sys.c

LINUX 1.0 内核c源代码,是一份精简的linux内核源代码

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

#include <linux/config.h>
#include <linux/errno.h>
#include <linux/sched.h>
#include <linux/kernel.h>
#include <linux/times.h>
#include <linux/utsname.h>
#include <linux/param.h>
#include <linux/resource.h>
#include <linux/signal.h>
#include <linux/string.h>
#include <linux/ptrace.h>
#include <linux/stat.h>
#include <linux/mman.h>

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

/*
 * this indicates wether you can reboot with ctrl-alt-del: the default is yes
 */
static int C_A_D = 1;

extern void adjust_clock(void);

#define	PZERO	15

static int proc_sel(struct task_struct *p, int which, int who)
{
	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;
	int error = ESRCH;
	int priority;

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

	if ((priority = PZERO - niceval) <= 0)
		priority = 1;

	for(p = &LAST_TASK; p > &FIRST_TASK; --p) {
		if (!*p || !proc_sel(*p, which, who))
			continue;
		if ((*p)->uid != current->euid &&
			(*p)->uid != current->uid && !suser()) {
			error = EPERM;
			continue;
		}
		if (error == ESRCH)
			error = 0;
		if (priority > (*p)->priority && !suser())
			error = EACCES;
		else
			(*p)->priority = priority;
	}
	return -error;
}

asmlinkage int sys_getpriority(int which, int who)
{
	struct task_struct **p;
	int max_prio = 0;

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

	for(p = &LAST_TASK; p > &FIRST_TASK; --p) {
		if (!*p || !proc_sel(*p, which, who))
			continue;
		if ((*p)->priority > max_prio)
			max_prio = (*p)->priority;
	}
	return(max_prio ? max_prio : -ESRCH);
}

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

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

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

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

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

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

asmlinkage unsigned long save_v86_state(struct vm86_regs * regs)
{
	unsigned long stack;

	if (!current->vm86_info) {
		printk("no vm86_info: BAD\n");
		do_exit(SIGSEGV);
	}
	memcpy_tofs(&(current->vm86_info->regs),regs,sizeof(*regs));
	put_fs_long(current->screen_bitmap,&(current->vm86_info->screen_bitmap));
	stack = current->tss.esp0;
	current->tss.esp0 = current->saved_kernel_stack;
	current->saved_kernel_stack = 0;
	return stack;
}

static void mark_screen_rdonly(struct task_struct * tsk)
{
	unsigned long tmp;
	unsigned long *pg_table;

	if ((tmp = tsk->tss.cr3) != 0) {
		tmp = *(unsigned long *) tmp;
		if (tmp & PAGE_PRESENT) {
			tmp &= PAGE_MASK;
			pg_table = (0xA0000 >> PAGE_SHIFT) + (unsigned long *) tmp;
			tmp = 32;
			while (tmp--) {
				if (PAGE_PRESENT & *pg_table)
					*pg_table &= ~PAGE_RW;
				pg_table++;
			}
		}
	}
}

asmlinkage int sys_vm86(struct vm86_struct * v86)
{
	struct vm86_struct info;
	struct pt_regs * pt_regs = (struct pt_regs *) &v86;

	if (current->saved_kernel_stack)
		return -EPERM;
	memcpy_fromfs(&info,v86,sizeof(info));
/*
 * make sure the vm86() system call doesn't try to do anything silly
 */
	info.regs.__null_ds = 0;
	info.regs.__null_es = 0;
	info.regs.__null_fs = 0;
	info.regs.__null_gs = 0;
/*
 * The eflags register is also special: we cannot trust that the user
 * has set it up safely, so this makes sure interrupt etc flags are
 * inherited from protected mode.
 */
	info.regs.eflags &= 0x00000dd5;
	info.regs.eflags |= ~0x00000dd5 & pt_regs->eflags;
	info.regs.eflags |= VM_MASK;
	current->saved_kernel_stack = current->tss.esp0;
	current->tss.esp0 = (unsigned long) pt_regs;
	current->vm86_info = v86;
	current->screen_bitmap = info.screen_bitmap;
	if (info.flags & VM86_SCREEN_BITMAP)
		mark_screen_rdonly(current);
	__asm__ __volatile__("movl %0,%%esp\n\t"
		"pushl $ret_from_sys_call\n\t"
		"ret"
		: /* no outputs */
		:"g" ((long) &(info.regs)),"a" (info.regs.eax));
	return 0;
}

extern void hard_reset_now(void);

/*
 * 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 magic, int magic_too, int flag)
{
	if (!suser())
		return -EPERM;
	if (magic != 0xfee1dead || magic_too != 672274793)
		return -EINVAL;
	if (flag == 0x01234567)
		hard_reset_now();
	else if (flag == 0x89ABCDEF)
		C_A_D = 1;
	else if (!flag)
		C_A_D = 0;
	else
		return -EINVAL;
	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 wether to reboot at once, or just ignore the ctrl-alt-del.
 */
void ctrl_alt_del(void)
{
	if (C_A_D)
		hard_reset_now();
	else
		send_sig(SIGINT,task[1],1);
}
	

/*
 * This is done BSD-style, with no consideration of the saved gid, except
 * that if you set the effective gid, it sets the saved gid too.  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 w/ Saved ID's. 
 */
asmlinkage int sys_setregid(gid_t rgid, gid_t egid)
{
	int old_rgid = current->gid;

	if (rgid != (gid_t) -1) {
		if ((current->egid==rgid) ||
		    (old_rgid == rgid) || 
		    suser())
			current->gid = rgid;
		else
			return(-EPERM);
	}
	if (egid != (gid_t) -1) {
		if ((old_rgid == egid) ||
		    (current->egid == egid) ||
		    suser()) {
			current->egid = egid;
			current->sgid = egid;
		} else {
			current->gid = old_rgid;
			return(-EPERM);
		}
	}
	return 0;
}

/*
 * setgid() is implemeneted like SysV w/ SAVED_IDS 
 */
asmlinkage int sys_setgid(gid_t gid)
{
	if (suser())
		current->gid = current->egid = current->sgid = gid;
	else if ((gid == current->gid) || (gid == current->sgid))
		current->egid = gid;
	else
		return -EPERM;
	return 0;
}

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

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

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

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

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

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

/*
 * Unprivileged users may change the real user id to the effective uid
 * or vice versa.  (BSD-style)
 *
 * When you set the effective uid, it sets the saved uid too.  This 
 * makes it possible for a setuid 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 setreuid() will be
 * 100% compatible with BSD.  A program which uses just setuid() will be
 * 100% compatible with POSIX w/ Saved ID's. 
 */
asmlinkage int sys_setreuid(uid_t ruid, uid_t euid)
{
	int old_ruid = current->uid;
	
	if (ruid != (uid_t) -1) {
		if ((current->euid==ruid) ||
		    (old_ruid == ruid) ||
		    suser())
			current->uid = ruid;
		else
			return(-EPERM);
	}
	if (euid != (uid_t) -1) {
		if ((old_ruid == euid) ||
		    (current->euid == euid) ||
		    suser()) {
			current->euid = euid;
			current->suid = euid;
		} else {
			current->uid = old_ruid;
			return(-EPERM);
		}
	}
	return 0;
}

/*
 * setuid() is implemeneted like SysV w/ SAVED_IDS 
 * 
 * Note that SAVED_ID's is deficient in that a setuid root program
 * like sendmail, for example, cannot set its uid to be a normal 
 * user and then switch back, because if you're root, setuid() sets
 * the saved uid too.  If you don't like this, blame the bright people
 * in the POSIX commmittee and/or USG.  Note that the BSD-style setreuid()
 * will allow a root program to temporarily drop privileges and be able to
 * regain them by swapping the real and effective uid.  
 */
asmlinkage int sys_setuid(uid_t uid)
{
	if (suser())
		current->uid = current->euid = current->suid = uid;
	else if ((uid == current->uid) || (uid == current->suid))
		current->euid = uid;
	else
		return -EPERM;
	return(0);
}

asmlinkage int sys_times(struct tms * tbuf)
{
	if (tbuf) {
		int error = verify_area(VERIFY_WRITE,tbuf,sizeof *tbuf);
		if (error)
			return error;
		put_fs_long(current->utime,(unsigned long *)&tbuf->tms_utime);
		put_fs_long(current->stime,(unsigned long *)&tbuf->tms_stime);