Revision 98bda63e20daab95bdc084ce00459a4f622a0505 authored by Roman Kiryanov on 19 February 2020, 21:40:06 UTC, committed by David S. Miller on 20 February 2020, 23:02:02 UTC
The description says 'If unsure, say N.' but the module is built as M by default (once the dependencies are satisfied). When the module is selected (Y or M), it enables NETFILTER_FAMILY_BRIDGE and SKB_EXTENSIONS which alter kernel internal structures. We (Android Studio Emulator) currently do not use this module and think this it is more consistent to have it disabled by default as opposite to disabling it explicitly to prevent enabling NETFILTER_FAMILY_BRIDGE and SKB_EXTENSIONS. Signed-off-by: Roman Kiryanov <rkir@google.com> Acked-by: Florian Westphal <fw@strlen.de> Signed-off-by: David S. Miller <davem@davemloft.net>
1 parent ac2fcfa
kcmp.c
// 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 = NULL;
task_lock(task);
rcu_read_lock();
if (task->files)
file = fcheck_files(task->files, idx);
rcu_read_unlock();
task_unlock(task);
return file;
}
static void kcmp_unlock(struct mutex *m1, struct mutex *m2)
{
if (likely(m2 != m1))
mutex_unlock(m2);
mutex_unlock(m1);
}
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;
}
#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;
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);
}
#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->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;
}
arch_initcall(kcmp_cookies_init);
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