sys.c

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/*
 *  linux/kernel/sys.c
 *
 *  Copyright (C) 1991, 1992  Linus Torvalds
 */

#include <linux/mm.h>
#include <linux/utsname.h>
#include <linux/mman.h>
#include <linux/smp_lock.h>
#include <linux/notifier.h>
#include <linux/reboot.h>
#include <linux/prctl.h>

#include <asm/uaccess.h>
#include <asm/io.h>

/*
 * this indicates whether you can reboot with ctrl-alt-del: the default is yes
 */

int C_A_D = 1;


/*
 *	Notifier list for kernel code which wants to be called
 *	at shutdown. This is used to stop any idling DMA operations
 *	and the like. 
 */

struct notifier_block *reboot_notifier_list = NULL;

int register_reboot_notifier(struct notifier_block * nb)
{
	return notifier_chain_register(&reboot_notifier_list, nb);
}

int unregister_reboot_notifier(struct notifier_block * nb)
{
	return notifier_chain_unregister(&reboot_notifier_list, nb);
}



extern void adjust_clock(void);

asmlinkage int sys_ni_syscall(void)
{
	return -ENOSYS;
}

static int proc_sel(struct task_struct *p, int which, int who)
{
	if(p->pid)
	{
		switch (which) {
			case PRIO_PROCESS:
				if (!who && p == current)
					return 1;
				return(p->pid == who);
			case PRIO_PGRP:
				if (!who)
					who = current->pgrp;
				return(p->pgrp == who);
			case PRIO_USER:
				if (!who)
					who = current->uid;
				return(p->uid == who);
		}
	}
	return 0;
}

asmlinkage int sys_setpriority(int which, int who, int niceval)
{
	struct task_struct *p;
	unsigned int priority;
	int error;

	if (which > 2 || which < 0)
		return -EINVAL;

	/* normalize: avoid signed division (rounding problems) */
	error = ESRCH;
	priority = niceval;
	if (niceval < 0)
		priority = -niceval;
	if (priority > 20)
		priority = 20;
	priority = (priority * DEF_PRIORITY + 10) / 20 + DEF_PRIORITY;

	if (niceval >= 0) {
		priority = 2*DEF_PRIORITY - priority;
		if (!priority)
			priority = 1;
	}

	read_lock(&tasklist_lock);
	for_each_task(p) {
		if (!proc_sel(p, which, who))
			continue;
		if (p->uid != current->euid &&
			p->uid != current->uid && !capable(CAP_SYS_NICE)) {
			error = EPERM;
			continue;
		}
		if (error == ESRCH)
			error = 0;
		if (priority > p->priority && !capable(CAP_SYS_NICE))
			error = EACCES;
		else
			p->priority = priority;
	}
	read_unlock(&tasklist_lock);

	return -error;
}

/*
 * Ugh. To avoid negative return values, "getpriority()" will
 * not return the normal nice-value, but a value that has been
 * offset by 20 (ie it returns 0..40 instead of -20..20)
 */
asmlinkage int sys_getpriority(int which, int who)
{
	struct task_struct *p;
	long max_prio = -ESRCH;

	if (which > 2 || which < 0)
		return -EINVAL;

	read_lock(&tasklist_lock);
	for_each_task (p) {
		if (!proc_sel(p, which, who))
			continue;
		if (p->priority > max_prio)
			max_prio = p->priority;
	}
	read_unlock(&tasklist_lock);

	/* scale the priority from timeslice to 0..40 */
	if (max_prio > 0)
		max_prio = (max_prio * 20 + DEF_PRIORITY/2) / DEF_PRIORITY;
	return max_prio;
}


/*
 * Reboot system call: for obvious reasons only root may call it,
 * and even root needs to set up some magic numbers in the registers
 * so that some mistake won't make this reboot the whole machine.
 * You can also set the meaning of the ctrl-alt-del-key here.
 *
 * reboot doesn't sync: do that yourself before calling this.
 */
asmlinkage int sys_reboot(int magic1, int magic2, int cmd, void * arg)
{
	char buffer[256];

	/* We only trust the superuser with rebooting the system. */
	if (!capable(CAP_SYS_BOOT))
		return -EPERM;

	/* For safety, we require "magic" arguments. */
	if (magic1 != LINUX_REBOOT_MAGIC1 ||
	    (magic2 != LINUX_REBOOT_MAGIC2 && magic2 != LINUX_REBOOT_MAGIC2A &&
			magic2 != LINUX_REBOOT_MAGIC2B))
		return -EINVAL;

	lock_kernel();
	switch (cmd) {
	case LINUX_REBOOT_CMD_RESTART:
		notifier_call_chain(&reboot_notifier_list, SYS_RESTART, NULL);
		printk(KERN_EMERG "Restarting system.\n");
		machine_restart(NULL);
		break;

	case LINUX_REBOOT_CMD_CAD_ON:
		C_A_D = 1;
		break;

	case LINUX_REBOOT_CMD_CAD_OFF:
		C_A_D = 0;
		break;

	case LINUX_REBOOT_CMD_HALT:
		notifier_call_chain(&reboot_notifier_list, SYS_HALT, NULL);
		printk(KERN_EMERG "System halted.\n");
		machine_halt();
		do_exit(0);
		break;

	case LINUX_REBOOT_CMD_POWER_OFF:
		notifier_call_chain(&reboot_notifier_list, SYS_POWER_OFF, NULL);
		printk(KERN_EMERG "Power down.\n");
		machine_power_off();
		do_exit(0);
		break;

	case LINUX_REBOOT_CMD_RESTART2:
		if (strncpy_from_user(&buffer[0], (char *)arg, sizeof(buffer) - 1) < 0) {
			unlock_kernel();
			return -EFAULT;
		}
		buffer[sizeof(buffer) - 1] = '\0';

		notifier_call_chain(&reboot_notifier_list, SYS_RESTART, buffer);
		printk(KERN_EMERG "Restarting system with command '%s'.\n", buffer);
		machine_restart(buffer);
		break;

	default:
		unlock_kernel();
		return -EINVAL;
		break;
	};
	unlock_kernel();
	return 0;
}

/*
 * This function gets called by ctrl-alt-del - ie the keyboard interrupt.
 * As it's called within an interrupt, it may NOT sync: the only choice
 * is whether to reboot at once, or just ignore the ctrl-alt-del.
 */
void ctrl_alt_del(void)
{
	if (C_A_D) {
		notifier_call_chain(&reboot_notifier_list, SYS_RESTART, NULL);
		machine_restart(NULL);
	} else
		kill_proc(1, SIGINT, 1);
}
	

/*
 * Unprivileged users may change the real gid to the effective gid
 * or vice versa.  (BSD-style)
 *
 * If you set the real gid at all, or set the effective gid to a value not
 * equal to the real gid, then the saved gid is set to the new effective gid.
 *
 * This makes it possible for a setgid program to completely drop its
 * privileges, which is often a useful assertion to make when you are doing
 * a security audit over a program.
 *
 * The general idea is that a program which uses just setregid() will be
 * 100% compatible with BSD.  A program which uses just setgid() will be
 * 100% compatible with POSIX with saved IDs. 
 *
 * SMP: There are not races, the GIDs are checked only by filesystem
 *      operations (as far as semantic preservation is concerned).
 */
asmlinkage int sys_setregid(gid_t rgid, gid_t egid)
{
	int old_rgid = current->gid;
	int old_egid = current->egid;

	if (rgid != (gid_t) -1) {
		if ((old_rgid == rgid) ||
		    (current->egid==rgid) ||
		    capable(CAP_SETGID))
			current->gid = rgid;
		else
			return -EPERM;
	}
	if (egid != (gid_t) -1) {
		if ((old_rgid == egid) ||
		    (current->egid == egid) ||
		    (current->sgid == egid) ||
		    capable(CAP_SETGID))
			current->fsgid = current->egid = egid;
		else {
			current->gid = old_rgid;
			return -EPERM;
		}
	}
	if (rgid != (gid_t) -1 ||
	    (egid != (gid_t) -1 && egid != old_rgid))
		current->sgid = current->egid;
	current->fsgid = current->egid;
	if (current->egid != old_egid)
		current->dumpable = 0;
	return 0;
}

/*
 * setgid() is implemented like SysV w/ SAVED_IDS 
 *
 * SMP: Same implicit races as above.
 */
asmlinkage int sys_setgid(gid_t gid)
{
	int old_egid = current->egid;