On 10/23/2013 01:59 AM, Richard Guy Briggs wrote:
> On Mon, Oct 21, 2013 at 04:01:40PM +0800, Gao feng wrote:
>> As the man page of auditctl said:
>> "
>> -b backlog
>> Set max number of outstanding audit buffers allowed (Kernel
>> Default=64)
>> If all buffers are full, the failure flag is consulted by the
>> kernel
>> for action.
>> "
>>
>> So if audit_backlog_limit is zero, it means no audit buffer
>> should be allocated.
>
> Which sounds the same as audit=0 on the kernel boot line or "auditctl -e 0"
> to disable it. This is redundant. I would suggest instead that it
> would be more useful to have backlog set to zero mean unlimited (well,
> limited by system RAM). This can be dangerous, but that can be
> warned in the manpage. So, to accomplish that, a minor change is
> needed in the audit_hold_skb() funciton:
>
> diff --git a/kernel/audit.c b/kernel/audit.c
> @@ -355,7 +355,8 @@ static int audit_set_failure(int state)
> static void audit_hold_skb(struct sk_buff *skb)
> {
> if (audit_default &&
> - skb_queue_len(&audit_skb_hold_queue) < audit_backlog_limit)
> + (!audit_backlog_limit ||
> + skb_queue_len(&audit_skb_hold_queue) < audit_backlog_limit))
> skb_queue_tail(&audit_skb_hold_queue, skb);
> else
> kfree_skb(skb);
>
> And here is what I would propose for the corresponding userspace mod:
>
> diff --git a/trunk/docs/auditctl.8 b/trunk/docs/auditctl.8
> @@ -8,7 +8,7 @@ The \fBauditctl\fP program is used to control the behavior,
> get status, and add
> .SH OPTIONS
> .TP
> .BI \-b\ backlog
> -Set max number of outstanding audit buffers allowed (Kernel Default=64) If
> all buffers are full, the failure flag is consulted by the kernel for action.
> +Set max number of outstanding audit buffers allowed (Kernel Default=64) If
> all buffers are full, the failure flag is consulted by the kernel for action.
> Setting this to "0" (which is dangerous) implies an unlimited queue, limited
> only by system resources.
> .TP
> \fB\-e\fP [\fB0\fP..\fB2\fP]
> Set enabled flag. When \fB0\fP is passed, this can be used to temporarily
> disable auditing. When \fB1\fP is passed as an argument, it will enable
> auditing. To lock the audit configuration so that it can't be changed, pass a
> \fB2\fP as the argument. Locking the configuration is intended to be the last
> command in audit.rules for anyone wishing this feature to be active. Any
> attempt to change the configuration in this mode will be audited and denied.
> The configuration can only be changed by rebooting the machine.
> diff --git a/trunk/src/auditctl.c b/trunk/src/auditctl.c
> @@ -107,7 +107,7 @@ static void usage(void)
> " -a <l,a> Append rule to end of <l>ist with <a>ction\n"
> " -A <l,a> Add rule at beginning of <l>ist with
> <a>ction\n"
> " -b <backlog> Set max number of outstanding audit buffers\n"
> - " allowed Default=64\n"
> + " allowed. Default=64 Unlimited=0(dangerous)\n"
> " -c Continue through errors in rules\n"
> " -C f=f Compare collected fields if available:\n"
> " Field name, operator(=,!=), field name\n"
>
>
> Does this sound like a reasonable change?
>
Yes, it's reasonable, I'm ok with this change, just like audit_rate_limit,
zero means unlimited. And it's better to change the comments of
audit_backlog_limit
in kernel.
Thanks.
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