dm: introduce audit event module for device mapper

To be able to send auditing events to user space, we introduce a
generic dm-audit module. It provides helper functions to emit audit
events through the kernel audit subsystem. We claim the
AUDIT_DM_CTRL type=1336 and AUDIT_DM_EVENT type=1337 out of the
audit event messages range in the corresponding userspace api in
'include/uapi/linux/audit.h' for those events.

AUDIT_DM_CTRL is used to provide information about creation and
destruction of device mapper targets which are triggered by user space
admin control actions.
AUDIT_DM_EVENT is used to provide information about actual errors
during operation of the mapped device, showing e.g. integrity
violations in audit log.

Following commits to device mapper targets actually will make use of
this to emit those events in relevant cases.

The audit logs look like this if executing the following simple test:

 # dd if=/dev/zero of=test.img bs=1M count=1024
 # losetup -f test.img
 # integritysetup -vD format --integrity sha256 -t 32 /dev/loop0
 # integritysetup open -D /dev/loop0 --integrity sha256 integritytest
 # integritysetup status integritytest
 # integritysetup close integritytest
 # integritysetup open -D /dev/loop0 --integrity sha256 integritytest
 # integritysetup status integritytest
 # dd if=/dev/urandom of=/dev/loop0 bs=512 count=1 seek=100000
 # dd if=/dev/mapper/integritytest of=/dev/null

-------------------------
audit.log from auditd

type=UNKNOWN[1336] msg=audit(1630425039.363:184): module=integrity
op=ctr ppid=3807 pid=3819 auid=1000 uid=0 gid=0 euid=0 suid=0 fsuid=0
egid=0 sgid=0 fsgid=0 tty=pts2 ses=3 comm="integritysetup"
exe="/sbin/integritysetup" subj==unconfined dev=254:3
error_msg='success' res=1
type=UNKNOWN[1336] msg=audit(1630425039.471:185): module=integrity
op=dtr ppid=3807 pid=3819 auid=1000 uid=0 gid=0 euid=0 suid=0 fsuid=0
egid=0 sgid=0 fsgid=0 tty=pts2 ses=3 comm="integritysetup"
exe="/sbin/integritysetup" subj==unconfined dev=254:3
error_msg='success' res=1
type=UNKNOWN[1336] msg=audit(1630425039.611:186): module=integrity
op=ctr ppid=3807 pid=3819 auid=1000 uid=0 gid=0 euid=0 suid=0 fsuid=0
egid=0 sgid=0 fsgid=0 tty=pts2 ses=3 comm="integritysetup"
exe="/sbin/integritysetup" subj==unconfined dev=254:3
error_msg='success' res=1
type=UNKNOWN[1336] msg=audit(1630425054.475:187): module=integrity
op=dtr ppid=3807 pid=3819 auid=1000 uid=0 gid=0 euid=0 suid=0 fsuid=0
egid=0 sgid=0 fsgid=0 tty=pts2 ses=3 comm="integritysetup"
exe="/sbin/integritysetup" subj==unconfined dev=254:3
error_msg='success' res=1

type=UNKNOWN[1336] msg=audit(1630425073.171:191): module=integrity
op=ctr ppid=3807 pid=3883 auid=1000 uid=0 gid=0 euid=0 suid=0 fsuid=0
egid=0 sgid=0 fsgid=0 tty=pts2 ses=3 comm="integritysetup"
exe="/sbin/integritysetup" subj==unconfined dev=254:3
error_msg='success' res=1

type=UNKNOWN[1336] msg=audit(1630425087.239:192): module=integrity
op=dtr ppid=3807 pid=3902 auid=1000 uid=0 gid=0 euid=0 suid=0 fsuid=0
egid=0 sgid=0 fsgid=0 tty=pts2 ses=3 comm="integritysetup"
exe="/sbin/integritysetup" subj==unconfined dev=254:3
error_msg='success' res=1

type=UNKNOWN[1336] msg=audit(1630425093.755:193): module=integrity
op=ctr ppid=3807 pid=3906 auid=1000 uid=0 gid=0 euid=0 suid=0 fsuid=0
egid=0 sgid=0 fsgid=0 tty=pts2 ses=3 comm="integritysetup"
exe="/sbin/integritysetup" subj==unconfined dev=254:3
error_msg='success' res=1

type=UNKNOWN[1337] msg=audit(1630425112.119:194): module=integrity
op=integrity-checksum dev=254:3 sector=77480 res=0
type=UNKNOWN[1337] msg=audit(1630425112.119:195): module=integrity
op=integrity-checksum dev=254:3 sector=77480 res=0
type=UNKNOWN[1337] msg=audit(1630425112.119:196): module=integrity
op=integrity-checksum dev=254:3 sector=77480 res=0
type=UNKNOWN[1337] msg=audit(1630425112.119:197): module=integrity
op=integrity-checksum dev=254:3 sector=77480 res=0
type=UNKNOWN[1337] msg=audit(1630425112.119:198): module=integrity
op=integrity-checksum dev=254:3 sector=77480 res=0
type=UNKNOWN[1337] msg=audit(1630425112.119:199): module=integrity
op=integrity-checksum dev=254:3 sector=77480 res=0
type=UNKNOWN[1337] msg=audit(1630425112.119:200): module=integrity
op=integrity-checksum dev=254:3 sector=77480 res=0
type=UNKNOWN[1337] msg=audit(1630425112.119:201): module=integrity
op=integrity-checksum dev=254:3 sector=77480 res=0
type=UNKNOWN[1337] msg=audit(1630425112.119:202): module=integrity
op=integrity-checksum dev=254:3 sector=77480 res=0
type=UNKNOWN[1337] msg=audit(1630425112.119:203): module=integrity
op=integrity-checksum dev=254:3 sector=77480 res=0

Signed-off-by: Michael Weiß <michael.weiss@aisec.fraunhofer.de>
Signed-off-by: Paul Moore <paul@paul-moore.com> # fix audit.h numbering
Signed-off-by: Mike Snitzer <snitzer@redhat.com>

1 files changed, 66 insertions, 0 deletions

diff --git a/drivers/md/dm-audit.h b/drivers/md/dm-audit.h
new file mode 100644
index 000000000000..2385f2b659be
--- /dev/null
+++ b/drivers/md/dm-audit.h
@@ -0,0 +1,66 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Creating audit records for mapped devices.
+ *
+ * Copyright (C) 2021 Fraunhofer AISEC. All rights reserved.
+ *
+ * Authors: Michael Weiß <michael.weiss@aisec.fraunhofer.de>
+ */
+
+#ifndef DM_AUDIT_H
+#define DM_AUDIT_H
+
+#include <linux/device-mapper.h>
+#include <linux/audit.h>
+
+#ifdef CONFIG_DM_AUDIT
+void dm_audit_log_bio(const char *dm_msg_prefix, const char *op,
+		      struct bio *bio, sector_t sector, int result);
+
+/*
+ * dm_audit_log_ti() is not intended to be used directly in dm modules,
+ * the wrapper functions below should be called by dm modules instead.
+ */
+void dm_audit_log_ti(int audit_type, const char *dm_msg_prefix, const char *op,
+		     struct dm_target *ti, int result);
+
+static inline void dm_audit_log_ctr(const char *dm_msg_prefix,
+				    struct dm_target *ti, int result)
+{
+	dm_audit_log_ti(AUDIT_DM_CTRL, dm_msg_prefix, "ctr", ti, result);
+}
+
+static inline void dm_audit_log_dtr(const char *dm_msg_prefix,
+				    struct dm_target *ti, int result)
+{
+	dm_audit_log_ti(AUDIT_DM_CTRL, dm_msg_prefix, "dtr", ti, result);
+}
+
+static inline void dm_audit_log_target(const char *dm_msg_prefix, const char *op,
+				       struct dm_target *ti, int result)
+{
+	dm_audit_log_ti(AUDIT_DM_EVENT, dm_msg_prefix, op, ti, result);
+}
+#else
+static inline void dm_audit_log_bio(const char *dm_msg_prefix, const char *op,
+				    struct bio *bio, sector_t sector,
+				    int result)
+{
+}
+static inline void dm_audit_log_target(const char *dm_msg_prefix,
+				       const char *op, struct dm_target *ti,
+				       int result)
+{
+}
+static inline void dm_audit_log_ctr(const char *dm_msg_prefix,
+				    struct dm_target *ti, int result)
+{
+}
+
+static inline void dm_audit_log_dtr(const char *dm_msg_prefix,
+				    struct dm_target *ti, int result)
+{
+}
+#endif
+
+#endif