need rules help
I searched the list for an example but see nothing applicable. I need to be able to exclude the following event example:
node=jcdx type=PATH msg=audit(07/20/2009 00:00:16.469:24295) : item=0 name=/var/opt/jcdx/tracks/mltrackdb/AcousticTracks.inst/040fd238ede9dfbbc19e012c7633836f/AcousticTracks node=jcdx type=CWD msg=audit(07/20/2009 00:00:16.469:24295) : cwd=/
node=jcdx type=SYSCALL msg=audit(07/20/2009 00:00:16.469:24295) :
arch=i386 syscall=stat64 success=no exit=-13(Permission denied)
a0=8813598 a1=ffdfed24 a2=c91ff4 a3=ffdfee5c items=1 ppid=1 pid=2747
auid=unset uid=root gid=unknown(450) euid=root suid=root fsuid=root
egid=unknown(450) sgid=unknown(450) fsgid=unknown(450) tty=(none)
ses=4294967295 comm=mtdb exe=/opt/jcdx/sbin/mtdb subj=system_u:system_r:jcdx_mtdb_t:s0-s6:c0.c511 key=(null)
node=jcdx type=AVC msg=audit(07/20/2009 00:00:16.469:24295) : avc:
denied { search } for pid=2747 comm=mtdb
name=040fd238ede9dfbbc19e012c7633836f dev=dm-0 ino=71632 scontext=system_u:system_r:jcdx_mtdb_t:s0-s6:c0.c511 tcontext=system_u:object_r:jcdx_stdb_var_t:s15:c0.c1023 tclass=dir
I thought that the following would work:
-a never,exit -F subj_type=jcdx_mtdb_t -F obj_type=jcdx_stdb_var_t
but it doesn't stop the event from getting into the log.
I saw Steve's suggestion back in January about using the exclude rule, but that one says "only msgtype field works with exclude filter", so I cannot include any other "-F" options.
Any ideas?
Thx,
LCB.
Signature · 2 lines
LC (Lenny) Bruzenak [email protected]
Re: need rules help - solved
Quoted 3 lines · LC Bruzenak
I thought that the following would work:
-a never,exit -F subj_type=jcdx_mtdb_t -F obj_type=jcdx_stdb_var_t
Sorry for the false alarm. This one is operator error (at least I think it is; will retest better, so far it appears to work as advertised).
I realized I had a rule to audit that event in the list. This one needs the "-A' vice "-a" to ensure it goes to the head of the rule line.
LCB.
Signature · 2 lines
LC (Lenny) Bruzenak [email protected]
Quoted 1 line · LC Bruzenak
On Wed, 2009-08-05 at 21:45 -0500, LC Bruzenak wrote:
OK, I'm back with new evidence of a problem after what I think is correct setup. I put only the subj_type as a comparator even though I want a more restrictive set. the rule was set with the "-A" flag.
* My rules start with (use "auditctl -l"):
LIST_RULES: entry,always arch=3221225534 (0xc000003e) syscall=mknod,mknodatLIST_RULES: entry,always arch=3221225534 (0xc000003e) syscall=mount,umount2LIST_RULES: exit,never subj_type=jcdx_mtdb_t syscall=all
...
* I note the date:
Thu Aug 6 20:36:31 UTC 2009
* I search again later (using ausearch) and find:
node=jcdx type=PATH msg=audit(08/06/2009 20:42:20.726:21672) : item=0 name=/var/opt/jcdx/tracks/mltrackdb/PlatformTracks.inst/040fd238ede9dfbbc19e012c7633836f/PlatformTracks node=jcdx type=CWD msg=audit(08/06/2009 20:42:20.726:21672) : cwd=/
node=jcdx type=SYSCALL msg=audit(08/06/2009 20:42:20.726:21672) :
arch=i386 syscall=stat64 success=no exit=-2(No such file or directory)
a0=9a4ea40 a1=ffc93644 a2=d2aff4 a3=ffc9377c items=1 ppid=1 pid=23599
auid=root uid=root gid=jcdx euid=root suid=root fsuid=root egid=jcdx
sgid=jcdx fsgid=jcdx tty=(none) ses=8 comm=mtdb exe=/opt/jcdx/sbin/mtdb subj=system_u:system_r:jcdx_mtdb_t:s0-s6:c0.c511 key=(null)
node=jcdx type=AVC msg=audit(08/06/2009 20:42:20.726:21672) : avc:
denied { search } for pid=23599 comm=mtdb
name=040fd238ede9dfbbc19e012c7633836f dev=dm-0 ino=269567 scontext=system_u:system_r:jcdx_mtdb_t:s0-s6:c0.c511 tcontext=system_u:object_r:jcdx_stdb_var_t:s15:c0.c1023 tclass=dir
So it appears that the "never" rule is not firing...right? I'm not sure if the rule applies to only the info in the "type=syscall" line. Really I want to compare against the specific scontext/tcontext pair in the "type=AVC" line.
Thanks in advance,
LCB.
Signature · 2 lines
LC (Lenny) Bruzenak [email protected]
On Thu, 2009-08-06 at 16:17 -0500, LC Bruzenak wrote:
...
Quoted 15 lines
* My rules start with (use "auditctl -l"):
LIST_RULES: entry,always arch=3221225534 (0xc000003e) syscall=mknod,mknodatLIST_RULES: entry,always arch=3221225534 (0xc000003e) syscall=mount,umount2LIST_RULES: exit,never subj_type=jcdx_mtdb_t syscall=all
...* I note the date:
Thu Aug 6 20:36:31 UTC 2009* I search again later (using ausearch) and find:
Quoted 15 lines
node=jcdx type=PATH msg=audit(08/06/2009 20:42:20.726:21672) : item=0 name=/var/opt/jcdx/tracks/mltrackdb/PlatformTracks.inst/040fd238ede9dfbbc19e012c7633836f/PlatformTracks node=jcdx type=CWD msg=audit(08/06/2009 20:42:20.726:21672) : cwd=/
node=jcdx type=SYSCALL msg=audit(08/06/2009 20:42:20.726:21672) :
arch=i386 syscall=stat64 success=no exit=-2(No such file or directory)
a0=9a4ea40 a1=ffc93644 a2=d2aff4 a3=ffc9377c items=1 ppid=1 pid=23599
auid=root uid=root gid=jcdx euid=root suid=root fsuid=root egid=jcdx
sgid=jcdx fsgid=jcdx tty=(none) ses=8 comm=mtdb exe=/opt/jcdx/sbin/mtdb subj=system_u:system_r:jcdx_mtdb_t:s0-s6:c0.c511 key=(null)
node=jcdx type=AVC msg=audit(08/06/2009 20:42:20.726:21672) : avc:
denied { search } for pid=23599 comm=mtdb
name=040fd238ede9dfbbc19e012c7633836f dev=dm-0 ino=269567 scontext=system_u:system_r:jcdx_mtdb_t:s0-s6:c0.c511 tcontext=system_u:object_r:jcdx_stdb_var_t:s15:c0.c1023 tclass=dir
I guess this is a kernel issue?
I'm using F10 2.6.29.6-93
Thx,
LCB.
Signature · 2 lines
LC (Lenny) Bruzenak [email protected]
Quoted 1 line · LC Bruzenak
So it appears that the "never" rule is not firing...right?
No, its actually something else
Quoted 3 lines
I'm not sure if the rule applies to only the info in the "type=syscall" line. Really I want to compare against the specific scontext/tcontext pair in the "type=AVC" line.
The issue is that SE Linux AVCs travel a different path. When an AVC denial occurs and there is not a dontaudit associated with it, it sends the event straight to the netlink queue. To suppress an AVC, you would need to make a change to SE Linux policy. The SE Linux folks wanted to make sure there was no way to suppress an AVC without explicitly stating so in policy.
-Steve
Quoted 10 lines · Steve Grubb
Quoted 1 line · LC Bruzenak
So it appears that the "never" rule is not firing...right?
No, its actually something else
Quoted 3 lines
I'm not sure if the rule applies to only the info in the "type=syscall" line. Really I want to compare against the specific scontext/tcontext pair in the "type=AVC" line.
Quoted 7 lines
The issue is that SE Linux AVCs travel a different path. When an AVC denial occurs and there is not a dontaudit associated with it, it sends the event straight to the netlink queue. To suppress an AVC, you would need to make a change to SE Linux policy. The SE Linux folks wanted to make sure there was no way to suppress an AVC without explicitly stating so in policy.
-Steve
Bummer. But thanks for the explanation; that makes sense...sort of. Does the "exclude" rule then work for msgtype=AVC (as the manpage says)? If so, seems like a broad stroke is allowed whereas detailed exclusion isn't.
I realize this may be out of your hands, but it might have implications for event aggregation as this feature matures. At the event generation level, this might be desired behavior whereas the collecting machine might not want this detail.
At some point, would it be possible to instantiate filters at either the sending side (audisp-remote) or the receiving side (auditd) to narrow the event collection?
For SElinux then, the "never" flag seems to me almost useless. The vast majority of events I see (YMMV) are either those I explicitly specify in the rules, or else AVCs; e.g.:
[root@audit ~]# aureport -ts today -e -i --summary
Event Summary Report
======================
total type
======================
23851 AVC
121 SYSCALL
60 CRED_DISP 60 USER_END 59 CRED_ACQ 59 USER_ACCT 59 LOGIN 59 USER_START 18 TRUSTED_APP 2 USER_ROLE_CHANGE 1 DAEMON_RESUME 1 CRED_REFR 1 USER_LOGIN 1 USER_AUTH
Thx,
LCB.
Signature · 2 lines
LC (Lenny) Bruzenak [email protected]
Quoted 11 lines · LC Bruzenak
Quoted 6 lines
The issue is that SE Linux AVCs travel a different path. When an AVC denial occurs and there is not a dontaudit associated with it, it sends the event straight to the netlink queue. To suppress an AVC, you would need to make a change to SE Linux policy. The SE Linux folks wanted to make sure there was no way to suppress an AVC without explicitly stating so in policy.
Bummer. But thanks for the explanation; that makes sense...sort of. Does the "exclude" rule then work for msgtype=AVC (as the manpage says)? If so, seems like a broad stroke is allowed whereas detailed exclusion isn't.
Did some more digging on this and found I missed a line of code.
http://lxr.linux.no/linux+v2.6.30.4/kernel/audit.c#L1167
When audit_log_start is called to create an AVC, it calls audit_filter_type() which is the exclude filter.
http://lxr.linux.no/linux+v2.6.30.4/kernel/auditfilter.c#L1743
At line 1757, you can see that it only cares about the event type field. It does not check any other fields that you might have in the rule such as subjects. Originally there was some discussion about not allowing the audit system to suppress AVC's since correcting policy is really the best way to go.
So, I think yes you can suppress AVC's. But its all AVC's and not any particular one. It seems like it would be trivial to add some more checking to the type filter to better tune what is being thrown away.
-Steve
Quoted 20 lines · Steve Grubb
Quoted 11 lines · LC Bruzenak
Quoted 6 lines
The issue is that SE Linux AVCs travel a different path. When an AVC denial occurs and there is not a dontaudit associated with it, it sends the event straight to the netlink queue. To suppress an AVC, you would need to make a change to SE Linux policy. The SE Linux folks wanted to make sure there was no way to suppress an AVC without explicitly stating so in policy.
Bummer. But thanks for the explanation; that makes sense...sort of. Does the "exclude" rule then work for msgtype=AVC (as the manpage says)? If so, seems like a broad stroke is allowed whereas detailed exclusion isn't.
Did some more digging on this and found I missed a line of code.
http://lxr.linux.no/linux+v2.6.30.4/kernel/audit.c#L1167
When
audit_log_startis called to create an AVC, it callsaudit_filter_type()which is the exclude filter.
Quoted 6 lines
http://lxr.linux.no/linux+v2.6.30.4/kernel/auditfilter.c#L1743
At line 1757, you can see that it only cares about the event type field. It does not check any other fields that you might have in the rule such as subjects. Originally there was some discussion about not allowing the audit system to suppress AVC's since correcting policy is really the best way to go.
It may be the best way to go in theory, but in practice, IIUC, the policy rules are not granular enough to specify what the audit rules potentially can.
Also I still think my aggregation-filter ideas have merit eventually and policy won't help this.
Quoted 4 lines
So, I think yes you can suppress AVC's. But its all AVC's and not any particular one. It seems like it would be trivial to add some more checking to the type filter to better tune what is being thrown away.
This would be a huge help to me; I think others would find it useful also. I don't see it as a lesser security stance; there is precedence in legacy systems in the field where this behavior is SOP (although not as elegant as the linux audit rules).
Ideally the complete scontext/tcontext fields (incl. level) in AVC lines are would be what should be filterable.
Thanks for the time/effort to look into this Steve; I really appreciate it!
LCB.
Signature · 2 lines
LC (Lenny) Bruzenak [email protected]