path: root/kernel/sysctl.c

// SPDX-License-Identifier: GPL-2.0-only
/*
 * sysctl.c: General linux system control interface
 */

#include <linux/sysctl.h>
#include <linux/bitmap.h>
#include <linux/proc_fs.h>
#include <linux/ctype.h>
#include <linux/init.h>
#include <linux/kernel.h>
#include <linux/kobject.h>
#include <linux/highuid.h>
#include <linux/writeback.h>
#include <linux/initrd.h>
#include <linux/limits.h>
#include <linux/syscalls.h>
#include <linux/capability.h>

#include "../lib/kstrtox.h"

#include <linux/uaccess.h>
#include <asm/processor.h>

/* shared constants to be used in various sysctls */
const int sysctl_vals[] = { 0, 1, 2, 3, 4, 100, 200, 1000, 3000, INT_MAX, 65535, -1 };
EXPORT_SYMBOL(sysctl_vals);

const unsigned long sysctl_long_vals[] = { 0, 1, LONG_MAX };
EXPORT_SYMBOL_GPL(sysctl_long_vals);

#if defined(CONFIG_SYSCTL)

/* Constants used for minimum and maximum */
static const int ngroups_max = NGROUPS_MAX;
static const int cap_last_cap = CAP_LAST_CAP;

#ifdef CONFIG_PROC_SYSCTL

/**
 * enum sysctl_writes_mode - supported sysctl write modes
 *
 * @SYSCTL_WRITES_LEGACY: each write syscall must fully contain the sysctl value
 *	to be written, and multiple writes on the same sysctl file descriptor
 *	will rewrite the sysctl value, regardless of file position. No warning
 *	is issued when the initial position is not 0.
 * @SYSCTL_WRITES_WARN: same as above but warn when the initial file position is
 *	not 0.
 * @SYSCTL_WRITES_STRICT: writes to numeric sysctl entries must always be at
 *	file position 0 and the value must be fully contained in the buffer
 *	sent to the write syscall. If dealing with strings respect the file
 *	position, but restrict this to the max length of the buffer, anything
 *	passed the max length will be ignored. Multiple writes will append
 *	to the buffer.
 *
 * These write modes control how current file position affects the behavior of
 * updating internal kernel (SYSCTL_USER_TO_KERN) sysctl values through the proc
 * interface on each write.
 */
enum sysctl_writes_mode {
	SYSCTL_WRITES_LEGACY		= -1,
	SYSCTL_WRITES_WARN		= 0,
	SYSCTL_WRITES_STRICT		= 1,
};

static enum sysctl_writes_mode sysctl_writes_strict = SYSCTL_WRITES_STRICT;
#endif /* CONFIG_PROC_SYSCTL */
#endif /* CONFIG_SYSCTL */

/*
 * /proc/sys support
 */

#ifdef CONFIG_PROC_SYSCTL

static int _proc_do_string(char *data, int maxlen, int dir,
		char *buffer, size_t *lenp, loff_t *ppos)
{
	size_t len;
	char c, *p;

	if (!data || !maxlen || !*lenp) {
		*lenp = 0;
		return 0;
	}

	if (SYSCTL_USER_TO_KERN(dir)) {
		if (sysctl_writes_strict == SYSCTL_WRITES_STRICT) {
			/* Only continue writes not past the end of buffer. */
			len = strlen(data);
			if (len > maxlen - 1)
				len = maxlen - 1;

			if (*ppos > len)
				return 0;
			len = *ppos;
		} else {
			/* Start writing from beginning of buffer. */
			len = 0;
		}

		*ppos += *lenp;
		p = buffer;
		while ((p - buffer) < *lenp && len < maxlen - 1) {
			c = *(p++);
			if (c == 0 || c == '\n')
				break;
			data[len++] = c;
		}
		data[len] = 0;
	} else {
		len = strlen(data);
		if</