[1/2] selinux: add tracepoint on denials

Commit Message

Thiébaud Weksteen Aug. 6, 2020, 8:03 a.m. UTC

The audit data currently captures which process and which target
is responsible for a denial. There is no data on where exactly in the
process that call occurred. Debugging can be made easier by being able to
reconstruct the unified kernel and userland stack traces [1]. Add a
tracepoint on the SELinux denials which can then be used by userland
(i.e. perf).

Although this patch could manually be added by each OS developer to
trouble shoot a denial, adding it to the kernel streamlines the
developers workflow.

[1] https://source.android.com/devices/tech/debug/native_stack_dump

Signed-off-by: Thiébaud Weksteen <[e-mail]>
Suggested-by: Joel Fernandes <[e-mail]>
Reviewed-by: Peter Enderborg <[e-mail]>
---
 MAINTAINERS                |  1 +
 include/trace/events/avc.h | 37 +++++++++++++++++++++++++++++++++++++
 security/selinux/avc.c     |  5 +++++
 3 files changed, 43 insertions(+)
 create mode 100644 include/trace/events/avc.h

Patch

diff --git a/MAINTAINERS b/MAINTAINERS
index c8e8232c65da..0efaea0e144c 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -15426,6 +15426,7 @@  T:	git git://git.kernel.org/pub/scm/linux/kernel/git/pcmoore/selinux.git
 F:	Documentation/ABI/obsolete/sysfs-selinux-checkreqprot
 F:	Documentation/ABI/obsolete/sysfs-selinux-disable
 F:	Documentation/admin-guide/LSM/SELinux.rst
+F:	include/trace/events/avc.h
 F:	include/uapi/linux/selinux_netlink.h
 F:	scripts/selinux/
 F:	security/selinux/
diff --git a/include/trace/events/avc.h b/include/trace/events/avc.h
new file mode 100644
index 000000000000..07c058a9bbcd
--- /dev/null
+++ b/include/trace/events/avc.h
@@ -0,0 +1,37 @@ 
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Author: Thiébaud Weksteen <[e-mail]>
+ */
+#undef TRACE_SYSTEM
+#define TRACE_SYSTEM avc
+
+#if !defined(_TRACE_SELINUX_H) || defined(TRACE_HEADER_MULTI_READ)
+#define _TRACE_SELINUX_H
+
+#include <linux/tracepoint.h>
+
+TRACE_EVENT(selinux_audited,
+
+	TP_PROTO(struct selinux_audit_data *sad),
+
+	TP_ARGS(sad),
+
+	TP_STRUCT__entry(
+		__field(unsigned int, tclass)
+		__field(unsigned int, audited)
+	),
+
+	TP_fast_assign(
+		__entry->tclass = sad->tclass;
+		__entry->audited = sad->audited;
+	),
+
+	TP_printk("tclass=%u audited=%x",
+		__entry->tclass,
+		__entry->audited)
+);
+
+#endif
+
+/* This part must be outside protection */
+#include <trace/define_trace.h>
diff --git a/security/selinux/avc.c b/security/selinux/avc.c
index d18cb32a242a..b0a0af778b70 100644
--- a/security/selinux/avc.c
+++ b/security/selinux/avc.c
@@ -31,6 +31,9 @@ 
 #include "avc_ss.h"
 #include "classmap.h"
 
+#define CREATE_TRACE_POINTS
+#include <trace/events/avc.h>
+
 #define AVC_CACHE_SLOTS			512
 #define AVC_DEF_CACHE_THRESHOLD		512
 #define AVC_CACHE_RECLAIM		16
@@ -706,6 +709,8 @@  static void avc_audit_post_callback(struct audit_buffer *ab, void *a)
 	u32 scontext_len;
 	int rc;
 
+	trace_selinux_audited(sad);
+
 	rc = security_sid_to_context(sad->state, sad->ssid, &scontext,
 				     &scontext_len);
 	if (rc)