pointer with |
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* a random value, which puts pointer into a new position in a reordered space. |
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* Secondly we multiply the xor production with a large odd random number to |
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* permute its bits even more (the odd multiplier guarantees that the product |
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* is unique ever after the high bits are truncated, since any odd number is |
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* relative prime to 2^n). |
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* |
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* Note also that the obfuscation itself is invisible to userspace and if needed |
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* it can be changed to an alternate scheme. |
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*/ |
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static unsigned long cookies[KCMP_TYPES][2] __read_mostly; |
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static long kptr_obfuscate(long v, int type) |
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{ |
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return (v ^ cookies[type][0]) * cookies[type][1]; |
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} |
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/* |
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* 0 - equal, i.e. v1 = v2 |
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* 1 - less than, i.e. v1 < v2 |
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* 2 - greater than, i.e. v1 > v2 |
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* 3 - not equal but ordering unavailable (reserved for future) |
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*/ |
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static int kcmp_ptr(void *v1, void *v2, enum kcmp_type type) |
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{ |
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long t1, t2; |
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t1 = kptr_obfuscate((long)v1, type); |
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t2 = kptr_obfuscate((long)v2, type); |
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return (t1 < t2) | ((t1 > t2) << 1); |
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} |
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/* The caller must have pinned the task */ |
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static struct file * |
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get_file_raw_ptr(struct task_struct *task, unsigned int idx) |
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{ |
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struct file *file; |
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rcu_read_lock(); |
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file = task_lookup_fd_rcu(task, idx); |
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rcu_read_unlock(); |
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return file; |
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} |
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static void kcmp_unlock(struct rw_semaphore *l1, struct rw_semaphore *l2) |
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{ |
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if (likely(l2 != l1)) |
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up_read(l2); |
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up_read(l1); |
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} |
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static int kcmp_lock(struct rw_semaphore *l1, struct rw_semaphore *l2) |
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{ |
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int err; |
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if (l2 > l1) |
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swap(l1, l2); |
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err = down_read_killable(l1); |
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if (!err && likely(l1 != l2)) { |
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err = down_read_killable_nested(l2, SINGLE_DEPTH_NESTING); |
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if (err) |
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up_read(l1); |
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} |
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return err; |
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} |
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#ifdef CONFIG_EPOLL |
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static int kcmp_epoll_target(struct task_struct *task1, |
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struct task_struct *task2, |
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unsigned long idx1, |
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struct kcmp_epoll_slot __user *uslot) |
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{ |
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struct file *filp, *filp_epoll, *filp_tgt; |
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struct kcmp_epoll_slot slot; |
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if (copy_from_user(&slot, uslot, sizeof(slot))) |
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return -EFAULT; |
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filp = get_file_raw_ptr(task1, idx1); |
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if (!filp) |
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return -EBADF; |
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filp_epoll = fget_task(task2, slot.efd); |
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if (!filp_epoll) |
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return -EBADF; |
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filp_tgt = get_epoll_tfile_raw_ptr(filp_epoll, slot.tfd, slot.toff); |
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fput(filp_epoll); |
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if (IS_ERR(filp_tgt)) |
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return PTR_ERR(filp_tgt); |
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return kcmp_ptr(filp, filp_tgt, KCMP_FILE); |
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} |
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#else |
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static int kcmp_epoll_target(struct task_struct *task1, |
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struct task_struct *task2, |
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unsigned long idx1, |
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struct kcmp_epoll_slot __user *uslot) |
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{ |
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return -EOPNOTSUPP; |
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} |
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#endif |
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SYSCALL_DEFINE5(kcmp, pid_t, pid1, pid_t, pid2, int, type, |
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unsigned long, idx1, unsigned long, idx2) |
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{ |
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struct task_struct *task1, *task2; |
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int ret; |
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rcu_read_lock(); |
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/* |
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* Tasks are looked up in caller's PID namespace only. |
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*/ |
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task1 = find_task_by_vpid(pid1); |
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task2 = find_task_by_vpid(pid2); |
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if (!task1 || !task2) |
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goto err_no_task; |
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get_task_struct(task1); |
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get_task_struct(task2); |
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rcu_read_unlock(); |
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/* |
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* One should have enough rights to inspect task details. |
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*/ |
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ret = kcmp_lock(&task1->signal->exec_update_lock, |
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&task2->signal->exec_update_lock); |
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if (ret) |
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goto err; |
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if (!ptrace_may_access(task1, PTRACE_MODE_READ_REALCREDS) || |
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!ptrace_may_access(task2, PTRACE_MODE_READ_REALCREDS)) { |
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ret = -EPERM; |
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goto err_unlock; |
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} |
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switch (type) { |
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case KCMP_FILE: { |
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struct file *filp1, *filp2; |
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filp1 = get_file_raw_ptr(task1, idx1); |
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filp2 = get_file_raw_ptr(task2, idx2); |
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if (filp1 && filp2) |
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ret = kcmp_ptr(filp1, filp2, KCMP_FILE); |
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else |
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ret = -EBADF; |
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break; |
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} |
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case KCMP_VM: |
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ret = kcmp_ptr(task1->mm, task2->mm, KCMP_VM); |
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break; |
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case KCMP_FILES: |
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ret = kcmp_ptr(task1->files, task2->files, KCMP_FILES); |
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break; |
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case KCMP_FS: |
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ret = kcmp_ptr(task1->fs, task2->fs, KCMP_FS); |
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break; |
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case KCMP_SIGHAND: |
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ret = kcmp_ptr(task1->sighand, task2->sighand, KCMP_SIGHAND); |
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break; |
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case KCMP_IO: |
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ret = kcmp_ptr(task1->io_context, task2->io_context, KCMP_IO); |
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break; |
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case KCMP_SYSVSEM: |
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#ifdef CONFIG_SYSVIPC |
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ret = kcmp_ptr(task1->sysvsem.undo_list, |
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task2->sysvsem.undo_list, |
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KCMP_SYSVSEM); |
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#else |
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ret = -EOPNOTSUPP; |
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#endif |
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break; |
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case KCMP_EPOLL_TFD: |
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ret = kcmp_epoll_target(task1, task2, idx1, (void *)idx2); |
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break; |
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default: |
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ret = -EINVAL; |
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break; |
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} |
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err_unlock: |
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kcmp_unlock(&task1->signal->exec_update_lock, |
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&task2->signal->exec_update_lock); |
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err: |
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put_task_struct(task1); |
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put_task_struct(task2); |
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return ret; |
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err_no_task: |
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rcu_read_unlock(); |
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return -ESRCH; |
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} |
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static __init int kcmp_cookies_init(void) |
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{ |
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int i; |
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get_random_bytes(cookies, sizeof(cookies)); |
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for (i = 0; i < KCMP_TYPES; i++) |
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cookies[i][1] |= (~(~0UL >> 1) | 1); |
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return 0; |
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} |
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arch_initcall(kcmp_cookies_init);
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