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
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
|
/* NOTE: this code does not yet work */
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include <unistd.h>
#include <sys/wait.h>
#include <sys/types.h>
#include <sys/ptrace.h>
#include <link.h>
#include <elf.h>
// Much from http://www.phrack.org/issues.html?issue=59&id=8#article
#if defined(__i386__)
#define Elf_Dyn Elf32_Dyn
#define Elf_Ehdr Elf32_Ehdr
#define Elf_Phdr Elf32_Phdr
#define Elf_Sym Elf32_Sym
#define Elf_Word Elf32_Word
#define Elf_Start 0x08048000
#elif defined(__x86_64__)
#define Elf_Dyn Elf64_Dyn
#define Elf_Ehdr Elf64_Ehdr
#define Elf_Phdr Elf64_Phdr
#define Elf_Sym Elf64_Sym
#define Elf_Word Elf64_Word
#define Elf_Start 0x00400000
#else
#error "What elf arch?"
#endif
/*
* search locations of DT_SYMTAB and DT_STRTAB and save them into global
* variables, also save the nchains from hash table.
*/
unsigned long symtab;
unsigned long strtab;
int nchains;
/* attach to pid */
void ptrace_attach(int pid)
{
if ((ptrace(PTRACE_ATTACH, pid, NULL, NULL)) < 0) {
perror("[-] ptrace_attach");
exit(-1);
}
waitpid(pid, NULL, WUNTRACED);
}
/* detach process */
void ptrace_detach(int pid)
{
if (ptrace(PTRACE_DETACH, pid, NULL, NULL) < 0) {
perror("[-] ptrace_detach");
exit(-1);
}
}
/* read data from location addr */
void read_data(int pid, unsigned long addr, void *vptr, int len)
{
int i, count;
long word;
unsigned long *ptr = (unsigned long *)vptr;
count = i = 0;
while (count < len) {
word = ptrace(PTRACE_PEEKTEXT, pid, addr + count, NULL);
count += 4;
ptr[i++] = word;
}
}
/* read string from pid's memory */
char *read_str(int pid, unsigned long addr, int len)
{
char *ret = calloc(32, sizeof(char));
read_data(pid, addr, ret, len);
return ret;
}
/* write data to location addr */
void write_data(int pid, unsigned long addr, void *vptr, int len)
{
int i, count;
long word;
i = count = 0;
while (count < len) {
memcpy(&word, vptr + count, sizeof(word));
word = ptrace(PTRACE_POKETEXT, pid, addr + count, word);
count += 4;
}
}
/* locate link-map in pid's memory */
struct link_map *locate_linkmap(int pid)
{
Elf_Ehdr *ehdr = malloc(sizeof(Elf_Ehdr));
Elf_Phdr *phdr = malloc(sizeof(Elf_Phdr));
Elf_Dyn *dyn = malloc(sizeof(Elf_Dyn));
Elf_Word got;
struct link_map *l = malloc(sizeof(struct link_map));
unsigned long phdr_addr, dyn_addr, map_addr;
/*
* first we check from elf header, mapped at 0x08048000, the offset
* to the program header table from where we try to locate
* PT_DYNAMIC section.
*/
read_data(pid, Elf_Start, ehdr, sizeof(Elf_Ehdr));
phdr_addr = Elf_Start + ehdr->e_phoff;
printf("[+] Program header at %p.\n", (void *)phdr_addr);
read_data(pid, phdr_addr, phdr, sizeof(Elf_Phdr));
while (phdr->p_type != PT_DYNAMIC)
read_data(pid, phdr_addr += sizeof(Elf_Phdr), phdr, sizeof(Elf_Phdr));
/*
* now go through dynamic section until we find address of the GOT
*/
read_data(pid, phdr->p_vaddr, dyn, sizeof(Elf_Dyn));
dyn_addr = phdr->p_vaddr;
while (dyn->d_tag != DT_PLTGOT)
read_data(pid, dyn_addr += sizeof(Elf_Dyn), dyn, sizeof(Elf_Dyn));
got = (Elf_Word)dyn->d_un.d_ptr;
got += 4; /* second GOT entry, remember? */
/*
* now just read first link_map item and return it
*/
read_data(pid, (unsigned long)got, &map_addr, 4);
read_data(pid, map_addr, l, sizeof(struct link_map));
free(phdr);
free(ehdr);
free(dyn);
return l;
}
/* resolve the tables for symbols*/
void resolv_tables(int pid, struct link_map *map)
{
Elf_Dyn *dyn = malloc(sizeof(Elf_Dyn));
unsigned long addr;
addr = (unsigned long)map->l_ld;
read_data(pid, addr, dyn, sizeof(Elf_Dyn));
while (dyn->d_tag) {
switch (dyn->d_tag) {
case DT_HASH:
read_data(pid, dyn->d_un.d_ptr + map->l_addr + 4, &nchains, sizeof(nchains));
break;
case DT_STRTAB:
strtab = dyn->d_un.d_ptr;
break;
case DT_SYMTAB:
symtab = dyn->d_un.d_ptr;
break;
default:
break;
}
addr += sizeof(Elf_Dyn);
read_data(pid, addr, dyn, sizeof(Elf_Dyn));
}
free(dyn);
}
/* find symbol in DT_SYMTAB */
unsigned long find_sym_in_tables(int pid, struct link_map *map, char *sym_name)
{
Elf_Sym *sym = malloc(sizeof(Elf_Sym));
char *str;
int i = 0;
while (i < nchains) {
read_data(pid, symtab + (i * sizeof(Elf_Sym)), sym, sizeof(Elf_Sym));
i++;
if (ELF32_ST_TYPE(sym->st_info) != STT_FUNC)
continue;
/* read symbol name from the string table */
str = read_str(pid, strtab + sym->st_name, 32);
printf("%s\n", str);
/* compare it with our symbol*/
if (strcmp(str, sym_name) == 0) {
printf("[+] Found symbol.\n");
return (map->l_addr + sym->st_value);
}
}
/* no symbol found, return 0 */
return 0;
}
int main(int argc, char *argv[])
{
int child = fork();
if (child) {
wait(NULL);
struct link_map *map = locate_linkmap(child);
printf("[+] Link map located.\n");
resolv_tables(child, map);
char symbol[] = "exit";
unsigned long address = find_sym_in_tables(child, map, symbol);
if (!symbol)
printf("[+] The value of %s is %lx.\n", symbol, address);
else
printf("[-] No such symbol %s.\n", symbol);
ptrace_detach(child);
} else {
ptrace(PTRACE_TRACEME, 0, NULL, NULL);
execl("/bin/su", "su", "not-a-valid-user", NULL);
}
return 0;
}
|
