[Snort-devel] [PATCHES] Fixes for daq_nfq

Russ Combs rcombs at ...402...
Tue Nov 2 16:08:36 EDT 2010

On Mon, Oct 25, 2010 at 5:52 PM, Russ Combs <rcombs at ...402...> wrote:

> Thanks for chipping in.  We've already got some changes queued up.  I'll
> take a look at your patch and get back to you.
> Russ
> On Mon, Oct 25, 2010 at 5:18 PM, Kelvie Wong <kwong at ...3121...> wrote:
>> Attached is a patch that fixes a couple of issues (I think they are
>> issues,
>> anyways...) we have found in the NFQ DAQ module in Snort 2.9.0.
>> nfq_get_timestamp (for us) often returns -1, trying to tell us that it
>> does
>> not have a timestamp for this packet, and the first part of this patch
>> just
>> uses the current time when writing the packet header.  Many parts of snort
>> seem to depend on having a valid timestamp in the packet header, so this
>> would
>> definitely break it.
Too bad NFQ is so buggy.  Any idea when this fails and when not?  Is it
certain traffic?

If this happens always or never, for a given run of Snort, the patch is
reasonable.  If it is every other packet, we may be better off just adding
the smallest delta possible to the timestamp to keep them sequenced.

>> The second part of the patch removes the return statement from the packet
>> handling loop inside the NFQ DAQ -- under certain conditions,
>> nfq_handle_packet will break and return early (before calling the
>> callback);
>> this causes snort to either freeze or exit, both undesirable outcomes,
>> especially when Snort is being used in inline mode.
The freeze scenario should be eliminated with daq 0.3.  Can you verify that?

The early exit is a little different.  Does this indicate a permanent
error?  Can you elaborate on the conditions?

The errors were presumbed permanent and Snort exits to avoid consuming
excessive resources.

>> If any of these changes are terribly shortsighted or just plain wrong,
>> please
>> let me know.  I haven't delved that deep into the Snort code yet.
>> --
>> Kelvie Wong
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