On Thu, Oct 20, 2016 at 12:07 PM, Paul Moore <[email protected]> wrote:
> On Thu, Oct 20, 2016 at 2:29 PM, Cong Wang <[email protected]> wrote:
>> On Thu, Oct 20, 2016 at 7:58 AM, Stephen Smalley <[email protected]> wrote:
>>> On 10/20/2016 02:52 AM, Cong Wang wrote:
>>>> A kernel warning inside __local_bh_enable_ip() was reported by people
>>>> running SELinux, this is caused due to some SELinux functions
>>>> (indirectly) call peernet2id() with IRQ disabled in process context,
>>>> when we re-enable BH with IRQ disabled kernel complains. Shut up this
>>>> warning by saving IRQ context in peernet2id(), BH is still implicitly
>>>> disabled.
>>>
>>> Not sure this suffices; kill_fasync() -> send_sigio() ->
>>> send_sigio_to_task() -> sigio_perm() -> security_file_send_sigiotask()
>>> -> selinux_file_send_sigiotask() -> ... -> audit_log() -> ... ->
>>> peernet2id()
>>
>> Oh, this is a new one. kill_fasync() is called in IRQ handler, so we actually
>> do multicast in IRQ context.... It makes no sense, netlink multicast could
>> be very expensive if we have many listeners.
>
> I'm sure there are a few others I don't know about, but I believe the
> only commonly used audit multicast listener is systemd.
But user-space is free to listen to this group, right? If so this is just open
for a potential DDOS attack.
>
>> I am Cc'ing Richard who added that multicast in audit_log_end(). It seems
>> not easy to just move the multicast to a workqueue, since the skb is copied
>> from audit_buffer which is freed immediately after that, probably need
>> another
>> queue like audit_skb_queue.
>
> This approach would double the queue size which is something I want to
> avoid. I would suggest sticking with a single queue and dealing with
> the netlink message link fixup and multicast send in the existing
> netlink unicast thread; basically we would just be moving the
> multicast code from audit_log_end() into kauditd_thread(). This is
> the same approach I mentioned earlier off-list.
This is what I did in the follow up patch. I attach the updated version
in this email for you to review, I still can't make selinux-testsuites working
on my Fedora even though I have SELinux=enforcing, anyhow I don't
see any kernel warning in my dmesg at least.
>
> However, that isn't something I want to mess with as a regression fix,
> mostly because I really want to see this regression gone by -rc2 as it
> is making SELinux testing a real pain. If the patch posted at the top
> of this thread isn't a suitable fix, we really should revert the
> original patch.
Since you want to test SELinux anyway, please test the attached one.
Thanks.
diff --git a/kernel/audit.c b/kernel/audit.c
index f1ca116..cdc5a91 100644
--- a/kernel/audit.c
+++ b/kernel/audit.c
@@ -139,6 +139,7 @@ static int audit_freelist_count;
static LIST_HEAD(audit_freelist);
static struct sk_buff_head audit_skb_queue;
+static struct sk_buff_head audit_skb_multicast_queue;
/* queue of skbs to send to auditd when/if it comes back */
static struct sk_buff_head audit_skb_hold_queue;
static struct task_struct *kauditd_task;
@@ -468,7 +469,8 @@ static void kauditd_send_multicast_skb(struct sk_buff *skb,
gfp_t gfp_mask)
if (!copy)
return;
- nlmsg_multicast(sock, copy, 0, AUDIT_NLGRP_READLOG, gfp_mask);
+ skb_queue_tail(&audit_skb_multicast_queue, copy);
+ wake_up_interruptible(&kauditd_wait);
}
/*
@@ -509,6 +511,26 @@ static void flush_hold_queue(void)
consume_skb(skb);
}
+static void flush_multicast_queue(void)
+{
+ struct audit_net *aunet = net_generic(&init_net, audit_net_id);
+ struct sock *sock = aunet->nlsk;
+ struct sk_buff *skb = skb_dequeue(&audit_skb_multicast_queue);
+
+ if (!netlink_has_listeners(sock, AUDIT_NLGRP_READLOG)) {
+ while (skb) {
+ consume_skb(skb);
+ skb = skb_dequeue(&audit_skb_multicast_queue);
+ }
+ return;
+ }
+
+ while (skb) {
+ nlmsg_multicast(sock, skb, 0, AUDIT_NLGRP_READLOG, GFP_KERNEL);
+ skb = skb_dequeue(&audit_skb_multicast_queue);
+ }
+}
+
static int kauditd_thread(void *dummy)
{
set_freezable();
@@ -517,6 +539,8 @@ static int kauditd_thread(void *dummy)
flush_hold_queue();
+ flush_multicast_queue();
+
skb = skb_dequeue(&audit_skb_queue);
if (skb) {
@@ -530,7 +554,8 @@ static int kauditd_thread(void *dummy)
continue;
}
- wait_event_freezable(kauditd_wait,
skb_queue_len(&audit_skb_queue));
+ wait_event_freezable(kauditd_wait,
skb_queue_len(&audit_skb_queue)
+ ||
skb_queue_len(&audit_skb_multicast_queue));
}
return 0;
}
@@ -1197,6 +1222,7 @@ static int __init audit_init(void)
register_pernet_subsys(&audit_net_ops);
skb_queue_head_init(&audit_skb_queue);
+ skb_queue_head_init(&audit_skb_multicast_queue);
skb_queue_head_init(&audit_skb_hold_queue);
audit_initialized = AUDIT_INITIALIZED;
audit_enabled = audit_default;
