linux/kernel/capability.c
Andrew G. Morgan ab763c7112 security: filesystem capabilities refactor kernel code
To date, we've tried hard to confine filesystem support for capabilities
to the security modules.  This has left a lot of the code in
kernel/capability.c in a state where it looks like it supports something
that filesystem support for capabilities actually suppresses when the LSM
security/commmoncap.c code runs.  What is left is a lot of code that uses
sub-optimal locking in the main kernel

With this change we refactor the main kernel code and make it explicit
which locks are needed and that the only remaining kernel races in this
area are associated with non-filesystem capability code.

Signed-off-by: Andrew G. Morgan <morgan@kernel.org>
Acked-by: Serge Hallyn <serue@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2008-07-24 10:47:22 -07:00

502 lines
13 KiB
C

/*
* linux/kernel/capability.c
*
* Copyright (C) 1997 Andrew Main <zefram@fysh.org>
*
* Integrated into 2.1.97+, Andrew G. Morgan <morgan@kernel.org>
* 30 May 2002: Cleanup, Robert M. Love <rml@tech9.net>
*/
#include <linux/capability.h>
#include <linux/mm.h>
#include <linux/module.h>
#include <linux/security.h>
#include <linux/syscalls.h>
#include <linux/pid_namespace.h>
#include <asm/uaccess.h>
/*
* This lock protects task->cap_* for all tasks including current.
* Locking rule: acquire this prior to tasklist_lock.
*/
static DEFINE_SPINLOCK(task_capability_lock);
/*
* Leveraged for setting/resetting capabilities
*/
const kernel_cap_t __cap_empty_set = CAP_EMPTY_SET;
const kernel_cap_t __cap_full_set = CAP_FULL_SET;
const kernel_cap_t __cap_init_eff_set = CAP_INIT_EFF_SET;
EXPORT_SYMBOL(__cap_empty_set);
EXPORT_SYMBOL(__cap_full_set);
EXPORT_SYMBOL(__cap_init_eff_set);
/*
* More recent versions of libcap are available from:
*
* http://www.kernel.org/pub/linux/libs/security/linux-privs/
*/
static void warn_legacy_capability_use(void)
{
static int warned;
if (!warned) {
char name[sizeof(current->comm)];
printk(KERN_INFO "warning: `%s' uses 32-bit capabilities"
" (legacy support in use)\n",
get_task_comm(name, current));
warned = 1;
}
}
/*
* Version 2 capabilities worked fine, but the linux/capability.h file
* that accompanied their introduction encouraged their use without
* the necessary user-space source code changes. As such, we have
* created a version 3 with equivalent functionality to version 2, but
* with a header change to protect legacy source code from using
* version 2 when it wanted to use version 1. If your system has code
* that trips the following warning, it is using version 2 specific
* capabilities and may be doing so insecurely.
*
* The remedy is to either upgrade your version of libcap (to 2.10+,
* if the application is linked against it), or recompile your
* application with modern kernel headers and this warning will go
* away.
*/
static void warn_deprecated_v2(void)
{
static int warned;
if (!warned) {
char name[sizeof(current->comm)];
printk(KERN_INFO "warning: `%s' uses deprecated v2"
" capabilities in a way that may be insecure.\n",
get_task_comm(name, current));
warned = 1;
}
}
/*
* Version check. Return the number of u32s in each capability flag
* array, or a negative value on error.
*/
static int cap_validate_magic(cap_user_header_t header, unsigned *tocopy)
{
__u32 version;
if (get_user(version, &header->version))
return -EFAULT;
switch (version) {
case _LINUX_CAPABILITY_VERSION_1:
warn_legacy_capability_use();
*tocopy = _LINUX_CAPABILITY_U32S_1;
break;
case _LINUX_CAPABILITY_VERSION_2:
warn_deprecated_v2();
/*
* fall through - v3 is otherwise equivalent to v2.
*/
case _LINUX_CAPABILITY_VERSION_3:
*tocopy = _LINUX_CAPABILITY_U32S_3;
break;
default:
if (put_user((u32)_KERNEL_CAPABILITY_VERSION, &header->version))
return -EFAULT;
return -EINVAL;
}
return 0;
}
#ifndef CONFIG_SECURITY_FILE_CAPABILITIES
/*
* Without filesystem capability support, we nominally support one process
* setting the capabilities of another
*/
static inline int cap_get_target_pid(pid_t pid, kernel_cap_t *pEp,
kernel_cap_t *pIp, kernel_cap_t *pPp)
{
struct task_struct *target;
int ret;
spin_lock(&task_capability_lock);
read_lock(&tasklist_lock);
if (pid && pid != task_pid_vnr(current)) {
target = find_task_by_vpid(pid);
if (!target) {
ret = -ESRCH;
goto out;
}
} else
target = current;
ret = security_capget(target, pEp, pIp, pPp);
out:
read_unlock(&tasklist_lock);
spin_unlock(&task_capability_lock);
return ret;
}
/*
* cap_set_pg - set capabilities for all processes in a given process
* group. We call this holding task_capability_lock and tasklist_lock.
*/
static inline int cap_set_pg(int pgrp_nr, kernel_cap_t *effective,
kernel_cap_t *inheritable,
kernel_cap_t *permitted)
{
struct task_struct *g, *target;
int ret = -EPERM;
int found = 0;
struct pid *pgrp;
spin_lock(&task_capability_lock);
read_lock(&tasklist_lock);
pgrp = find_vpid(pgrp_nr);
do_each_pid_task(pgrp, PIDTYPE_PGID, g) {
target = g;
while_each_thread(g, target) {
if (!security_capset_check(target, effective,
inheritable, permitted)) {
security_capset_set(target, effective,
inheritable, permitted);
ret = 0;
}
found = 1;
}
} while_each_pid_task(pgrp, PIDTYPE_PGID, g);
read_unlock(&tasklist_lock);
spin_unlock(&task_capability_lock);
if (!found)
ret = 0;
return ret;
}
/*
* cap_set_all - set capabilities for all processes other than init
* and self. We call this holding task_capability_lock and tasklist_lock.
*/
static inline int cap_set_all(kernel_cap_t *effective,
kernel_cap_t *inheritable,
kernel_cap_t *permitted)
{
struct task_struct *g, *target;
int ret = -EPERM;
int found = 0;
spin_lock(&task_capability_lock);
read_lock(&tasklist_lock);
do_each_thread(g, target) {
if (target == current
|| is_container_init(target->group_leader))
continue;
found = 1;
if (security_capset_check(target, effective, inheritable,
permitted))
continue;
ret = 0;
security_capset_set(target, effective, inheritable, permitted);
} while_each_thread(g, target);
read_unlock(&tasklist_lock);
spin_unlock(&task_capability_lock);
if (!found)
ret = 0;
return ret;
}
/*
* Given the target pid does not refer to the current process we
* need more elaborate support... (This support is not present when
* filesystem capabilities are configured.)
*/
static inline int do_sys_capset_other_tasks(pid_t pid, kernel_cap_t *effective,
kernel_cap_t *inheritable,
kernel_cap_t *permitted)
{
struct task_struct *target;
int ret;
if (!capable(CAP_SETPCAP))
return -EPERM;
if (pid == -1) /* all procs other than current and init */
return cap_set_all(effective, inheritable, permitted);
else if (pid < 0) /* all procs in process group */
return cap_set_pg(-pid, effective, inheritable, permitted);
/* target != current */
spin_lock(&task_capability_lock);
read_lock(&tasklist_lock);
target = find_task_by_vpid(pid);
if (!target)
ret = -ESRCH;
else {
ret = security_capset_check(target, effective, inheritable,
permitted);
/* having verified that the proposed changes are legal,
we now put them into effect. */
if (!ret)
security_capset_set(target, effective, inheritable,
permitted);
}
read_unlock(&tasklist_lock);
spin_unlock(&task_capability_lock);
return ret;
}
#else /* ie., def CONFIG_SECURITY_FILE_CAPABILITIES */
/*
* If we have configured with filesystem capability support, then the
* only thing that can change the capabilities of the current process
* is the current process. As such, we can't be in this code at the
* same time as we are in the process of setting capabilities in this
* process. The net result is that we can limit our use of locks to
* when we are reading the caps of another process.
*/
static inline int cap_get_target_pid(pid_t pid, kernel_cap_t *pEp,
kernel_cap_t *pIp, kernel_cap_t *pPp)
{
int ret;
if (pid && (pid != task_pid_vnr(current))) {
struct task_struct *target;
spin_lock(&task_capability_lock);
read_lock(&tasklist_lock);
target = find_task_by_vpid(pid);
if (!target)
ret = -ESRCH;
else
ret = security_capget(target, pEp, pIp, pPp);
read_unlock(&tasklist_lock);
spin_unlock(&task_capability_lock);
} else
ret = security_capget(current, pEp, pIp, pPp);
return ret;
}
/*
* With filesystem capability support configured, the kernel does not
* permit the changing of capabilities in one process by another
* process. (CAP_SETPCAP has much less broad semantics when configured
* this way.)
*/
static inline int do_sys_capset_other_tasks(pid_t pid,
kernel_cap_t *effective,
kernel_cap_t *inheritable,
kernel_cap_t *permitted)
{
return -EPERM;
}
#endif /* ie., ndef CONFIG_SECURITY_FILE_CAPABILITIES */
/*
* Atomically modify the effective capabilities returning the original
* value. No permission check is performed here - it is assumed that the
* caller is permitted to set the desired effective capabilities.
*/
kernel_cap_t cap_set_effective(const kernel_cap_t pE_new)
{
kernel_cap_t pE_old;
spin_lock(&task_capability_lock);
pE_old = current->cap_effective;
current->cap_effective = pE_new;
spin_unlock(&task_capability_lock);
return pE_old;
}
EXPORT_SYMBOL(cap_set_effective);
/**
* sys_capget - get the capabilities of a given process.
* @header: pointer to struct that contains capability version and
* target pid data
* @dataptr: pointer to struct that contains the effective, permitted,
* and inheritable capabilities that are returned
*
* Returns 0 on success and < 0 on error.
*/
asmlinkage long sys_capget(cap_user_header_t header, cap_user_data_t dataptr)
{
int ret = 0;
pid_t pid;
unsigned tocopy;
kernel_cap_t pE, pI, pP;
ret = cap_validate_magic(header, &tocopy);
if (ret != 0)
return ret;
if (get_user(pid, &header->pid))
return -EFAULT;
if (pid < 0)
return -EINVAL;
ret = cap_get_target_pid(pid, &pE, &pI, &pP);
if (!ret) {
struct __user_cap_data_struct kdata[_KERNEL_CAPABILITY_U32S];
unsigned i;
for (i = 0; i < tocopy; i++) {
kdata[i].effective = pE.cap[i];
kdata[i].permitted = pP.cap[i];
kdata[i].inheritable = pI.cap[i];
}
/*
* Note, in the case, tocopy < _KERNEL_CAPABILITY_U32S,
* we silently drop the upper capabilities here. This
* has the effect of making older libcap
* implementations implicitly drop upper capability
* bits when they perform a: capget/modify/capset
* sequence.
*
* This behavior is considered fail-safe
* behavior. Upgrading the application to a newer
* version of libcap will enable access to the newer
* capabilities.
*
* An alternative would be to return an error here
* (-ERANGE), but that causes legacy applications to
* unexpectidly fail; the capget/modify/capset aborts
* before modification is attempted and the application
* fails.
*/
if (copy_to_user(dataptr, kdata, tocopy
* sizeof(struct __user_cap_data_struct))) {
return -EFAULT;
}
}
return ret;
}
/**
* sys_capset - set capabilities for a process or (*) a group of processes
* @header: pointer to struct that contains capability version and
* target pid data
* @data: pointer to struct that contains the effective, permitted,
* and inheritable capabilities
*
* Set capabilities for a given process, all processes, or all
* processes in a given process group.
*
* The restrictions on setting capabilities are specified as:
*
* [pid is for the 'target' task. 'current' is the calling task.]
*
* I: any raised capabilities must be a subset of the (old current) permitted
* P: any raised capabilities must be a subset of the (old current) permitted
* E: must be set to a subset of (new target) permitted
*
* Returns 0 on success and < 0 on error.
*/
asmlinkage long sys_capset(cap_user_header_t header, const cap_user_data_t data)
{
struct __user_cap_data_struct kdata[_KERNEL_CAPABILITY_U32S];
unsigned i, tocopy;
kernel_cap_t inheritable, permitted, effective;
int ret;
pid_t pid;
ret = cap_validate_magic(header, &tocopy);
if (ret != 0)
return ret;
if (get_user(pid, &header->pid))
return -EFAULT;
if (copy_from_user(&kdata, data, tocopy
* sizeof(struct __user_cap_data_struct))) {
return -EFAULT;
}
for (i = 0; i < tocopy; i++) {
effective.cap[i] = kdata[i].effective;
permitted.cap[i] = kdata[i].permitted;
inheritable.cap[i] = kdata[i].inheritable;
}
while (i < _KERNEL_CAPABILITY_U32S) {
effective.cap[i] = 0;
permitted.cap[i] = 0;
inheritable.cap[i] = 0;
i++;
}
if (pid && (pid != task_pid_vnr(current)))
ret = do_sys_capset_other_tasks(pid, &effective, &inheritable,
&permitted);
else {
/*
* This lock is required even when filesystem
* capability support is configured - it protects the
* sys_capget() call from returning incorrect data in
* the case that the targeted process is not the
* current one.
*/
spin_lock(&task_capability_lock);
ret = security_capset_check(current, &effective, &inheritable,
&permitted);
/*
* Having verified that the proposed changes are
* legal, we now put them into effect.
*/
if (!ret)
security_capset_set(current, &effective, &inheritable,
&permitted);
spin_unlock(&task_capability_lock);
}
return ret;
}
int __capable(struct task_struct *t, int cap)
{
if (security_capable(t, cap) == 0) {
t->flags |= PF_SUPERPRIV;
return 1;
}
return 0;
}
int capable(int cap)
{
return __capable(current, cap);
}
EXPORT_SYMBOL(capable);