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-rw-r--r--kernel/kcmp.c239
1 files changed, 239 insertions, 0 deletions
diff --git a/kernel/kcmp.c b/kernel/kcmp.c
new file mode 100644
index 000000000..5353edfad
--- /dev/null
+++ b/kernel/kcmp.c
@@ -0,0 +1,239 @@
+// 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];
+}
+
+/*
+ * 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);
+}
+
+/* The caller must have pinned the task */
+static struct file *
+get_file_raw_ptr(struct task_struct *task, unsigned int idx)
+{
+ struct file *file;
+
+ rcu_read_lock();
+ file = task_lookup_fd_rcu(task, idx);
+ rcu_read_unlock();
+
+ return file;
+}
+
+static void kcmp_unlock(struct rw_semaphore *l1, struct rw_semaphore *l2)
+{
+ if (likely(l2 != l1))
+ up_read(l2);
+ up_read(l1);
+}
+
+static int kcmp_lock(struct rw_semaphore *l1, struct rw_semaphore *l2)
+{
+ int err;
+
+ if (l2 > l1)
+ swap(l1, l2);
+
+ err = down_read_killable(l1);
+ if (!err && likely(l1 != l2)) {
+ err = down_read_killable_nested(l2, SINGLE_DEPTH_NESTING);
+ if (err)
+ up_read(l1);
+ }
+
+ return err;
+}
+
+#ifdef CONFIG_EPOLL
+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;
+
+ if (copy_from_user(&slot, uslot, sizeof(slot)))
+ return -EFAULT;
+
+ filp = get_file_raw_ptr(task1, idx1);
+ if (!filp)
+ return -EBADF;
+
+ filp_epoll = fget_task(task2, slot.efd);
+ if (!filp_epoll)
+ return -EBADF;
+
+ 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);
+}
+#else
+static int kcmp_epoll_target(struct task_struct *task1,
+ struct task_struct *task2,
+ unsigned long idx1,
+ struct kcmp_epoll_slot __user *uslot)
+{
+ return -EOPNOTSUPP;
+}
+#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->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();
+ 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;
+}
+arch_initcall(kcmp_cookies_init);