1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
|
/*
* Part of Very Secure FTPd
* Licence: GPL v2
* Author: Chris Evans
* secbuf.c
*
* Here are some routines providing the (possibly silly) concept of a secure
* buffer. A secure buffer may not be overflowed. A single byte overflow
* will cause the program to safely terminate.
*/
#include "secbuf.h"
#include "utility.h"
#include "sysutil.h"
#include "sysdeputil.h"
void
vsf_secbuf_alloc(char** p_ptr, unsigned int size)
{
unsigned int page_offset;
unsigned int round_up;
char* p_mmap;
char* p_no_access_page;
unsigned int page_size = vsf_sysutil_getpagesize();
/* Free any previous buffer */
vsf_secbuf_free(p_ptr);
/* Round up to next page size */
page_offset = size % page_size;
if (page_offset)
{
unsigned int num_pages = size / page_size;
num_pages++;
round_up = num_pages * page_size;
}
else
{
/* Allocation is on a page-size boundary */
round_up = size;
}
/* Add on another two pages to make inaccessible */
round_up += page_size * 2;
p_mmap = vsf_sysutil_map_anon_pages(round_up);
/* Map the first and last page inaccessible */
p_no_access_page = p_mmap + round_up - page_size;
vsf_sysutil_memprotect(p_no_access_page, page_size, kVSFSysUtilMapProtNone);
/* Before we make the "before" page inaccessible, store the size in it.
* A little hack so that we don't need to explicitly be passed the size
* when freeing an existing secure buffer
*/
*((unsigned int*)p_mmap) = round_up;
p_no_access_page = p_mmap;
vsf_sysutil_memprotect(p_no_access_page, page_size, kVSFSysUtilMapProtNone);
p_mmap += page_size;
if (page_offset)
{
p_mmap += (page_size - page_offset);
}
*p_ptr = p_mmap;
}
void
vsf_secbuf_free(char** p_ptr)
{
unsigned int map_size;
unsigned long page_offset;
char* p_mmap = *p_ptr;
unsigned int page_size = vsf_sysutil_getpagesize();
if (p_mmap == 0)
{
return;
}
/* Calculate the actual start of the mmap region */
page_offset = (unsigned long) p_mmap % page_size;
if (page_offset)
{
p_mmap -= page_offset;
}
p_mmap -= page_size;
/* First make the first page readable so we can get the size */
vsf_sysutil_memprotect(p_mmap, page_size, kVSFSysUtilMapProtReadOnly);
/* Extract the mapping size */
map_size = *((unsigned int*)p_mmap);
/* Lose the mapping */
vsf_sysutil_memunmap(p_mmap, map_size);
}
|