Package: python3-scapy Version: 2.4.4-4 Tags: patch When conf.use_pcap is set, the function sr() does not select proper outgoing interfaces, so it gets zero answers.
In the following example, the proper interface for the network 192.168.168.0/24 is veth0. However, sr() sends ICMP packets to the default inteface 'ens3' when conf.use_pcap is set: -----BEGIN CLI----- >>> conf.route Network Netmask Gateway Iface Output IP Metric 0.0.0.0 0.0.0.0 10.0.2.2 ens3 10.0.2.15 0 10.0.2.0 255.255.255.0 0.0.0.0 ens3 10.0.2.15 0 127.0.0.0 255.0.0.0 0.0.0.0 lo 127.0.0.1 1 192.168.168.0 255.255.255.0 0.0.0.0 veth0 192.168.168.1 0 >>> conf.iface 'ens3' >>> conf.use_pcap True >>> sr(IP(dst='192.168.168.2')/ICMP(seq=(1,1000)), timeout=1) Begin emission: Finished sending 1000 packets. ....................................................................... ....................................................................... ...................................................... Received 196 packets, got 0 answers, remaining 1000 packets (<Results: TCP:0 UDP:0 ICMP:0 Other:0>, <Unanswered: TCP:0 UDP:0 ICMP:1000 Other:0>) # tcpdump -ni ens3 -c10 icmp tcpdump: verbose output suppressed, use -v[v]... for full protocol decode listening on ens3, link-type EN10MB (Ethernet), snapshot length 262144 bytes 22:22:28.165580 IP 192.168.168.1 > 192.168.168.2: ICMP echo request, id 0, seq 1, length 8 22:22:28.167091 IP 192.168.168.1 > 192.168.168.2: ICMP echo request, id 0, seq 2, length 8 22:22:28.168075 IP 192.168.168.1 > 192.168.168.2: ICMP echo request, id 0, seq 3, length 8 22:22:28.169068 IP 192.168.168.1 > 192.168.168.2: ICMP echo request, id 0, seq 4, length 8 22:22:28.169988 IP 192.168.168.1 > 192.168.168.2: ICMP echo request, id 0, seq 5, length 8 22:22:28.170900 IP 192.168.168.1 > 192.168.168.2: ICMP echo request, id 0, seq 6, length 8 22:22:28.171933 IP 192.168.168.1 > 192.168.168.2: ICMP echo request, id 0, seq 7, length 8 22:22:28.172917 IP 192.168.168.1 > 192.168.168.2: ICMP echo request, id 0, seq 8, length 8 22:22:28.174020 IP 192.168.168.1 > 192.168.168.2: ICMP echo request, id 0, seq 9, length 8 22:22:28.174913 IP 192.168.168.1 > 192.168.168.2: ICMP echo request, id 0, seq 10, length 8 10 packets captured 94 packets received by filter 0 packets dropped by kernel -----END CLI----- The problem gets resolved when the proper 'iface' is set globally or supplied to the sr() function: -----BEGIN CLI----- >>> conf.iface 'ens3' >>> sr(IP(dst='192.168.168.2')/ICMP(seq=(1,1000)), timeout=1, iface='veth0') Begin emission: Finished sending 1000 packets. *********************************************************************** *********************************************************************** *********************************************************************** *********************************************************************** *********************************************************************** *********************************************************************** *********************************************************************** *********************************************************************** *********************************************************************** *********************************************************************** *********************************************************************** *********************************************************************** *********************************************************************** *********************************************************************** ****** Received 1000 packets, got 1000 answers, remaining 0 packets (<Results: TCP:0 UDP:0 ICMP:1000 Other:0>, <Unanswered: TCP:0 UDP:0 ICMP:0 Other:0>) >>> conf.iface = 'veth0' >>> conf.iface 'veth0' >>> sr(IP(dst='192.168.168.2')/ICMP(seq=(1,1000)), timeout=1) Begin emission: Finished sending 1000 packets. *********************************************************************** *********************************************************************** *********************************************************************** *********************************************************************** *********************************************************************** *********************************************************************** *********************************************************************** *********************************************************************** *********************************************************************** *********************************************************************** *********************************************************************** *********************************************************************** *********************************************************************** *********************************************************************** ****** Received 1000 packets, got 1000 answers, remaining 0 packets (<Results: TCP:0 UDP:0 ICMP:1000 Other:0>, <Unanswered: TCP:0 UDP:0 ICMP:0 Other:0>) -----END CLI----- The problem was fixed in the upstream by calling the missing function _interface_selection() as part of general sr1() cleanup [1] for the reported issue 3583 [2]. Considering that the upstream commit 50e867aa9ee9061e79890e5f535eb5ccb6e2a7f3 does a bit more than just fixing the sr() function, probably just adding the missing function in sr() might be the safest way to backport the fix to 2.4.4. I have attached a debdiff patch that basically adds the missing function without refactoring the related sr1() function. Below is the result of using the updated package: -----BEGIN CLI---- # dpkg -s python3-scapy | grep Ver Version: 2.4.4-5 >>> conf.use_pcap True >>> conf.iface 'ens3' >>> sr(IP(dst='192.168.168.2')/ICMP(seq=(1,1000)), timeout=1) Begin emission: Finished sending 1000 packets. *********************************************************************** *********************************************************************** *********************************************************************** *********************************************************************** *********************************************************************** *********************************************************************** *********************************************************************** *********************************************************************** *********************************************************************** *********************************************************************** *********************************************************************** *********************************************************************** *********************************************************************** *********************************************************************** ****** Received 1000 packets, got 1000 answers, remaining 0 packets (<Results: TCP:0 UDP:0 ICMP:1000 Other:0>, <Unanswered: TCP:0 UDP:0 ICMP:0 Other:0>) -----END CLI---- To replicate the network configuration I used for the test, the following commands can be used: -----BEGIN CLI---- ip net add scapy ip link add type veth ip link set veth1 netns scapy ip link set veth0 up ip addr add 192.168.168.1/24 dev veth0 ip netns exec scapy ip link set lo up ip netns exec scapy ip link set veth1 up ip netns exec scapy ip addr add 192.168.168.2/24 dev veth1 -----END CLI---- Please note that the requirement to set 'conf.use_pcap' is necessary in my environment to overcome the recently found issue [3] with the native super sockets. Thank you. Regards, Garri [1] https://github.com/secdev/scapy/pull/3610 [2] https://github.com/secdev/scapy/issues/3583 [3] https://github.com/secdev/scapy/issues/4531
diff -Nru scapy-2.4.4/debian/changelog scapy-2.4.4/debian/changelog --- scapy-2.4.4/debian/changelog 2021-01-11 10:40:10.000000000 +0000 +++ scapy-2.4.4/debian/changelog 2024-09-15 21:51:12.000000000 +0000 @@ -1,3 +1,11 @@ +scapy (2.4.4-5) unstable; urgency=medium + + * Non-maintainer upload. + + * Add a patch to fix interface selection in sr() + + -- Garri Djavadyan <g.djavad...@gmail.com> Sun, 15 Sep 2024 21:51:12 +0000 + scapy (2.4.4-4) unstable; urgency=medium * Team upload. diff -Nru scapy-2.4.4/debian/patches/fix-select-iface-in-sr.patch scapy-2.4.4/debian/patches/fix-select-iface-in-sr.patch --- scapy-2.4.4/debian/patches/fix-select-iface-in-sr.patch 1970-01-01 00:00:00.000000000 +0000 +++ scapy-2.4.4/debian/patches/fix-select-iface-in-sr.patch 2024-09-15 21:50:07.000000000 +0000 @@ -0,0 +1,12 @@ +Index: scapy-2.4.4/scapy/sendrecv.py +=================================================================== +--- scapy-2.4.4.orig/scapy/sendrecv.py 2020-09-02 11:26:21.000000000 +0000 ++++ scapy-2.4.4/scapy/sendrecv.py 2024-09-15 21:50:01.563810502 +0000 +@@ -505,6 +505,7 @@ + """ + Send and receive packets at layer 3 + """ ++ iface = _interface_selection(iface, x) + s = conf.L3socket(promisc=promisc, filter=filter, + iface=iface, nofilter=nofilter) + result = sndrcv(s, x, *args, **kargs) diff -Nru scapy-2.4.4/debian/patches/series scapy-2.4.4/debian/patches/series --- scapy-2.4.4/debian/patches/series 2021-01-11 10:40:10.000000000 +0000 +++ scapy-2.4.4/debian/patches/series 2024-09-15 21:49:37.000000000 +0000 @@ -5,3 +5,4 @@ add-support-for-python3.9.patch Fix-find-library-libc-for-python-3.9.patch upstream-42d58d8729.patch +fix-select-iface-in-sr.patch
