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: Kees Cook <keescook@chromium.org>

diff --git a/include/linux/fortify-string.h b/include/linux/fortify-string.h
index 4f6767dcd933e8365d01fa620bfd23c08513ac7f..fbfb90479b8f7ae60a0678df3a3c7c8fee63bf77 100644 (file)
--- a/include/linux/fortify-string.h
+++ b/include/linux/fortify-string.h
@@ -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)     \
-       __fortify_panic(FORTIFY_REASON(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;
 }

diff --git a/lib/fortify_kunit.c b/lib/fortify_kunit.c
index 7a88b5dd3d27d7aca988adb4d8f05e4684435fc5..4ba7d02fdd7812d42d51b342cfbbf0a820ada7fb 100644 (file)
--- a/lib/fortify_kunit.c
+++ b/lib/fortify_kunit.c
@@ -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;
 }
 

diff --git a/lib/string_helpers.c b/lib/string_helpers.c
index 9291dc74ae015a39e50643e0e285a6c5a5c93056..5e53d42e32bb427c8575ca1e021c3847424cc82a 100644 (file)
--- a/lib/string_helpers.c
+++ b/lib/string_helpers.c
@@ -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