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>

1 files changed, 23 insertions, 20 deletions

diff --git a/include/linux/fortify-string.h b/include/linux/fortify-string.h
index 4f6767dcd933..fbfb90479b8f 100644
--- 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;
 }