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selinux: add basic filtering for audit trace events

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This patch adds further attributes to the event. These attributes are
helpful to understand the context of the message and can be used
to filter the events.

There are three common items. Source context, target context and tclass.
There are also items from the outcome of operation performed.

An event is similar to:
           <...>-1309  [002] ....  6346.691689: selinux_audited:
       requested=0x4000000 denied=0x4000000 audited=0x4000000
       result=-13
       scontext=system_u:system_r:cupsd_t:s0-s0:c0.c1023
       tcontext=system_u:object_r:bin_t:s0 tclass=file

With systems where many denials are occurring, it is useful to apply a
filter. The filtering is a set of logic that is inserted with
the filter file. Example:
 echo "tclass==\"file\" " > events/avc/selinux_audited/filter

This adds that we only get tclass=file.

The trace can also have extra properties. Adding the user stack
can be done with
   echo 1 > options/userstacktrace

Now the output will be
         runcon-1365  [003] ....  6960.955530: selinux_audited:
     requested=0x4000000 denied=0x4000000 audited=0x4000000
     result=-13
     scontext=system_u:system_r:cupsd_t:s0-s0:c0.c1023
     tcontext=system_u:object_r:bin_t:s0 tclass=file
          runcon-1365  [003] ....  6960.955560: <user stack trace>
 =>  <00007f325b4ce45b>
 =>  <00005607093efa57>

Signed-off-by: Peter Enderborg <peter.enderborg@sony.com>
Reviewed-by: Thiébaud Weksteen <tweek@google.com>
Acked-by: Stephen Smalley <stephen.smalley.work@gmail.com>
Signed-off-by: Paul Moore <paul@paul-moore.com>
This commit is contained in:
Peter Enderborg 2020-08-21 16:08:22 +02:00 committed by Paul Moore
parent dd8166212d
commit 30969bc8e0
2 changed files with 41 additions and 23 deletions
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36
include/trace/events/avc.h
View file

@ -1,6 +1,7 @@
/* SPDX-License-Identifier: GPL-2.0 */
/*
* Author: Thiébaud Weksteen <tweek@google.com>
* Authors: Thiébaud Weksteen <tweek@google.com>
* Peter Enderborg <Peter.Enderborg@sony.com>
*/
#undef TRACE_SYSTEM
#define TRACE_SYSTEM avc
@ -12,23 +13,38 @@
TRACE_EVENT(selinux_audited,
TP_PROTO(struct selinux_audit_data *sad),
TP_PROTO(struct selinux_audit_data *sad,
char *scontext,
char *tcontext,
const char *tclass
),
TP_ARGS(sad),
TP_ARGS(sad, scontext, tcontext, tclass),
TP_STRUCT__entry(
__field(unsigned int, tclass)
__field(unsigned int, audited)
__field(u32, requested)
__field(u32, denied)
__field(u32, audited)
__field(int, result)
__string(scontext, scontext)
__string(tcontext, tcontext)
__string(tclass, tclass)
),
TP_fast_assign(
__entry->tclass = sad->tclass;
__entry->audited = sad->audited;
__entry->requested = sad->requested;
__entry->denied = sad->denied;
__entry->audited = sad->audited;
__entry->result = sad->result;
__assign_str(tcontext, tcontext);
__assign_str(scontext, scontext);
__assign_str(tclass, tclass);
),
TP_printk("tclass=%u audited=%x",
__entry->tclass,
__entry->audited)
TP_printk("requested=0x%x denied=0x%x audited=0x%x result=%d scontext=%s tcontext=%s tclass=%s",
__entry->requested, __entry->denied, __entry->audited, __entry->result,
__get_str(scontext), __get_str(tcontext), __get_str(tclass)
)
);
#endif

28
security/selinux/avc.c
View file

@ -705,35 +705,37 @@ static void avc_audit_post_callback(struct audit_buffer *ab, void *a)
{
struct common_audit_data *ad = a;
struct selinux_audit_data *sad = ad->selinux_audit_data;
char *scontext;
char *scontext = NULL;
char *tcontext = NULL;
const char *tclass = NULL;
u32 scontext_len;
u32 tcontext_len;
int rc;
trace_selinux_audited(sad);
rc = security_sid_to_context(sad->state, sad->ssid, &scontext,
&scontext_len);
if (rc)
audit_log_format(ab, " ssid=%d", sad->ssid);
else {
else
audit_log_format(ab, " scontext=%s", scontext);
kfree(scontext);
}
rc = security_sid_to_context(sad->state, sad->tsid, &scontext,
&scontext_len);
rc = security_sid_to_context(sad->state, sad->tsid, &tcontext,
&tcontext_len);
if (rc)
audit_log_format(ab, " tsid=%d", sad->tsid);
else {
audit_log_format(ab, " tcontext=%s", scontext);
kfree(scontext);
}
else
audit_log_format(ab, " tcontext=%s", tcontext);
audit_log_format(ab, " tclass=%s", secclass_map[sad->tclass-1].name);
tclass = secclass_map[sad->tclass-1].name;
audit_log_format(ab, " tclass=%s", tclass);
if (sad->denied)
audit_log_format(ab, " permissive=%u", sad->result ? 0 : 1);
trace_selinux_audited(sad, scontext, tcontext, tclass);
kfree(tcontext);
kfree(scontext);
/* in case of invalid context report also the actual context string */
rc = security_sid_to_context_inval(sad->state, sad->ssid, &scontext,
&scontext_len);