hfsplus: use struct_group_attr() for memcpy() region

In preparation for FORTIFY_SOURCE performing compile-time and run-time
field bounds checking for memset(), avoid intentionally writing across
neighboring fields.

Add struct_group() to mark the "info" region (containing struct DInfo
and struct DXInfo structs) in struct hfsplus_cat_folder and struct
hfsplus_cat_file that are written into directly, so the compiler can
correctly reason about the expected size of the writes.

"pahole" shows no size nor member offset changes to struct
hfsplus_cat_folder nor struct hfsplus_cat_file.  "objdump -d" shows no
object code changes.

Link: https://lkml.kernel.org/r/20211119192851.1046717-1-keescook@chromium.org
Signed-off-by: Kees Cook <keescook@chromium.org>
Acked-by: Christian Brauner <christian.brauner@ubuntu.com>
Cc: Zhen Lei <thunder.leizhen@huawei.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Author: kees

fs/hfsplus/hfsplus_raw.h

@@ -260,8 +260,10 @@ struct hfsplus_cat_folder {
 	__be32 access_date;
 	__be32 backup_date;
 	struct hfsplus_perm permissions;
-	struct DInfo user_info;
-	struct DXInfo finder_info;
+	struct_group_attr(info, __packed,
+		struct DInfo user_info;
+		struct DXInfo finder_info;
+	);
 	__be32 text_encoding;
 	__be32 subfolders;	/* Subfolder count in HFSX. Reserved in HFS+. */
 } __packed;
@@ -294,8 +296,10 @@ struct hfsplus_cat_file {
 	__be32 access_date;
 	__be32 backup_date;
 	struct hfsplus_perm permissions;
-	struct FInfo user_info;
-	struct FXInfo finder_info;
+	struct_group_attr(info, __packed,
+		struct FInfo user_info;
+		struct FXInfo finder_info;
+	);
 	__be32 text_encoding;
 	u32 reserved2;
 

fs/hfsplus/xattr.c

@@ -296,7 +296,7 @@ int __hfsplus_setxattr(struct inode *inode, const char *name,
 					sizeof(hfsplus_cat_entry));
 		if (be16_to_cpu(entry.type) == HFSPLUS_FOLDER) {
 			if (size == folder_finderinfo_len) {
-				memcpy(&entry.folder.user_info, value,
+				memcpy(&entry.folder.info, value,
 						folder_finderinfo_len);
 				hfs_bnode_write(cat_fd.bnode, &entry,
 					cat_fd.entryoffset,
@@ -309,7 +309,7 @@ int __hfsplus_setxattr(struct inode *inode, const char *name,
 			}
 		} else if (be16_to_cpu(entry.type) == HFSPLUS_FILE) {
 			if (size == file_finderinfo_len) {
-				memcpy(&entry.file.user_info, value,
+				memcpy(&entry.file.info, value,
 						file_finderinfo_len);
 				hfs_bnode_write(cat_fd.bnode, &entry,
 					cat_fd.entryoffset,