stddef.h: Introduce sizeof_field()

kees · kees · commit 4229a470175b · 2018-01-15T12:07:46.000-08:00
The size of fields within a structure is needed in a few places in the
kernel already, and will be needed for the usercopy whitelisting when
declaring whitelist regions within structures. This creates a dedicated
macro and redefines offsetofend() to use it.

Existing usage, ignoring the 1200+ lustre assert uses:

$ git grep -E 'sizeof$\(\((struct )?[a-zA-Z_]+ \*$0\)-&gt;' | \
	grep -v staging/lustre | wc -l
65

Signed-off-by: Kees Cook &lt;keescook@chromium.org&gt;
diff --git a/include/linux/stddef.h b/include/linux/stddef.h
@@ -19,13 +19,21 @@ enum {
 #define offsetof(TYPE, MEMBER)	((size_t)&((TYPE *)0)->MEMBER)
 #endif
 
+/**
+ * sizeof_field(TYPE, MEMBER)
+ *
+ * @TYPE: The structure containing the field of interest
+ * @MEMBER: The field to return the size of
+ */
+#define sizeof_field(TYPE, MEMBER) sizeof((((TYPE *)0)->MEMBER))
+
 /**
  * offsetofend(TYPE, MEMBER)
  *
  * @TYPE: The type of the structure
  * @MEMBER: The member within the structure to get the end offset of
  */
 #define offsetofend(TYPE, MEMBER) \
-	(offsetof(TYPE, MEMBER)	+ sizeof(((TYPE *)0)->MEMBER))
+	(offsetof(TYPE, MEMBER)	+ sizeof_field(TYPE, MEMBER))
 
 #endif
