[PATCH v2 6/8] selinux: do not include <linux/*.h> headers from host programs

[Daniel Gomez via B4 Relay]

From: Masahiro Yamada <masahiroy at kernel.org>

Commit bfc5e3a6af39 ("selinux: use the kernel headers when building
scripts/selinux") is not the right thing to do.

It is clear from the warning in include/uapi/linux/types.h:

  #ifndef __EXPORTED_HEADERS__
  #warning "Attempt to use kernel headers from user space, see https://kernelnewbies.org/KernelHeaders"
  #endif /* __EXPORTED_HEADERS__ */

If you are inclined to define __EXPORTED_HEADERS__, you are likely doing
wrong.

Adding the comment:

  /* NOTE: we really do want to use the kernel headers here */

does not justify the hack in any way.

Currently, <linux/*.h> headers are included for the following purposes:

 - <linux/capability.h> is included to check CAP_LAST_CAP
 - <linux/socket.h> in included to check PF_MAX

We can skip these checks when building host programs, as they will
be eventually tested when building the kernel space.

I got rid of <linux/stddef.h> from initial_sid_to_string.h because
it is likely that NULL is already defined. If you insist on making
it self-contained, you can add the following:

  #ifdef __KERNEL__
  #include <linux/stddef.h>
  #else
  #include <stddef.h>
  #endif

scripts/selinux/mdp/mdp.c still includes <linux/kconfig.h>, which is
also discouraged and should be fixed by a follow-up refactoring.

Signed-off-by: Masahiro Yamada <masahiroy at kernel.org>
---
 scripts/selinux/genheaders/Makefile              |  4 +---
 scripts/selinux/genheaders/genheaders.c          |  3 ---
 scripts/selinux/mdp/Makefile                     |  2 +-
 scripts/selinux/mdp/mdp.c                        |  4 ----
 security/selinux/include/classmap.h              | 19 ++++++++++++-------
 security/selinux/include/initial_sid_to_string.h |  2 --
 6 files changed, 14 insertions(+), 20 deletions(-)

diff --git a/scripts/selinux/genheaders/Makefile b/scripts/selinux/genheaders/Makefile
index 1faf7f07e8db..866f60e78882 100644
--- a/scripts/selinux/genheaders/Makefile
+++ b/scripts/selinux/genheaders/Makefile
@@ -1,5 +1,3 @@
 # SPDX-License-Identifier: GPL-2.0
 hostprogs-always-y += genheaders
-HOST_EXTRACFLAGS += \
-	-I$(srctree)/include/uapi -I$(srctree)/include \
-	-I$(srctree)/security/selinux/include
+HOST_EXTRACFLAGS += -I$(srctree)/security/selinux/include
diff --git a/scripts/selinux/genheaders/genheaders.c b/scripts/selinux/genheaders/genheaders.c
index 15520806889e..3834d7eb0af6 100644
--- a/scripts/selinux/genheaders/genheaders.c
+++ b/scripts/selinux/genheaders/genheaders.c
@@ -1,8 +1,5 @@
 // SPDX-License-Identifier: GPL-2.0
 
-/* NOTE: we really do want to use the kernel headers here */
-#define __EXPORTED_HEADERS__
-
 #include <stdio.h>
 #include <stdlib.h>
 #include <unistd.h>
diff --git a/scripts/selinux/mdp/Makefile b/scripts/selinux/mdp/Makefile
index d61058ddd15c..673782e3212f 100644
--- a/scripts/selinux/mdp/Makefile
+++ b/scripts/selinux/mdp/Makefile
@@ -1,7 +1,7 @@
 # SPDX-License-Identifier: GPL-2.0
 hostprogs-always-y += mdp
 HOST_EXTRACFLAGS += \
-	-I$(srctree)/include/uapi -I$(srctree)/include \
+	-I$(srctree)/include \
 	-I$(srctree)/security/selinux/include -I$(objtree)/include
 
 clean-files	:= policy.* file_contexts
diff --git a/scripts/selinux/mdp/mdp.c b/scripts/selinux/mdp/mdp.c
index 1415604c3d24..52365921c043 100644
--- a/scripts/selinux/mdp/mdp.c
+++ b/scripts/selinux/mdp/mdp.c
@@ -11,10 +11,6 @@
  * Authors: Serge E. Hallyn <serue at us.ibm.com>
  */
 
-
-/* NOTE: we really do want to use the kernel headers here */
-#define __EXPORTED_HEADERS__
-
 #include <stdio.h>
 #include <stdlib.h>
 #include <unistd.h>
diff --git a/security/selinux/include/classmap.h b/security/selinux/include/classmap.h
index 7229c9bf6c27..518209e1beb0 100644
--- a/security/selinux/include/classmap.h
+++ b/security/selinux/include/classmap.h
@@ -1,8 +1,5 @@
 /* SPDX-License-Identifier: GPL-2.0 */
 
-#include <linux/capability.h>
-#include <linux/socket.h>
-
 #define COMMON_FILE_SOCK_PERMS                                            \
 	"ioctl", "read", "write", "create", "getattr", "setattr", "lock", \
 		"relabelfrom", "relabelto", "append", "map"
@@ -36,10 +33,6 @@
 	"mac_override", "mac_admin", "syslog", "wake_alarm", "block_suspend", \
 		"audit_read", "perfmon", "bpf", "checkpoint_restore"
 
-#if CAP_LAST_CAP > CAP_CHECKPOINT_RESTORE
-#error New capability defined, please update COMMON_CAP2_PERMS.
-#endif
-
 /*
  * Note: The name for any socket class should be suffixed by "socket",
  *	 and doesn't contain more than one substr of "socket".
@@ -181,6 +174,18 @@ const struct security_class_mapping secclass_map[] = {
 	{ NULL }
 };
 
+#ifdef __KERNEL__ /* avoid this check when building host programs */
+
+#include <linux/capability.h>
+
+#if CAP_LAST_CAP > CAP_CHECKPOINT_RESTORE
+#error New capability defined, please update COMMON_CAP2_PERMS.
+#endif
+
+#include <linux/socket.h>
+
 #if PF_MAX > 46
 #error New address family defined, please update secclass_map.
 #endif
+
+#endif /* __KERNEL__ */
diff --git a/security/selinux/include/initial_sid_to_string.h b/security/selinux/include/initial_sid_to_string.h
index 99b353b2abb4..f683a78b21fd 100644
--- a/security/selinux/include/initial_sid_to_string.h
+++ b/security/selinux/include/initial_sid_to_string.h
@@ -1,7 +1,5 @@
 /* SPDX-License-Identifier: GPL-2.0 */
 
-#include <linux/stddef.h>
-
 static const char *const initial_sid_to_string[] = {
 	NULL, /* zero placeholder, not used */
 	"kernel", /* kernel / SECINITSID_KERNEL */

-- 
2.46.0