api: provide 32-bit friendly argument comparison macros

We have a longstanding issue with 32-bit to 64-bit sign extension
inadvertently resulting in bogus syscall argument extensions. This
patch introduces a new set of argument comparison macros which
limit the argument values to 32-bit values so that we don't run into
problems with sign extension.

We use the macro overloading proposed by Roman at
https://kecher.net/overloading-macros/ to retain the feature of these
macros being usable as static initializers.

Thanks to @jdstrand on GitHub for reporting the problem.

Signed-off-by: Paul Moore <paul@paul-moore.com>
Signed-off-by: Michael Weiser <michael.weiser@gmx.de>

1 files changed, 73 insertions, 14 deletions

diff --git a/include/seccomp.h.in b/include/seccomp.h.in
index 20ce45e..b28e76e 100644
--- a/include/seccomp.h.in
+++ b/include/seccomp.h.in
@@ -198,44 +198,103 @@ struct scmp_arg_cmp {
  */
 #define SCMP_SYS(x)		(__NR_##x)
 
+/* Helpers for the argument comparison macros, DO NOT USE directly */
+#define _SCMP_VA_NUM_ARGS(...)	_SCMP_VA_NUM_ARGS_IMPL(__VA_ARGS__,2,1)
+#define _SCMP_VA_NUM_ARGS_IMPL(_1,_2,N,...)	N
+#define _SCMP_MACRO_DISPATCHER(func, ...) \
+	_SCMP_MACRO_DISPATCHER_IMPL1(func, _SCMP_VA_NUM_ARGS(__VA_ARGS__))
+#define _SCMP_MACRO_DISPATCHER_IMPL1(func, nargs) \
+	_SCMP_MACRO_DISPATCHER_IMPL2(func, nargs)
+#define _SCMP_MACRO_DISPATCHER_IMPL2(func, nargs) \
+	func ## nargs
+#define _SCMP_CMP32_1(x, y, z)		SCMP_CMP64(x, y, (uint32_t)(z))
+#define _SCMP_CMP32_2(x, y, z, q)	SCMP_CMP64(x, y, (uint32_t)(z), (uint32_t)(q))
+
 /**
- * Specify an argument comparison struct for use in declaring rules
+ * Specify a 64-bit argument comparison struct for use in declaring rules
  * @param arg the argument number, starting at 0
  * @param op the comparison operator, e.g. SCMP_CMP_*
  * @param datum_a dependent on comparison
  * @param datum_b dependent on comparison, optional
  */
-#define SCMP_CMP(...)		((struct scmp_arg_cmp){__VA_ARGS__})
+#define SCMP_CMP64(...)		((struct scmp_arg_cmp){__VA_ARGS__})
+#define SCMP_CMP		SCMP_CMP64
+
+/**
+ * Specify a 32-bit argument comparison struct for use in declaring rules
+ * @param arg the argument number, starting at 0
+ * @param op the comparison operator, e.g. SCMP_CMP_*
+ * @param datum_a dependent on comparison (32-bits)
+ * @param datum_b dependent on comparison, optional (32-bits)
+ */
+#define SCMP_CMP32(x, y, ...) \
+	_SCMP_MACRO_DISPATCHER(_SCMP_CMP32_, __VA_ARGS__)(x, y, __VA_ARGS__)
+
+/**
+ * Specify a 64-bit argument comparison struct for argument 0
+ */
+#define SCMP_A0_64(...)		SCMP_CMP64(0, __VA_ARGS__)
+#define SCMP_A0			SCMP_A0_64
+
+/**
+ * Specify a 32-bit argument comparison struct for argument 0
+ */
+#define SCMP_A0_32(x, ...)	SCMP_CMP32(0, x, __VA_ARGS__)
+
+/**
+ * Specify a 64-bit argument comparison struct for argument 1
+ */
+#define SCMP_A1_64(...)		SCMP_CMP64(1, __VA_ARGS__)
+#define SCMP_A1			SCMP_A1_64
+
+/**
+ * Specify a 32-bit argument comparison struct for argument 1
+ */
+#define SCMP_A1_32(x, ...)	SCMP_CMP32(1, x, __VA_ARGS__)
+
+/**
+ * Specify a 64-bit argument comparison struct for argument 2
+ */
+#define SCMP_A2_64(...)		SCMP_CMP64(2, __VA_ARGS__)
+#define SCMP_A2			SCMP_A2_64
+
+/**
+ * Specify a 32-bit argument comparison struct for argument 2
+ */
+#define SCMP_A2_32(x, ...)	SCMP_CMP32(2, x, __VA_ARGS__)
 
 /**
- * Specify an argument comparison struct for argument 0
+ * Specify a 64-bit argument comparison struct for argument 3
  */
-#define SCMP_A0(...)		SCMP_CMP(0, __VA_ARGS__)
+#define SCMP_A3_64(...)		SCMP_CMP64(3, __VA_ARGS__)
+#define SCMP_A3			SCMP_A3_64
 
 /**
- * Specify an argument comparison struct for argument 1
+ * Specify a 32-bit argument comparison struct for argument 3
  */
-#define SCMP_A1(...)		SCMP_CMP(1, __VA_ARGS__)
+#define SCMP_A3_32(x, ...)	SCMP_CMP32(3, x, __VA_ARGS__)
 
 /**
- * Specify an argument comparison struct for argument 2
+ * Specify a 64-bit argument comparison struct for argument 4
  */
-#define SCMP_A2(...)		SCMP_CMP(2, __VA_ARGS__)
+#define SCMP_A4_64(...)		SCMP_CMP64(4, __VA_ARGS__)
+#define SCMP_A4			SCMP_A4_64
 
 /**
- * Specify an argument comparison struct for argument 3
+ * Specify a 32-bit argument comparison struct for argument 4
  */
-#define SCMP_A3(...)		SCMP_CMP(3, __VA_ARGS__)
+#define SCMP_A4_32(x, ...)	SCMP_CMP32(4, x, __VA_ARGS__)
 
 /**
- * Specify an argument comparison struct for argument 4
+ * Specify a 64-bit argument comparison struct for argument 5
  */
-#define SCMP_A4(...)		SCMP_CMP(4, __VA_ARGS__)
+#define SCMP_A5_64(...)		SCMP_CMP64(5, __VA_ARGS__)
+#define SCMP_A5			SCMP_A5_64
 
 /**
- * Specify an argument comparison struct for argument 5
+ * Specify a 32-bit argument comparison struct for argument 5
  */
-#define SCMP_A5(...)		SCMP_CMP(5, __VA_ARGS__)
+#define SCMP_A5_32(x, ...)	SCMP_CMP32(5, x, __VA_ARGS__)
 
 /*
  * seccomp actions