Sycall Rules vs Watch Rules

[Amjad Gabbar]

Hi,

Just wanted to follow up wrt the previous findings and experiments and what
some of your thoughts are on the suggested optimizations.

Regards
Ali

On Tue, Sep 12, 2023 at 4:20 PM Amjad Gabbar <amjadgabbar11 at gmail.com>
wrote:

> So,
>
> Based on this and some experiments I have been performing, I would suggest
> changing how a lot of the FileSystem rules are written and illustrated.
> Ex -
> https://github.com/linux-audit/audit-userspace/blob/master/rules/30-pci-dss-v31.rules#L34-L35
>
> The rule in the repository is
> -a always,exit -F path=/etc/sudoers -F perm=wa -F
> key=10.2.2-priv-config-changes
>
> My suggestion is to instead change the rule based on the permissions
> defined. The above rule would change to the following based on the kernel
> being used.
> -a always,exit -S <list of syscalls in audit_write.h and audit_read.h
> +open,openat> -F path=/etc/sudoers -F perm=wa -F
> key=10.2.2-priv-config-changes
>
> This is higher performance because we are limiting the syscalls instead of
> making use of -S all which has more paths of evaluation for each and every
> syscall.
>
> Same thing for watches. Watches are inherently -S all rules which are very
> performance intensive.
>
> https://github.com/linux-audit/audit-userspace/blob/1482cec74f2d9472f81dd4f0533484bd0c26decd/lib/libaudit.c#L805
>
> Ideally we should limit the syscalls based on the permissions being used.
>
> I have implemented the same in my environment rules and have noticed a
> massive performance difference with no difference in the events being
> logged since we anyways filter eventually based on the permissions.
>
> Let me know what you all think.
>
> Ali Adnan.
>
>
>
>
>
> On Wed, Sep 6, 2023 at 2:58 PM Richard Guy Briggs <rgb at redhat.com> wrote:
>
>> On 2023-09-06 10:56, Amjad Gabbar wrote:
>> > Hi,
>> >
>> > I have done some analysis and digging into how both the watch rules and
>> > syscall rules are translated.
>> >
>> > From my understanding, in terms of logging, both the below rules are
>> > similar. There is no difference in either of the rules.
>> >
>> > 1. -w /etc -p wa -k ETC_WATCH
>>
>> They are similar in this case.
>> -w behaves differently depending on the existance of the watched entity
>> and the presence of a trailing "/".  This is why the form above is
>> deprecated.
>>
>> > 2. -a always,exit -F arch=b64 -S <all syscalls part of the write and
>> attr
>> > classes> -F dir=/etc  -F perm=wa -k ETC_WATCH
>> >
>> > The write and attr classes consist of syscalls in
>> > “include/asm-generic/audit_*.h“.
>> >
>> >  The perm flag is needed in the second case for including open/openat
>> > syscalls which are not a part of the write and attr syscall list.
>> >
>> > I'd like to verify if what I mentioned earlier is accurate, and I have
>> an
>> > additional point but depends on whether this is accurate.
>> >
>> > Ali
>>
>> - RGB
>>
>> --
>> Richard Guy Briggs <rgb at redhat.com>
>> Sr. S/W Engineer, Kernel Security, Base Operating Systems
>> Remote, Ottawa, Red Hat Canada
>> Upstream IRC: SunRaycer
>> Voice: +1.613.860 2354 SMS: +1.613.518.6570
>>
>>
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