Looks like issue in handling active_nodes count in 4.19 kernel .

[Stephen Smalley]

On 12/17/19 10:40 AM, Ravi Kumar Siddojigari wrote:
> Yes  indeed this is a stress test on ARM64 device with multicore  where most of the cores /tasks are stuck  in avc_reclaim_node .
> We still see this issue even after picking the earlier patch " selinux: ensure we cleanup the internal AVC counters on error in avc_insert() commit: d8db60cb23e4"
> Where selinux_state  during issue was as below where all the slots are  NULL and the count was more than threshold.
> Which seem to be calling avc_reclaim_node always and as the all the slots are empty its going for full for- loop with locks and unlock and taking too long .
> Not sure what could make the  slots null , for sure its not due to flush() /Reset(). We think that still we need to call  avc_kill_node  in update_node function .
> Adding the patch below can you please review or correct the following patch .
> 
> 
>    selinux_state = (
>      disabled = FALSE,
>      enforcing = TRUE,
>      checkreqprot = FALSE,
>      initialized = TRUE,
>      policycap = (TRUE, TRUE, TRUE, FALSE, FALSE, TRUE),
>      avc = 0xFFFFFF9BEFF1E890 -> (
>        avc_cache_threshold = 512,  /* <<<<<not configured and its with default*/
>        avc_cache = (
>          slots = ((first = 0x0), (first = 0x0), (first = 0x0), (first = 0x0), (first = 0x0), (first = 0x0), (first = 0x0), (first = 0x0), (first = 0x0), (first = 0x0), (first = 0x0), (first = 0x0), (first   /*<<<< all are NULL */
>          slots_lock = ((rlock = (raw_lock = (val = (counter = 0), locked = 0, pending = 0, locked_pending = 0, tail = 0), magic = 3735899821, owner_cpu = 4294967295, owner = 0xFFFFFFFFFFFFFFFF, dep_map = (key = 0xFFFFFF9BEFF298A8, cla
>          lru_hint = (counter = 616831529),
>          active_nodes = (counter = 547),   /*<<<<< increased more than 512*/
>          latest_notif = 1)),
>      ss = 0xFFFFFF9BEFF2E578)
> 
> 
> --
> In AVC update we don't call avc_node_kill() when avc_xperms_populate()
> fails, resulting in the avc->avc_cache.active_nodes counter having a
> false value.In last patch this changes was missed , so correcting it.
> 
> Change-Id: Ic0298162cc766c0f21be7ab232e259766654dad3
> Signed-off-by: Jaihind Yadav<jaihindyadav at codeaurora.org>
> ---
>   security/selinux/avc.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/security/selinux/avc.c b/security/selinux/avc.c
> index 91d24c2..3d1cff2 100644
> --- a/security/selinux/avc.c
> +++ b/security/selinux/avc.c
> @@ -913,7 +913,7 @@ static int avc_update_node(struct selinux_avc *avc,
>          if (orig->ae.xp_node) {
>                  rc = avc_xperms_populate(node, orig->ae.xp_node);
>                  if (rc) {
> -                       kmem_cache_free(avc_node_cachep, node);
> +                       avc_node_kill(avc, node);
>                          goto out_unlock;
>                  }
>          }
> --

That looks correct to me; I guess that one got missed by the prior fix.
Still not sure how your AVC got into that state though...

Acked-by: Stephen Smalley <sds at tycho.nsa.gov>