capability.c

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/*
 * 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/audit.h>
#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>
#include "cred-internals.h"

#ifndef DDE_LINUX
/*
 * 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);

#ifdef CONFIG_SECURITY_FILE_CAPABILITIES
int file_caps_enabled = 1;

static int __init file_caps_disable(char *str)
{
        file_caps_enabled = 0;
        return 1;
}
__setup("no_file_caps", file_caps_disable);
#endif

/*
 * 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;
}

/*
 * 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;

                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);
        } else
                ret = security_capget(current, pEp, pIp, pPp);

        return ret;
}

/**
 * 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.
 */
SYSCALL_DEFINE2(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 the current process only.  The ability to any other
 * process(es) has been deprecated and removed.
 *
 * The restrictions on setting capabilities are specified as:
 *
 * I: any raised capabilities must be a subset of the old permitted
 * P: any raised capabilities must be a subset of the old permitted
 * E: must be set to a subset of new permitted
 *
 * Returns 0 on success and < 0 on error.
 */
SYSCALL_DEFINE2(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;
        struct cred *new;
        int ret;
        pid_t pid;

        ret = cap_validate_magic(header, &tocopy);
        if (ret != 0)
                return ret;

        if (get_user(pid, &header->pid))
                return -EFAULT;

        /* may only affect current now */
        if (pid != 0 && pid != task_pid_vnr(current))
                return -EPERM;

        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++;
        }

        new = prepare_creds();
        if (!new)
                return -ENOMEM;

        ret = security_capset(new, current_cred(),
                              &effective, &inheritable, &permitted);
        if (ret < 0)
                goto error;

        audit_log_capset(pid, new, current_cred());

        return commit_creds(new);

error:
        abort_creds(new);
        return ret;
}
#endif /* !DDE_LINUX */

/**
 * capable - Determine if the current task has a superior capability in effect
 * @cap: The capability to be tested for
 *
 * Return true if the current task has the given superior capability currently
 * available for use, false if not.
 *
 * This sets PF_SUPERPRIV on the task if the capability is available on the
 * assumption that it's about to be used.
 */
int capable(int cap)
{
        if (unlikely(!cap_valid(cap))) {
                printk(KERN_CRIT "capable() called with invalid cap=%u\n", cap);
                BUG();
        }

        if (security_capable(cap) == 0) {
                current->flags |= PF_SUPERPRIV;
                return 1;
        }
        return 0;
}
EXPORT_SYMBOL(capable);

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