lib: json: Alignment should be considered when calculating struct size

This was causing an unaligned pointer read on some architectures,
leading to crashes.  This could be alternatively solved by rounding
the size to the nearest power of 2, but this wouldn't work with
packed structs.

Signed-off-by: Leandro Pereira <[email protected]>

Author: lpereira

lib/json/json.c

@@ -9,10 +9,11 @@
 #include <errno.h>
 #include <limits.h>
 #include <misc/printk.h>
+#include <misc/util.h>
 #include <stdbool.h>
-#include <zephyr/types.h>
 #include <stdlib.h>
 #include <string.h>
+#include <zephyr/types.h>
 
 #include "json.h"
 
@@ -475,6 +476,8 @@ static int decode_value(struct json_obj *obj,
 
 static ptrdiff_t get_elem_size(const struct json_obj_descr *descr)
 {
+	assert(descr->alignment);
+
 	switch (descr->type) {
 	case JSON_TOK_NUMBER:
 		return sizeof(s32_t);
@@ -489,8 +492,10 @@ static ptrdiff_t get_elem_size(const struct json_obj_descr *descr)
 		ptrdiff_t total = 0;
 		size_t i;
 
-		for (i = 0; i < descr->sub_descr_len; i++) {
-			total += get_elem_size(&descr->object.sub_descr[i]);
+		for (i = 0; i < descr->object.sub_descr_len; i++) {
+			ptrdiff_t s = get_elem_size(&descr->object.sub_descr[i]);
+
+			total += ROUND_UP(s, descr->alignment);
 		}
 
 		return total;

lib/json/json.h

@@ -33,6 +33,7 @@ struct json_obj_descr {
 	const char *field_name;
 	size_t field_name_len;
 	size_t offset;
+	size_t alignment;
 
 	/* Valid values here: JSON_TOK_STRING, JSON_TOK_NUMBER,
 	 * JSON_TOK_TRUE, JSON_TOK_FALSE, JSON_TOK_OBJECT_START,
@@ -95,6 +96,7 @@ typedef int (*json_append_bytes_t)(const char *bytes, size_t len,
 		.field_name = (#field_name_), \
 		.field_name_len = sizeof(#field_name_) - 1, \
 		.offset = offsetof(struct_, field_name_), \
+		.alignment = __alignof__(struct_), \
 		.type = type_, \
 	}
 
@@ -128,6 +130,7 @@ typedef int (*json_append_bytes_t)(const char *bytes, size_t len,
 		.field_name = (#field_name_), \
 		.field_name_len = (sizeof(#field_name_) - 1), \
 		.offset = offsetof(struct_, field_name_), \
+		.alignment = __alignof__(struct_), \
 		.type = JSON_TOK_OBJECT_START, \
 		.object = { \
 			.sub_descr = sub_descr_, \
@@ -166,11 +169,13 @@ typedef int (*json_append_bytes_t)(const char *bytes, size_t len,
 		.field_name = (#field_name_), \
 		.field_name_len = sizeof(#field_name_) - 1, \
 		.offset = offsetof(struct_, field_name_), \
+		.alignment = __alignof__(struct_), \
 		.type = JSON_TOK_LIST_START, \
 		.array = { \
 			.element_descr = &(struct json_obj_descr) { \
 				.type = elem_type_, \
 				.offset = offsetof(struct_, len_field_), \
+				.alignment = __alignof__(struct_), \
 			}, \
 			.n_elements = (max_len_), \
 		}, \
@@ -221,6 +226,7 @@ typedef int (*json_append_bytes_t)(const char *bytes, size_t len,
 		.field_name = (#field_name_), \
 		.field_name_len = sizeof(#field_name_) - 1, \
 		.offset = offsetof(struct_, field_name_), \
+		.alignment = __alignof__(struct_), \
 		.type = JSON_TOK_LIST_START, \
 		.array = { \
 			.element_descr = &(struct json_obj_descr) { \
@@ -230,6 +236,7 @@ typedef int (*json_append_bytes_t)(const char *bytes, size_t len,
 					.sub_descr_len = elem_descr_len_, \
 				}, \
 				.offset = offsetof(struct_, len_field_), \
+				.alignment = __alignof__(struct_), \
 			}, \
 			.n_elements = (max_len_), \
 		}, \
@@ -258,6 +265,7 @@ typedef int (*json_append_bytes_t)(const char *bytes, size_t len,
 		.field_name = (json_field_name_), \
 		.field_name_len = sizeof(json_field_name_) - 1, \
 		.offset = offsetof(struct_, struct_field_name_), \
+		.alignment = __alignof__(struct_), \
 		.type = type_, \
 	}
 
@@ -283,6 +291,7 @@ typedef int (*json_append_bytes_t)(const char *bytes, size_t len,
 		.field_name = (json_field_name_), \
 		.field_name_len = (sizeof(json_field_name_) - 1), \
 		.offset = offsetof(struct_, struct_field_name_), \
+		.alignment = __alignof__(struct_), \
 		.type = JSON_TOK_OBJECT_START, \
 		.object = { \
 			.sub_descr = sub_descr_, \
@@ -318,11 +327,13 @@ typedef int (*json_append_bytes_t)(const char *bytes, size_t len,
 		.field_name = (json_field_name_), \
 		.field_name_len = sizeof(json_field_name_) - 1, \
 		.offset = offsetof(struct_, struct_field_name_), \
+		.alignment = __alignof__(struct_), \
 		.type = JSON_TOK_LIST_START, \
 		.array = { \
 			.element_descr = &(struct json_obj_descr) { \
 				.type = elem_type_, \
 				.offset = offsetof(struct_, len_field_), \
+				.alignment = __alignof__(struct_), \
 			}, \
 			.n_elements = (max_len_), \
 		}, \
@@ -382,6 +393,7 @@ typedef int (*json_append_bytes_t)(const char *bytes, size_t len,
 		.field_name = json_field_name_, \
 		.field_name_len = sizeof(json_field_name_) - 1, \
 		.offset = offsetof(struct_, struct_field_name_), \
+		.alignment = __alignof__(struct_), \
 		.type = JSON_TOK_LIST_START, \
 		.element_descr = &(struct json_obj_descr) { \
 			.type = JSON_TOK_OBJECT_START, \
@@ -390,6 +402,7 @@ typedef int (*json_append_bytes_t)(const char *bytes, size_t len,
 				.sub_descr_len = elem_descr_len_, \
 			}, \
 			.offset = offsetof(struct_, len_field_), \
+			.alignment = __alignof__(struct_), \
 		}, \
 		.n_elements = (max_len_), \
 	}