1// SPDX-License-Identifier: GPL-2.0
2/*
3 * Copyright (c) 2020 Francis Laniel <laniel_francis@privacyrequired.com>
4 *
5 * Add tests related to fortified functions in this file.
6 */
7#include "lkdtm.h"
8#include <linux/string.h>
9#include <linux/slab.h>
10
11static volatile int fortify_scratch_space;
12
13static void lkdtm_FORTIFY_STR_OBJECT(void)
14{
15 struct target {
16 char a[10];
17 int foo;
18 } target[3] = {};
19 /*
20 * Using volatile prevents the compiler from determining the value of
21 * 'size' at compile time. Without that, we would get a compile error
22 * rather than a runtime error.
23 */
24 volatile int size = 20;
25
26 pr_info("trying to strcmp() past the end of a struct\n");
27
28 strncpy(p: target[0].a, q: target[1].a, size);
29
30 /* Store result to global to prevent the code from being eliminated */
31 fortify_scratch_space = target[0].a[3];
32
33 pr_err("FAIL: fortify did not block a strncpy() object write overflow!\n");
34 pr_expected_config(CONFIG_FORTIFY_SOURCE);
35}
36
37static void lkdtm_FORTIFY_STR_MEMBER(void)
38{
39 struct target {
40 char a[10];
41 char b[10];
42 } target;
43 volatile int size = 20;
44 char *src;
45
46 src = kmalloc(size, GFP_KERNEL);
47 strscpy(src, "over ten bytes", size);
48 size = strlen(src) + 1;
49
50 pr_info("trying to strncpy() past the end of a struct member...\n");
51
52 /*
53 * strncpy(target.a, src, 20); will hit a compile error because the
54 * compiler knows at build time that target.a < 20 bytes. Use a
55 * volatile to force a runtime error.
56 */
57 strncpy(p: target.a, q: src, size);
58
59 /* Store result to global to prevent the code from being eliminated */
60 fortify_scratch_space = target.a[3];
61
62 pr_err("FAIL: fortify did not block a strncpy() struct member write overflow!\n");
63 pr_expected_config(CONFIG_FORTIFY_SOURCE);
64
65 kfree(objp: src);
66}
67
68static void lkdtm_FORTIFY_MEM_OBJECT(void)
69{
70 int before[10];
71 struct target {
72 char a[10];
73 int foo;
74 } target = {};
75 int after[10];
76 /*
77 * Using volatile prevents the compiler from determining the value of
78 * 'size' at compile time. Without that, we would get a compile error
79 * rather than a runtime error.
80 */
81 volatile int size = 20;
82
83 memset(before, 0, sizeof(before));
84 memset(after, 0, sizeof(after));
85 fortify_scratch_space = before[5];
86 fortify_scratch_space = after[5];
87
88 pr_info("trying to memcpy() past the end of a struct\n");
89
90 pr_info("0: %zu\n", __builtin_object_size(&target, 0));
91 pr_info("1: %zu\n", __builtin_object_size(&target, 1));
92 pr_info("s: %d\n", size);
93 memcpy(&target, &before, size);
94
95 /* Store result to global to prevent the code from being eliminated */
96 fortify_scratch_space = target.a[3];
97
98 pr_err("FAIL: fortify did not block a memcpy() object write overflow!\n");
99 pr_expected_config(CONFIG_FORTIFY_SOURCE);
100}
101
102static void lkdtm_FORTIFY_MEM_MEMBER(void)
103{
104 struct target {
105 char a[10];
106 char b[10];
107 } target;
108 volatile int size = 20;
109 char *src;
110
111 src = kmalloc(size, GFP_KERNEL);
112 strscpy(src, "over ten bytes", size);
113 size = strlen(src) + 1;
114
115 pr_info("trying to memcpy() past the end of a struct member...\n");
116
117 /*
118 * strncpy(target.a, src, 20); will hit a compile error because the
119 * compiler knows at build time that target.a < 20 bytes. Use a
120 * volatile to force a runtime error.
121 */
122 memcpy(target.a, src, size);
123
124 /* Store result to global to prevent the code from being eliminated */
125 fortify_scratch_space = target.a[3];
126
127 pr_err("FAIL: fortify did not block a memcpy() struct member write overflow!\n");
128 pr_expected_config(CONFIG_FORTIFY_SOURCE);
129
130 kfree(objp: src);
131}
132
133/*
134 * Calls fortified strscpy to test that it returns the same result as vanilla
135 * strscpy and generate a panic because there is a write overflow (i.e. src
136 * length is greater than dst length).
137 */
138static void lkdtm_FORTIFY_STRSCPY(void)
139{
140 char *src;
141 char dst[5];
142
143 struct {
144 union {
145 char big[10];
146 char src[5];
147 };
148 } weird = { .big = "hello!" };
149 char weird_dst[sizeof(weird.src) + 1];
150
151 src = kstrdup(s: "foobar", GFP_KERNEL);
152
153 if (src == NULL)
154 return;
155
156 /* Vanilla strscpy returns -E2BIG if size is 0. */
157 if (strscpy(dst, src, 0) != -E2BIG)
158 pr_warn("FAIL: strscpy() of 0 length did not return -E2BIG\n");
159
160 /* Vanilla strscpy returns -E2BIG if src is truncated. */
161 if (strscpy(dst, src, sizeof(dst)) != -E2BIG)
162 pr_warn("FAIL: strscpy() did not return -E2BIG while src is truncated\n");
163
164 /* After above call, dst must contain "foob" because src was truncated. */
165 if (strncmp(dst, "foob", sizeof(dst)) != 0)
166 pr_warn("FAIL: after strscpy() dst does not contain \"foob\" but \"%s\"\n",
167 dst);
168
169 /* Shrink src so the strscpy() below succeeds. */
170 src[3] = '\0';
171
172 /*
173 * Vanilla strscpy returns number of character copied if everything goes
174 * well.
175 */
176 if (strscpy(dst, src, sizeof(dst)) != 3)
177 pr_warn("FAIL: strscpy() did not return 3 while src was copied entirely truncated\n");
178
179 /* After above call, dst must contain "foo" because src was copied. */
180 if (strncmp(dst, "foo", sizeof(dst)) != 0)
181 pr_warn("FAIL: after strscpy() dst does not contain \"foo\" but \"%s\"\n",
182 dst);
183
184 /* Test when src is embedded inside a union. */
185 strscpy(weird_dst, weird.src, sizeof(weird_dst));
186
187 if (strcmp(weird_dst, "hello") != 0)
188 pr_warn("FAIL: after strscpy() weird_dst does not contain \"hello\" but \"%s\"\n",
189 weird_dst);
190
191 /* Restore src to its initial value. */
192 src[3] = 'b';
193
194 /*
195 * Use strlen here so size cannot be known at compile time and there is
196 * a runtime write overflow.
197 */
198 strscpy(dst, src, strlen(src));
199
200 pr_err("FAIL: strscpy() overflow not detected!\n");
201 pr_expected_config(CONFIG_FORTIFY_SOURCE);
202
203 kfree(objp: src);
204}
205
206static struct crashtype crashtypes[] = {
207 CRASHTYPE(FORTIFY_STR_OBJECT),
208 CRASHTYPE(FORTIFY_STR_MEMBER),
209 CRASHTYPE(FORTIFY_MEM_OBJECT),
210 CRASHTYPE(FORTIFY_MEM_MEMBER),
211 CRASHTYPE(FORTIFY_STRSCPY),
212};
213
214struct crashtype_category fortify_crashtypes = {
215 .crashtypes = crashtypes,
216 .len = ARRAY_SIZE(crashtypes),
217};
218

source code of linux/drivers/misc/lkdtm/fortify.c