[Bro-Dev] [JIRA] (BIT-1298) IP_Hdr pointer do not propagate from udp to child analyzers via DeliverPacket method causing a segfault

Jon Siwek (JIRA) jira at bro-tracker.atlassian.net
Wed Dec 10 09:28:00 PST 2014

    [ https://bro-tracker.atlassian.net/browse/BIT-1298?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=19207#comment-19207 ] 

Jon Siwek commented on BIT-1298:

Thanks, I see what's happening now: the process for attaching analyzers via signature matches will buffer packet contents (excluding IP header) until a signature matches and then later replay those packets for analysis.  Since it didn't save the IP header while buffering, those DeliverPacket calls which use replayed content end up with a null IP_Hdr*.

I can see what it takes to fix that, but from your earlier description, you may be able to get the information you were looking for from a different place, e.g.:

diff --git a/src/analyzer/protocol/ntp/NTP.cc b/src/analyzer/protocol/ntp/NTP.cc
index 5778da9..0ba5b3f 100644
--- a/src/analyzer/protocol/ntp/NTP.cc
+++ b/src/analyzer/protocol/ntp/NTP.cc
@@ -27,6 +27,9 @@ void NTP_Analyzer::Done()
 void NTP_Analyzer::DeliverPacket(int len, const u_char* data, bool is_orig, uint64 seq, const IP_Hdr* ip, int caplen)
+       printf("%s:%d\n",
+              Conn()->OrigAddr().AsString().c_str(),
+              ntohs(Conn()->OrigPort()));
        Analyzer::DeliverPacket(len, data, is_orig, seq, ip, caplen);
        // Actually we could just get rid of the Request/Reply and simply use

> IP_Hdr pointer do not propagate from udp to child analyzers via DeliverPacket method causing a segfault
> -------------------------------------------------------------------------------------------------------
>                 Key: BIT-1298
>                 URL: https://bro-tracker.atlassian.net/browse/BIT-1298
>             Project: Bro Issue Tracker
>          Issue Type: Problem
>          Components: Bro
>    Affects Versions: 2.3
>         Environment: Debian
>            Reporter: Eric Asselin
>            Priority: High
>              Labels: analyzer
>         Attachments: core.zip, ntp-synchronized.pcap
> From a child analyzer like NTP, the IP_Hdr pointer in the DeliverPacket method is empty and unusable causing a segmentation fault as soon as you try to access it.
> To recreate the bug, just add an "assert(ip)" inside the DeliverPacket method of a UDP child analyzer and the execution will fail (instead of the segmentation fault).

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