qla2x00t-32gbit: Avoid possible run-time warning with long model_num

The prior strlcpy() replacement of strncpy() here (which was
later replaced with strscpy()) expected pinfo->model_num (and
pinfo->model_description) to be NUL-terminated, but it is possible
it was not, as the code pattern here shows vha->hw->model_number (and
vha->hw->model_desc) being exactly 1 character larger, and the replaced
strncpy() was copying only up to the size of the source character
array. Replace this with memtostr(), which is the unambiguous way to
convert a maybe not-NUL-terminated character array into a NUL-terminated
string.

Fixes: 527e9b704c3d ("scsi: qla2xxx: Use memcpy() and strlcpy() instead of strcpy() and strncpy()")
Reviewed-by: Martin K. Petersen <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Kees Cook <[email protected]>
[ commit c3408c4ae041 upstream ]

qla2x00t-32gbit/qla_mr.c

@@ -1919,10 +1919,8 @@ qlafx00_fx_disc(scsi_qla_host_t *vha, fc_port_t *fcport, uint16_t fx_type)
 	if (fx_type == FXDISC_GET_CONFIG_INFO) {
 		struct config_info_data *pinfo =
 		    (struct config_info_data *) fdisc->u.fxiocb.rsp_addr;
-		strscpy(vha->hw->model_number, pinfo->model_num,
-			ARRAY_SIZE(vha->hw->model_number));
-		strscpy(vha->hw->model_desc, pinfo->model_description,
-			ARRAY_SIZE(vha->hw->model_desc));
+		memtostr(vha->hw->model_number, pinfo->model_num);
+		memtostr(vha->hw->model_desc, pinfo->model_description);
 		memcpy(&vha->hw->mr.symbolic_name, pinfo->symbolic_name,
 		    sizeof(vha->hw->mr.symbolic_name));
 		memcpy(&vha->hw->mr.serial_num, pinfo->serial_num,

scst/include/backport.h

@@ -1510,6 +1510,25 @@ static inline ssize_t strscpy(char *dest, const char *src, size_t count)
 }
 #endif
 
+#ifndef memtostr
+/*
+ * See also commit 0efc5990bca5 ("string.h: Introduce memtostr() and memtostr_pad()") # v6.10.
+ */
+#define memtostr(dest, src)	do {					\
+	const size_t _dest_len = __builtin_object_size(dest, 1);	\
+	const size_t _src_len = __builtin_object_size(src, 1);		\
+	const size_t _src_chars = strnlen(src, _src_len);		\
+	const size_t _copy_len = min(_dest_len - 1, _src_chars);	\
+									\
+	BUILD_BUG_ON(!__builtin_constant_p(_dest_len) ||		\
+		     !__builtin_constant_p(_src_len) ||			\
+		     _dest_len == 0 || _dest_len == (size_t)-1 ||	\
+		     _src_len == 0 || _src_len == (size_t)-1);		\
+	memcpy(dest, src, _copy_len);					\
+	dest[_copy_len] = '\0';						\
+} while (0)
+#endif
+
 /* <linux/sysfs.h> */
 
 #if LINUX_VERSION_CODE < KERNEL_VERSION(3, 11, 0) &&	\