1 files changed, 217 insertions, 0 deletions
diff --git a/drivers/misc/lkdtm/fortify.c b/drivers/misc/lkdtm/fortify.c
new file mode 100644
index 000000000..015927665
--- /dev/null
+++ b/drivers/misc/lkdtm/fortify.c
@@ -0,0 +1,217 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (c) 2020 Francis Laniel <laniel_francis@privacyrequired.com>
+ *
+ * Add tests related to fortified functions in this file.
+ */
+#include "lkdtm.h"
+#include <linux/string.h>
+#include <linux/slab.h>
+
+static volatile int fortify_scratch_space;
+
+static void lkdtm_FORTIFY_STR_OBJECT(void)
+{
+	struct target {
+		char a[10];
+		int foo;
+	} target[3] = {};
+	/*
+	 * Using volatile prevents the compiler from determining the value of
+	 * 'size' at compile time. Without that, we would get a compile error
+	 * rather than a runtime error.
+	 */
+	volatile int size = 20;
+
+	pr_info("trying to strcmp() past the end of a struct\n");
+
+	strncpy(target[0].a, target[1].a, size);
+
+	/* Store result to global to prevent the code from being eliminated */
+	fortify_scratch_space = target[0].a[3];
+
+	pr_err("FAIL: fortify did not block a strncpy() object write overflow!\n");
+	pr_expected_config(CONFIG_FORTIFY_SOURCE);
+}
+
+static void lkdtm_FORTIFY_STR_MEMBER(void)
+{
+	struct target {
+		char a[10];
+		char b[10];
+	} target;
+	volatile int size = 20;
+	char *src;
+
+	src = kmalloc(size, GFP_KERNEL);
+	strscpy(src, "over ten bytes", size);
+	size = strlen(src) + 1;
+
+	pr_info("trying to strncpy() past the end of a struct member...\n");
+
+	/*
+	 * strncpy(target.a, src, 20); will hit a compile error because the
+	 * compiler knows at build time that target.a < 20 bytes. Use a
+	 * volatile to force a runtime error.
+	 */
+	strncpy(target.a, src, size);
+
+	/* Store result to global to prevent the code from being eliminated */
+	fortify_scratch_space = target.a[3];
+
+	pr_err("FAIL: fortify did not block a strncpy() struct member write overflow!\n");
+	pr_expected_config(CONFIG_FORTIFY_SOURCE);
+
+	kfree(src);
+}
+
+static void lkdtm_FORTIFY_MEM_OBJECT(void)
+{
+	int before[10];
+	struct target {
+		char a[10];
+		int foo;
+	} target = {};
+	int after[10];
+	/*
+	 * Using volatile prevents the compiler from determining the value of
+	 * 'size' at compile time. Without that, we would get a compile error
+	 * rather than a runtime error.
+	 */
+	volatile int size = 20;
+
+	memset(before, 0, sizeof(before));
+	memset(after, 0, sizeof(after));
+	fortify_scratch_space = before[5];
+	fortify_scratch_space = after[5];
+
+	pr_info("trying to memcpy() past the end of a struct\n");
+
+	pr_info("0: %zu\n", __builtin_object_size(&target, 0));
+	pr_info("1: %zu\n", __builtin_object_size(&target, 1));
+	pr_info("s: %d\n", size);
+	memcpy(&target, &before, size);
+
+	/* Store result to global to prevent the code from being eliminated */
+	fortify_scratch_space = target.a[3];
+
+	pr_err("FAIL: fortify did not block a memcpy() object write overflow!\n");
+	pr_expected_config(CONFIG_FORTIFY_SOURCE);
+}
+
+static void lkdtm_FORTIFY_MEM_MEMBER(void)
+{
+	struct target {
+		char a[10];
+		char b[10];
+	} target;
+	volatile int size = 20;
+	char *src;
+
+	src = kmalloc(size, GFP_KERNEL);
+	strscpy(src, "over ten bytes", size);
+	size = strlen(src) + 1;
+
+	pr_info("trying to memcpy() past the end of a struct member...\n");
+
+	/*
+	 * strncpy(target.a, src, 20); will hit a compile error because the
+	 * compiler knows at build time that target.a < 20 bytes. Use a
+	 * volatile to force a runtime error.
+	 */
+	memcpy(target.a, src, size);
+
+	/* Store result to global to prevent the code from being eliminated */
+	fortify_scratch_space = target.a[3];
+
+	pr_err("FAIL: fortify did not block a memcpy() struct member write overflow!\n");
+	pr_expected_config(CONFIG_FORTIFY_SOURCE);
+
+	kfree(src);
+}
+
+/*
+ * Calls fortified strscpy to test that it returns the same result as vanilla
+ * strscpy and generate a panic because there is a write overflow (i.e. src
+ * length is greater than dst length).
+ */
+static void lkdtm_FORTIFY_STRSCPY(void)
+{
+	char *src;
+	char dst[5];
+
+	struct {
+		union {
+			char big[10];
+			char src[5];
+		};
+	} weird = { .big = "hello!" };
+	char weird_dst[sizeof(weird.src) + 1];
+
+	src = kstrdup("foobar", GFP_KERNEL);
+
+	if (src == NULL)
+		return;
+
+	/* Vanilla strscpy returns -E2BIG if size is 0. */
+	if (strscpy(dst, src, 0) != -E2BIG)
+		pr_warn("FAIL: strscpy() of 0 length did not return -E2BIG\n");
+
+	/* Vanilla strscpy returns -E2BIG if src is truncated. */
+	if (strscpy(dst, src, sizeof(dst)) != -E2BIG)
+		pr_warn("FAIL: strscpy() did not return -E2BIG while src is truncated\n");
+
+	/* After above call, dst must contain "foob" because src was truncated. */
+	if (strncmp(dst, "foob", sizeof(dst)) != 0)
+		pr_warn("FAIL: after strscpy() dst does not contain \"foob\" but \"%s\"\n",
+			dst);
+
+	/* Shrink src so the strscpy() below succeeds. */
+	src[3] = '\0';
+
+	/*
+	 * Vanilla strscpy returns number of character copied if everything goes
+	 * well.
+	 */
+	if (strscpy(dst, src, sizeof(dst)) != 3)
+		pr_warn("FAIL: strscpy() did not return 3 while src was copied entirely truncated\n");
+
+	/* After above call, dst must contain "foo" because src was copied. */
+	if (strncmp(dst, "foo", sizeof(dst)) != 0)
+		pr_warn("FAIL: after strscpy() dst does not contain \"foo\" but \"%s\"\n",
+			dst);
+
+	/* Test when src is embedded inside a union. */
+	strscpy(weird_dst, weird.src, sizeof(weird_dst));
+
+	if (strcmp(weird_dst, "hello") != 0)
+		pr_warn("FAIL: after strscpy() weird_dst does not contain \"hello\" but \"%s\"\n",
+			weird_dst);
+
+	/* Restore src to its initial value. */
+	src[3] = 'b';
+
+	/*
+	 * Use strlen here so size cannot be known at compile time and there is
+	 * a runtime write overflow.
+	 */
+	strscpy(dst, src, strlen(src));
+
+	pr_err("FAIL: strscpy() overflow not detected!\n");
+	pr_expected_config(CONFIG_FORTIFY_SOURCE);
+
+	kfree(src);
+}
+
+static struct crashtype crashtypes[] = {
+	CRASHTYPE(FORTIFY_STR_OBJECT),
+	CRASHTYPE(FORTIFY_STR_MEMBER),
+	CRASHTYPE(FORTIFY_MEM_OBJECT),
+	CRASHTYPE(FORTIFY_MEM_MEMBER),
+	CRASHTYPE(FORTIFY_STRSCPY),
+};
+
+struct crashtype_category fortify_crashtypes = {
+	.crashtypes = crashtypes,
+	.len	    = ARRAY_SIZE(crashtypes),
+};