capability.c

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/*
 * linux/kernel/capability.c
 *
 * Copyright (C) 1997  Andrew Main <[email protected]>
 *
 * Integrated into 2.1.97+,  Andrew G. Morgan <[email protected]>
 * 30 May 2002: Cleanup, Robert M. Love <[email protected]>
 */

#include <linux/audit.h>
#include <linux/capability.h>
#include <linux/mm.h>
#include <linux/export.h>
#include <linux/security.h>
#include <linux/syscalls.h>
#include <linux/pid_namespace.h>
#include <linux/user_namespace.h>
#include <asm/uaccess.h>

/*
 * Leveraged for setting/resetting capabilities
 */

const kernel_cap_t __cap_empty_set = CAP_EMPTY_SET;

EXPORT_SYMBOL(__cap_empty_set);

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);

/*
 * 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;

        rcu_read_lock();

        target = find_task_by_vpid(pid);
        if (!target)
            ret = -ESRCH;
        else
            ret = security_capget(target, pEp, pIp, pPp);

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

    return ret;
}

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 ((dataptr == NULL) || (ret != 0))
        return ((dataptr == NULL) && (ret == -EINVAL)) ? 0 : 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;
}

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, copybytes;
    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;

    copybytes = tocopy * sizeof(struct __user_cap_data_struct);
    if (copybytes > sizeof(kdata))
        return -EFAULT;

    if (copy_from_user(&kdata, data, copybytes))
        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;
}

bool has_ns_capability(struct task_struct *t,
               struct user_namespace *ns, int cap)
{
    int ret;

    rcu_read_lock();
    ret = security_capable(__task_cred(t), ns, cap);
    rcu_read_unlock();

    return (ret == 0);
}

bool has_capability(struct task_struct *t, int cap)
{
    return has_ns_capability(t, &init_user_ns, cap);
}

bool has_ns_capability_noaudit(struct task_struct *t,
                   struct user_namespace *ns, int cap)
{
    int ret;

    rcu_read_lock();
    ret = security_capable_noaudit(__task_cred(t), ns, cap);
    rcu_read_unlock();

    return (ret == 0);
}

bool has_capability_noaudit(struct task_struct *t, int cap)
{
    return has_ns_capability_noaudit(t, &init_user_ns, cap);
}

bool ns_capable(struct user_namespace *ns, int cap)
{
    if (unlikely(!cap_valid(cap))) {
        printk(KERN_CRIT "capable() called with invalid cap=%u\n", cap);
        BUG();
    }

    if (security_capable(current_cred(), ns, cap) == 0) {
        current->flags |= PF_SUPERPRIV;
        return true;
    }
    return false;
}
EXPORT_SYMBOL(ns_capable);

bool capable(int cap)
{
    return ns_capable(&init_user_ns, cap);
}
EXPORT_SYMBOL(capable);

bool nsown_capable(int cap)
{
    return ns_capable(current_user_ns(), cap);
}

bool inode_capable(const struct inode *inode, int cap)
{
    struct user_namespace *ns = current_user_ns();

    return ns_capable(ns, cap) && kuid_has_mapping(ns, inode->i_uid);
}