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/times.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 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 write,
		char *buffer, size_t *lenp, loff_t *ppos)
{
	size_t len;
	char c, *p;

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

	if (write) {
		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 (len > maxlen)
			len = maxlen;

		if (*ppos > len) {
			*lenp = 0;
			return 0;
		}

		data += *ppos;
		len  -= *ppos;

		if (len > *lenp)
			len = *lenp;
		if (len)
			memcpy(buffer, data, len);
		if (len < *lenp) {
			buffer[len] = '\n';
			len++;
		}
		*lenp = len;
		*ppos += len;
	}
	return 0;
}

static void warn_sysctl_write(const struct ctl_table *table)
{
	pr_warn_once("%s wrote to %s when file position was not 0!\n"
		"This will not be supported in the future. To silence this\n"
		"warning, set kernel.sysctl_writes_strict = -1\n",
		current->comm, table->procname);
}

/**
 * proc_first_pos_non_zero_ignore - check if first position is allowed
 * @ppos: file position
 * @table: the sysctl table
 *
 * Returns true if the first position is non-zero and the sysctl_writes_strict
 * mode indicates this is not allowed for numeric input types. String proc
 * handlers can ignore the return value.
 */
static bool proc_first_pos_non_zero_ignore(loff_t *ppos,
					   const struct ctl_table *table)
{
	if (!*ppos)
		return false;

	switch (sysctl_writes_strict) {
	case SYSCTL_WRITES_STRICT:
		return true;
	case SYSCTL_WRITES_WARN:
		warn_sysctl_write(table);
		return false;
	default:
		return false;
	}
}

/**
 * proc_dostring - read a string sysctl
 * @table: the sysctl table
 * @write: %TRUE if this is a write to the sysctl file
 * @buffer: the user buffer
 * @lenp: the size of the user buffer
 * @ppos: file position
 *
 * Reads/writes a string from/to the user buffer. If the kernel
 * buffer provided is not large enough to hold the string, the
 * string is truncated. The copied string is %NULL-terminated.
 * If the string is being read by the user process, it is copied
 * and a newline '\n' is added. It is truncated if the buffer is
 * not large enough.
 *
 * Returns 0 on success.
 */
int proc_dostring(const struct ctl_table *table, int write,
		  void *buffer, size_t *lenp, loff_t *ppos)
{
	if (write)
		proc_first_pos_non_zero_ignore(ppos, table);

	return _proc_do_string(table->data, table->maxlen, write, buffer, lenp,
			ppos);
}

static void proc_skip_spaces(char **buf, size_t *size)
{
	while (*size) {
		if (!isspace(**buf))
			break;
		(*size)--;
		(*buf)++;
	}
}

static void proc_skip_char(char **buf, size_t *size, const char v)
{
	while (*size) {
		if (**buf != v)
			break;
		(*size)--;
		(*buf)++;
	}
}

/**
 * strtoul_lenient - parse an ASCII formatted integer from a buffer and only
 *                   fail on overflow
 *
 * @cp: kernel buffer containing the string to parse
 * @endp: pointer to store the trailing characters
 * @base: the base to use
 * @res: where the parsed integer will be stored
 *
 * In case of success 0 is returned and @res will contain the parsed integer,
 * @endp will hold any trailing characters.
 * This function will fail the parse on overflow. If there wasn't an overflow
 * the function will defer the decision what characters count as invalid to the
 * caller.
 */
static int strtoul_lenient(const char *cp, char **endp, unsigned int base,
			   unsigned long *res)
{
	unsigned long long result;
	unsigned int rv;

	cp = _parse_integer_fixup_radix(cp, &base);
	rv = _parse_integer(cp, base, &result);
	if ((rv & KSTRTOX_OVERFLOW) || (result != (unsigned long)result))
		return -ERANGE;

	cp += rv;

	if (endp)
		*endp = (char *)cp;

	*res = (unsigned long)result;
	return 0;
}

#define TMPBUFLEN 22
/**
 * proc_get_long - reads an ASCII formatted integer from a user buffer
 *
 * @buf: a kernel buffer
 * @size: size of the kernel buffer
 * @val: this is where the number will be stored
 * @neg: set to %TRUE if number is negative
 * @perm_tr: a vector which contains the allowed trailers
 * @perm_tr_len: size of the perm_tr vector
 * @tr: pointer to store the trailer character
 *
 * In case of success %0 is returned and @buf and @size are updated with
 * the amount of bytes read. If @tr is non-NULL and a trailing
 * character exists (size is non-zero after returning from this
 * function), @tr is updated with the trailing character.
 */
static int proc_get_long(char **buf, size_t *size,
			  unsigned long *val, bool *neg,
			  const char *perm_tr, unsigned perm_tr_len, char *tr)
{
	char *p, tmp[TMPBUFLEN];
	ssize_t len = *size;

	if (len <= 0)
		return -EINVAL;

	if (len > TMPBUFLEN - 1)
		len = TMPBUFLEN - 1;

	memcpy(tmp, *buf, len);

	tmp[len] = 0;
	p = tmp;
	if (*p == '-' && *size > 1) {
		*neg = true;
		p++;
	} else
		*neg = false;
	if (!isdigit(*p))
		return -EINVAL;

	if (strtoul_lenient(p, &p, 0, val))
		return -EINVAL;

	len = p - tmp;

	/* We don't know if the next char is whitespace thus we may accept
	 * invalid integers (e.g. 1234...a) or two integers instead of one
	 * (e.g. 123...1). So lets not allow such large numbers. */
	if (len == TMPBUFLEN - 1)
		return -EINVAL;

	if (len < *size && perm_tr_len && !memchr(perm_tr, *p, perm_tr_len))
		return -EINVAL;

	if (tr && (len < *size))
		*tr = *p;

	*buf += len;
	*size -= len;

	return 0;
}

/**
 * proc_put_long - converts an integer to a decimal ASCII formatted string
 *
 * @buf: the user buffer
 * @size: th