linux-kernel - [PATCH 3/3] samples: Add sample using SECCOMP_RET

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Date:	Tue, 18 Dec 2012 16:54:45 -0500
From:	Corey Bryant <coreyb@...ux.vnet.ibm.com>
To:	linux-kernel@...r.kernel.org
Cc:	linux-security-module@...r.kernel.org, jmorris@...ei.org,
	wad@...omium.org, pmoore@...hat.com, otubo@...ux.vnet.ibm.com
Subject: [PATCH 3/3] samples: Add sample using SECCOMP_RET_INFO

Adds a sample that demonstrates use of the SECCOMP_RET_INFO return value.

Signed-off-by: Corey Bryant <coreyb@...ux.vnet.ibm.com>
---
 samples/seccomp/Makefile     |  8 ++++++-
 samples/seccomp/bpf-logger.c | 52 ++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 59 insertions(+), 1 deletion(-)
 create mode 100644 samples/seccomp/bpf-logger.c

diff --git a/samples/seccomp/Makefile b/samples/seccomp/Makefile
index bbbd276..ee769bb 100644
--- a/samples/seccomp/Makefile
+++ b/samples/seccomp/Makefile
@@ -1,7 +1,7 @@
 # kbuild trick to avoid linker error. Can be omitted if a module is built.
 obj- := dummy.o
 
-hostprogs-$(CONFIG_SECCOMP_FILTER) := bpf-fancy dropper bpf-direct
+hostprogs-$(CONFIG_SECCOMP_FILTER) := bpf-fancy dropper bpf-direct bpf-logger
 
 HOSTCFLAGS_bpf-fancy.o += -I$(objtree)/usr/include
 HOSTCFLAGS_bpf-fancy.o += -idirafter $(objtree)/include
@@ -17,6 +17,10 @@ HOSTCFLAGS_bpf-direct.o += -I$(objtree)/usr/include
 HOSTCFLAGS_bpf-direct.o += -idirafter $(objtree)/include
 bpf-direct-objs := bpf-direct.o
 
+HOSTCFLAGS_bpf-logger.o += -I$(objtree)/usr/include
+HOSTCFLAGS_bpf-logger.o += -idirafter $(objtree)/include
+bpf-logger-objs := bpf-logger.o
+
 # Try to match the kernel target.
 ifndef CONFIG_64BIT
 
@@ -31,9 +35,11 @@ HOSTCFLAGS_bpf-direct.o += $(MFLAG)
 HOSTCFLAGS_dropper.o += $(MFLAG)
 HOSTCFLAGS_bpf-helper.o += $(MFLAG)
 HOSTCFLAGS_bpf-fancy.o += $(MFLAG)
+HOSTCFLAGS_bpf-logger.o += $(MFLAG)
 HOSTLOADLIBES_bpf-direct += $(MFLAG)
 HOSTLOADLIBES_bpf-fancy += $(MFLAG)
 HOSTLOADLIBES_dropper += $(MFLAG)
+HOSTLOADLIBES_bpf-logger += $(MFLAG)
 endif
 
 # Tell kbuild to always build the programs
diff --git a/samples/seccomp/bpf-logger.c b/samples/seccomp/bpf-logger.c
new file mode 100644
index 0000000..4eee0ea
--- /dev/null
+++ b/samples/seccomp/bpf-logger.c
@@ -0,0 +1,52 @@
+/*
+ * System call logger built on seccomp_filter.
+ *
+ * Copyright (c) 2012 The Chromium OS Authors <chromium-os-dev@...omium.org>
+ * Copyright (C) IBM Corporation, 2012
+ * Authors: Will Drewry <wad@...omium.org>
+ *          Corey Bryant <coreyb@...ux.vnet.ibm.com>
+ *
+ * The code may be used by anyone for any purpose,
+ * and can serve as a starting point for developing
+ * applications using prctl(PR_SET_SECCOMP, 2, ...).
+ *
+ * Prints rate-limited informational kernel messages for
+ * each system call that the process executes.
+ *
+ * Run this one as root as PR_SET_NO_NEW_PRIVS is not called.
+ */
+
+#include <linux/filter.h>
+#include <linux/seccomp.h>
+#include <linux/unistd.h>
+#include <sys/prctl.h>
+#include <unistd.h>
+
+static int install_filter()
+{
+	struct sock_filter filter[] = {
+		BPF_STMT(BPF_RET+BPF_K, SECCOMP_RET_INFO),
+	};
+	struct sock_fprog prog = {
+		.len = (unsigned short)(sizeof(filter)/sizeof(filter[0])),
+		.filter = filter,
+	};
+	if (prctl(PR_SET_SECCOMP, 2, &prog)) {
+		perror("prctl");
+		return 1;
+	}
+	return 0;
+}
+
+#define payload(_c) (_c), sizeof((_c))
+int main(int argc, char **argv)
+{
+	int fd;
+	char msg[] = "To examine syscalls type: dmesg | grep seccomp\n";
+	if (install_filter())
+		return 1;
+	fd = syscall(__NR_dup, STDOUT_FILENO);
+	syscall(__NR_write, fd, payload(msg));
+	syscall(__NR_close, fd);
+	return 0;
+}
-- 
1.7.11.7

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