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/* ----------------------------------------------------------------------- *
*
* Copyright 2007-2008 H. Peter Anvin - All Rights Reserved
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, Inc., 53 Temple Place Ste 330,
* Boston MA 02111-1307, USA; either version 2 of the License, or
* (at your option) any later version; incorporated herein by reference.
*
* ----------------------------------------------------------------------- */
/*
* setadv.c
*
* (Over)write a data item in the auxilliary data vector. To
* delete an item, set its length to zero.
*
* Return 0 on success, -1 on error, and set errno.
*
*/
#include <string.h>
#include <errno.h>
#include "syslxint.h"
unsigned char syslinux_adv[2*ADV_SIZE];
#define ADV_MAGIC1 0x5a2d2fa5 /* Head signature */
#define ADV_MAGIC2 0xa3041767 /* Total checksum */
#define ADV_MAGIC3 0xdd28bf64 /* Tail signature */
static void cleanup_adv(unsigned char *advbuf)
{
int i;
uint32_t csum;
/* Make sure both copies agree, and update the checksum */
set_32(advbuf, ADV_MAGIC1);
csum = ADV_MAGIC2;
for (i = 8; i < ADV_SIZE-4; i += 4)
csum -= get_32(advbuf+i);
set_32(advbuf+4, csum);
set_32(advbuf+ADV_SIZE-4, ADV_MAGIC3);
memcpy(advbuf+ADV_SIZE, advbuf, ADV_SIZE);
}
int syslinux_setadv(int tag, size_t size, const void *data)
{
uint8_t *p;
size_t left;
uint8_t advtmp[ADV_SIZE];
if ((unsigned)tag-1 > 254) {
errno = EINVAL;
return -1; /* Impossible tag value */
}
if (size > 255) {
errno = ENOSPC; /* Max 255 bytes for a data item */
return -1;
}
left = ADV_LEN;
p = advtmp;
memcpy(p, syslinux_adv+2*4, left); /* Make working copy */
while (left >= 2) {
uint8_t ptag = p[0];
size_t plen = p[1]+2;
if (ptag == ADV_END)
break;
if (ptag == tag) {
/* Found our tag. Delete it. */
if (plen >= left) {
/* Entire remainder is our tag */
break;
}
memmove(p, p+plen, left-plen);
} else {
/* Not our tag */
if (plen > left)
break; /* Corrupt tag (overrun) - overwrite it */
left -= plen;
p += plen;
}
}
/* Now (p, left) reflects the position to write in and how much space
we have for our data. */
if (size) {
if (left < size+2) {
errno = ENOSPC; /* Not enough space for data */
return -1;
}
*p++ = tag;
*p++ = size;
memcpy(p, data, size);
p += size;
left -= size+2;
}
memset(p, 0, left);
/* If we got here, everything went OK, commit the write */
memcpy(syslinux_adv+2*4, advtmp, ADV_LEN);
cleanup_adv(syslinux_adv);
return 0;
}
void syslinux_reset_adv(unsigned char *advbuf)
{
/* Create an all-zero ADV */
memset(advbuf+2*4, 0, ADV_LEN);
cleanup_adv(advbuf);
}
static int adv_consistent(const unsigned char *p)
{
int i;
uint32_t csum;
if (get_32(p) != ADV_MAGIC1 || get_32(p+ADV_SIZE-4) != ADV_MAGIC3)
return 0;
csum = 0;
for (i = 4; i < ADV_SIZE-4; i += 4)
csum += get_32(p+i);
return csum == ADV_MAGIC2;
}
/*
* Verify that an in-memory ADV is consistent, making the copies consistent.
* If neither copy is OK, return -1 and call syslinux_reset_adv().
*/
int syslinux_validate_adv(unsigned char *advbuf)
{
if (adv_consistent(advbuf+0*ADV_SIZE)) {
memcpy(advbuf+ADV_SIZE, advbuf, ADV_SIZE);
return 0;
} else if (adv_consistent(advbuf+1*ADV_SIZE)) {
memcpy(advbuf, advbuf+ADV_SIZE, ADV_SIZE);
return 0;
} else {
syslinux_reset_adv(advbuf);
return -1;
}
}
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