On 12/11/19 9:37 AM, Stephen Smalley wrote:
On 12/9/19 1:30 PM, rsiddoji@xxxxxxxxxxxxxx wrote:
Thanks for quick response , yes it will be helpful if you can raise
the change .
On the second issue in avc_alloc_node we are trying to check the
slot status as active_nodes > 512 ( default )
Where checking the occupancy should be corrected as active_nodes
> 80% of slots occupied or 16*512 or
May be we need to use a different logic .
Are you seeing an actual problem with this in practice, and if so, what
exactly is it that you are seeing and do you have a reproducer?
BTW, on Linux distributions, there is an avcstat(8) utility that can be
used to monitor the AVC statistics, or you can directly read the stats
from the kernel via /sys/fs/selinux/avc/cache_stats
/*@ static struct avc_node *avc_alloc_node(struct selinux_avc *avc) */
if (atomic_inc_return(&avc->avc_cache.active_nodes) >
avc->avc_cache_threshold) // default threshold is 512
avc_reclaim_node(avc);
Regards,
Ravi
-----Original Message-----
From: selinux-owner@xxxxxxxxxxxxxxx <selinux-owner@xxxxxxxxxxxxxxx> On
Behalf Of Stephen Smalley
Sent: Monday, December 9, 2019 11:35 PM
To: rsiddoji@xxxxxxxxxxxxxx; selinux@xxxxxxxxxxxxxxx
Cc: paul@xxxxxxxxxxxxxx; linux-security-module@xxxxxxxxxxxxxxx
Subject: Re: Looks like issue in handling active_nodes count in 4.19
kernel .
On 12/9/19 10:55 AM, rsiddoji@xxxxxxxxxxxxxx wrote:
Hi team ,
Looks like we have issue in handling the "active_nodes" count in the
Selinux - avc.c file.
Where avc_cache.active_nodes increase more than slot array and code
frequency calling of avc_reclaim_node() from avc_alloc_node() ;
Where following are the 2 instance which seem to possible culprits
which are seen on 4.19 kernel . Can you comment if my understand is
wrong.
#1. if we see the active_nodes count is incremented in
avc_alloc_node
(avc) which is called in avc_insert()
Where if the code take failure path on avc_xperms_populate the code
will not decrement this counter .
static struct avc_node *avc_insert(struct selinux_avc *avc,
u32 ssid, u32 tsid, u16 tclass,
struct av_decision *avd,
....
node = avc_alloc_node(avc); //incremented here ....
rc = avc_xperms_populate(node, xp_node); //
possibilities of this getting failure is there .
if (rc) {
kmem_cache_free(avc_node_cachep, node); // but on
failure we are
not decrementing active_nodes ?
return NULL;
}
I think you are correct; we should perhaps be calling avc_node_kill()
here as we do in an earlier error path?
#2. where it looks like the logic on comparing the active_nodes
against avc_cache_threshold seems wired as the count of active nodes
is always going to be
more than 512 will may land in simply removing /calling
avc_reclaim_node frequently much before the slots are full maybe we
are not using cache at best ?
we should be comparing with some high watermark ? or my
understanding wrong ?
/*@ static struct avc_node *avc_alloc_node(struct selinux_avc *avc) */
if (atomic_inc_return(&avc->avc_cache.active_nodes) >
avc->avc_cache_threshold) // default threshold is 512
avc_reclaim_node(avc);
Not entirely sure what you are asking here. avc_reclaim_node() should
reclaim multiple nodes up to AVC_CACHE_RECLAIM. Possibly that should
be configurable via selinuxfs too, and/or calculated from
avc_cache_threshold in some way?
Were you interested in creating a patch to fix the first issue above
or looking to us to do so?
