Commit 4ce615e7 authored by Kees Cook's avatar Kees Cook
Browse files

fortify: Provide KUnit counters for failure testing 



The standard C string APIs were not designed to have a failure mode;
they were expected to always succeed without memory safety issues.
Normally, CONFIG_FORTIFY_SOURCE will use fortify_panic() to stop
processing, as truncating a read or write may provide an even worse
system state. However, this creates a problem for testing under things
like KUnit, which needs a way to survive failures.

When building with CONFIG_KUNIT, provide a failure path for all users
of fortify_panic, and track whether the failure was a read overflow or
a write overflow, for KUnit tests to examine. Inspired by similar logic
in the slab tests.

Signed-off-by: default avatarKees Cook <keescook@chromium.org>
parent 1a78f8cb

include/linux/fortify-string.h

+23 −20
Original line number Diff line number Diff line
@@ -15,8 +15,10 @@ 
#define FORTIFY_REASON(func, write)	(FIELD_PREP(BIT(0), write) | \

					 FIELD_PREP(GENMASK(7, 1), func))



#define fortify_panic(func, write)	\

#ifndef fortify_panic

# define fortify_panic(func, write, retfail)	\

	 __fortify_panic(FORTIFY_REASON(func, write))

#endif



#define FORTIFY_READ		 0

#define FORTIFY_WRITE		 1
@@ -181,7 +183,7 @@ char *strncpy(char * const POS p, const char *q, __kernel_size_t size) 
	if (__compiletime_lessthan(p_size, size))

		__write_overflow();

	if (p_size < size)

		fortify_panic(FORTIFY_FUNC_strncpy, FORTIFY_WRITE);

		fortify_panic(FORTIFY_FUNC_strncpy, FORTIFY_WRITE, p);

	return __underlying_strncpy(p, q, size);

}
@@ -212,7 +214,7 @@ __FORTIFY_INLINE __kernel_size_t strnlen(const char * const POS p, __kernel_size 
	/* Do not check characters beyond the end of p. */

	ret = __real_strnlen(p, maxlen < p_size ? maxlen : p_size);

	if (p_size <= ret && maxlen != ret)

		fortify_panic(FORTIFY_FUNC_strnlen, FORTIFY_READ);

		fortify_panic(FORTIFY_FUNC_strnlen, FORTIFY_READ, ret);

	return ret;

}
@@ -248,7 +250,7 @@ __kernel_size_t __fortify_strlen(const char * const POS p) 
		return __underlying_strlen(p);

	ret = strnlen(p, p_size);

	if (p_size <= ret)

		fortify_panic(FORTIFY_FUNC_strlen, FORTIFY_READ);

		fortify_panic(FORTIFY_FUNC_strlen, FORTIFY_READ, ret);

	return ret;

}
@@ -299,7 +301,7 @@ __FORTIFY_INLINE ssize_t sized_strscpy(char * const POS p, const char * const PO 
	 * p_size.

	 */

	if (len > p_size)

		fortify_panic(FORTIFY_FUNC_strscpy, FORTIFY_WRITE);

		fortify_panic(FORTIFY_FUNC_strscpy, FORTIFY_WRITE, -E2BIG);



	/*

	 * We can now safely call vanilla strscpy because we are protected from:
@@ -357,7 +359,7 @@ size_t strlcat(char * const POS p, const char * const POS q, size_t avail) 


	/* Give up if string is already overflowed. */

	if (p_size <= p_len)

		fortify_panic(FORTIFY_FUNC_strlcat, FORTIFY_READ);

		fortify_panic(FORTIFY_FUNC_strlcat, FORTIFY_READ, wanted);



	if (actual >= avail) {

		copy_len = avail - p_len - 1;
@@ -366,7 +368,7 @@ size_t strlcat(char * const POS p, const char * const POS q, size_t avail) 


	/* Give up if copy will overflow. */

	if (p_size <= actual)

		fortify_panic(FORTIFY_FUNC_strlcat, FORTIFY_WRITE);

		fortify_panic(FORTIFY_FUNC_strlcat, FORTIFY_WRITE, wanted);

	__underlying_memcpy(p + p_len, q, copy_len);

	p[actual] = '\0';
@@ -395,7 +397,7 @@ char *strcat(char * const POS p, const char *q) 
	const size_t p_size = __member_size(p);



	if (strlcat(p, q, p_size) >= p_size)

		fortify_panic(FORTIFY_FUNC_strcat, FORTIFY_WRITE);

		fortify_panic(FORTIFY_FUNC_strcat, FORTIFY_WRITE, p);

	return p;

}
@@ -431,13 +433,13 @@ char *strncat(char * const POS p, const char * const POS q, __kernel_size_t coun 
	p_len = strlen(p);

	copy_len = strnlen(q, count);

	if (p_size < p_len + copy_len + 1)

		fortify_panic(FORTIFY_FUNC_strncat, FORTIFY_WRITE);

		fortify_panic(FORTIFY_FUNC_strncat, FORTIFY_WRITE, p);

	__underlying_memcpy(p + p_len, q, copy_len);

	p[p_len + copy_len] = '\0';

	return p;

}



__FORTIFY_INLINE void fortify_memset_chk(__kernel_size_t size,

__FORTIFY_INLINE bool fortify_memset_chk(__kernel_size_t size,

					 const size_t p_size,

					 const size_t p_size_field)

{
@@ -472,7 +474,8 @@ __FORTIFY_INLINE void fortify_memset_chk(__kernel_size_t size, 
	 * lengths are unknown.)

	 */

	if (p_size != SIZE_MAX && p_size < size)

		fortify_panic(FORTIFY_FUNC_memset, FORTIFY_WRITE);

		fortify_panic(FORTIFY_FUNC_memset, FORTIFY_WRITE, true);

	return false;

}



#define __fortify_memset_chk(p, c, size, p_size, p_size_field) ({	\
@@ -571,9 +574,9 @@ __FORTIFY_INLINE bool fortify_memcpy_chk(__kernel_size_t size, 
	 * lengths are unknown.)

	 */

	if (p_size != SIZE_MAX && p_size < size)

		fortify_panic(func, FORTIFY_WRITE);

		fortify_panic(func, FORTIFY_WRITE, true);

	else if (q_size != SIZE_MAX && q_size < size)

		fortify_panic(func, FORTIFY_READ);

		fortify_panic(func, FORTIFY_READ, true);



	/*

	 * Warn when writing beyond destination field size.
@@ -673,7 +676,7 @@ __FORTIFY_INLINE void *memscan(void * const POS0 p, int c, __kernel_size_t size) 
	if (__compiletime_lessthan(p_size, size))

		__read_overflow();

	if (p_size < size)

		fortify_panic(FORTIFY_FUNC_memscan, FORTIFY_READ);

		fortify_panic(FORTIFY_FUNC_memscan, FORTIFY_READ, NULL);

	return __real_memscan(p, c, size);

}
@@ -690,7 +693,7 @@ int memcmp(const void * const POS0 p, const void * const POS0 q, __kernel_size_t 
			__read_overflow2();

	}

	if (p_size < size || q_size < size)

		fortify_panic(FORTIFY_FUNC_memcmp, FORTIFY_READ);

		fortify_panic(FORTIFY_FUNC_memcmp, FORTIFY_READ, INT_MIN);

	return __underlying_memcmp(p, q, size);

}
@@ -702,7 +705,7 @@ void *memchr(const void * const POS0 p, int c, __kernel_size_t size) 
	if (__compiletime_lessthan(p_size, size))

		__read_overflow();

	if (p_size < size)

		fortify_panic(FORTIFY_FUNC_memchr, FORTIFY_READ);

		fortify_panic(FORTIFY_FUNC_memchr, FORTIFY_READ, NULL);

	return __underlying_memchr(p, c, size);

}
@@ -714,7 +717,7 @@ __FORTIFY_INLINE void *memchr_inv(const void * const POS0 p, int c, size_t size) 
	if (__compiletime_lessthan(p_size, size))

		__read_overflow();

	if (p_size < size)

		fortify_panic(FORTIFY_FUNC_memchr_inv, FORTIFY_READ);

		fortify_panic(FORTIFY_FUNC_memchr_inv, FORTIFY_READ, NULL);

	return __real_memchr_inv(p, c, size);

}
@@ -727,7 +730,7 @@ __FORTIFY_INLINE void *kmemdup(const void * const POS0 p, size_t size, gfp_t gfp 
	if (__compiletime_lessthan(p_size, size))

		__read_overflow();

	if (p_size < size)

		fortify_panic(FORTIFY_FUNC_kmemdup, FORTIFY_READ);

		fortify_panic(FORTIFY_FUNC_kmemdup, FORTIFY_READ, NULL);

	return __real_kmemdup(p, size, gfp);

}
@@ -764,7 +767,7 @@ char *strcpy(char * const POS p, const char * const POS q) 
		__write_overflow();

	/* Run-time check for dynamic size overflow. */

	if (p_size < size)

		fortify_panic(FORTIFY_FUNC_strcpy, FORTIFY_WRITE);

		fortify_panic(FORTIFY_FUNC_strcpy, FORTIFY_WRITE, p);

	__underlying_memcpy(p, q, size);

	return p;

}

lib/fortify_kunit.c

+41 −0
Original line number Diff line number Diff line
@@ -15,8 +15,17 @@ 
 */

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt



/* Redefine fortify_panic() to track failures. */

void fortify_add_kunit_error(int write);

#define fortify_panic(func, write, retfail) do {			\

	__fortify_report(FORTIFY_REASON(func, write));			\

	fortify_add_kunit_error(write);					\

	return (retfail);						\

} while (0)



#include <kunit/device.h>

#include <kunit/test.h>

#include <kunit/test-bug.h>

#include <linux/device.h>

#include <linux/slab.h>

#include <linux/string.h>
@@ -27,10 +36,34 @@ 
# define __compiletime_strlen __builtin_strlen

#endif



static struct kunit_resource read_resource;

static struct kunit_resource write_resource;

static int fortify_read_overflows;

static int fortify_write_overflows;



static const char array_of_10[] = "this is 10";

static const char *ptr_of_11 = "this is 11!";

static char array_unknown[] = "compiler thinks I might change";



void fortify_add_kunit_error(int write)

{

	struct kunit_resource *resource;

	struct kunit *current_test;



	current_test = kunit_get_current_test();

	if (!current_test)

		return;



	resource = kunit_find_named_resource(current_test,

			write ? "fortify_write_overflows"

			      : "fortify_read_overflows");

	if (!resource)

		return;



	(*(int *)resource->data)++;

	kunit_put_resource(resource);

}



static void known_sizes_test(struct kunit *test)

{

	KUNIT_EXPECT_EQ(test, __compiletime_strlen("88888888"), 8);
@@ -318,6 +351,14 @@ static int fortify_test_init(struct kunit *test) 
	if (!IS_ENABLED(CONFIG_FORTIFY_SOURCE))

		kunit_skip(test, "Not built with CONFIG_FORTIFY_SOURCE=y");



	fortify_read_overflows = 0;

	kunit_add_named_resource(test, NULL, NULL, &read_resource,

				 "fortify_read_overflows",

				 &fortify_read_overflows);

	fortify_write_overflows = 0;

	kunit_add_named_resource(test, NULL, NULL, &write_resource,

				 "fortify_write_overflows",

				 &fortify_write_overflows);

	return 0;

}

lib/string_helpers.c

+2 −0
Original line number Diff line number Diff line
@@ -18,6 +18,8 @@ 
#include <linux/slab.h>

#include <linux/string.h>

#include <linux/string_helpers.h>

#include <kunit/test.h>

#include <kunit/test-bug.h>



/**

 * string_get_size - get the size in the specified units