Re: [dm-devel] [PATCH v3 1/3] dm: introduce audit event module for device mapper

[Paul Moore <paul@paul-moore.com>]

On Tue, Aug 31, 2021 at 3:19 PM Michael Weiß
<michael.weiss@aisec.fraunhofer.de> wrote:
>
> 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>
> ---
>  drivers/md/Kconfig         | 10 +++++
>  drivers/md/Makefile        |  4 ++
>  drivers/md/dm-audit.c      | 79 ++++++++++++++++++++++++++++++++++++++
>  drivers/md/dm-audit.h      | 62 ++++++++++++++++++++++++++++++
>  include/uapi/linux/audit.h |  2 +
>  5 files changed, 157 insertions(+)
>  create mode 100644 drivers/md/dm-audit.c
>  create mode 100644 drivers/md/dm-audit.h
>
> diff --git a/drivers/md/Kconfig b/drivers/md/Kconfig
> index 0602e82a9516..48adbec12148 100644
> --- a/drivers/md/Kconfig
> +++ b/drivers/md/Kconfig
> @@ -608,6 +608,7 @@ config DM_INTEGRITY
>         select CRYPTO
>         select CRYPTO_SKCIPHER
>         select ASYNC_XOR
> +       select DM_AUDIT if AUDIT
>         help
>           This device-mapper target emulates a block device that has
>           additional per-sector tags that can be used for storing
> @@ -640,4 +641,13 @@ config DM_ZONED
>
>           If unsure, say N.
>
> +config DM_AUDIT
> +       bool "DM audit events"
> +       depends on AUDIT
> +       help
> +         Generate audit events for device-mapper.
> +
> +         Enables audit logging of several security relevant events in the
> +         particular device-mapper targets, especially the integrity target.
> +
>  endif # MD
> diff --git a/drivers/md/Makefile b/drivers/md/Makefile
> index a74aaf8b1445..2f83d649500d 100644
> --- a/drivers/md/Makefile
> +++ b/drivers/md/Makefile
> @@ -103,3 +103,7 @@ endif
>  ifeq ($(CONFIG_DM_VERITY_VERIFY_ROOTHASH_SIG),y)
>  dm-verity-objs                 += dm-verity-verify-sig.o
>  endif
> +
> +ifeq ($(CONFIG_DM_AUDIT),y)
> +dm-mod-objs                    += dm-audit.o
> +endif
> diff --git a/drivers/md/dm-audit.c b/drivers/md/dm-audit.c
> new file mode 100644
> index 000000000000..761ecfdcd49a
> --- /dev/null
> +++ b/drivers/md/dm-audit.c
> @@ -0,0 +1,79 @@
> +// 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>
> + */
> +
> +#include <linux/audit.h>
> +#include <linux/module.h>
> +#include <linux/device-mapper.h>
> +#include <linux/bio.h>
> +#include <linux/blkdev.h>
> +
> +#include "dm-audit.h"
> +#include "dm-core.h"
> +
> +static struct audit_buffer *dm_audit_log_start(int audit_type,
> +                                              const char *dm_msg_prefix,
> +                                              const char *op)
> +{
> +       struct audit_buffer *ab;
> +
> +       if (audit_enabled == AUDIT_OFF)
> +               return NULL;
> +
> +       ab = audit_log_start(audit_context(), GFP_KERNEL, audit_type);
> +       if (unlikely(!ab))
> +               return NULL;
> +
> +       audit_log_format(ab, "module=%s op=%s", dm_msg_prefix, op);
> +       return ab;
> +}
> +
> +void dm_audit_log_ti(int audit_type, const char *dm_msg_prefix, const char *op,
> +                    struct dm_target *ti, int result)
> +{
> +       struct audit_buffer *ab;
> +       struct mapped_device *md = dm_table_get_md(ti->table);
> +       int dev_major = dm_disk(md)->major;
> +       int dev_minor = dm_disk(md)->first_minor;
> +
> +       ab = dm_audit_log_start(audit_type, dm_msg_prefix, op);
> +       if (unlikely(!ab))
> +               return;
> +
> +       switch (audit_type) {
> +       case AUDIT_DM_CTRL:
> +               audit_log_task_info(ab);
> +               audit_log_format(ab, " dev=%d:%d error_msg='%s'", dev_major,
> +                                dev_minor, !result ? ti->error : "success");
> +               break;
> +       case AUDIT_DM_EVENT:
> +               audit_log_format(ab, " dev=%d:%d sector=?", dev_major,
> +                                dev_minor);
> +               break;
> +       }
> +       audit_log_format(ab, " res=%d", result);
> +       audit_log_end(ab);
> +}
> +EXPORT_SYMBOL_GPL(dm_audit_log_ti);

Just checking, but are you okay when the inevitable happens and
someone passes an @audit_type that is not either AUDIT_CM_CTRL or
AUDIT_DM_EVENT?  Right now that will succeed without error and give a
rather short audit record.

> +void dm_audit_log_bio(const char *dm_msg_prefix, const char *op,
> +                     struct bio *bio, sector_t sector, int result)
> +{
> +       struct audit_buffer *ab;
> +       int dev_major = MAJOR(bio->bi_bdev->bd_dev);
> +       int dev_minor = MINOR(bio->bi_bdev->bd_dev);
> +
> +       ab = dm_audit_log_start(AUDIT_DM_EVENT, dm_msg_prefix, op);
> +       if (unlikely(!ab))
> +               return;
> +
> +       audit_log_format(ab, " dev=%d:%d sector %llu res=%d",
> +                        dev_major, dev_minor, sector, result);

I think you forgot the "=" after "sector", e.g. "sector=%llu".

> +       audit_log_end(ab);
> +}
> +EXPORT_SYMBOL_GPL(dm_audit_log_bio);

-- 
paul moore
www.paul-moore.com


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