Comments on: Creating a Netfilter kernel module which filters UDP packets http://www.paulkiddie.com/2009/11/creating-a-netfilter-kernel-module-which-filters-udp-packets/ Mainly coding... Sun, 15 Aug 2010 18:23:38 +0000 http://wordpress.org/?v=abc hourly 1 By: prashant kapoor http://www.paulkiddie.com/2009/11/creating-a-netfilter-kernel-module-which-filters-udp-packets/comment-page-1/#comment-718 prashant kapoor Fri, 11 Jun 2010 15:43:06 +0000 http://www.paulkiddie.com/?p=186#comment-718 Hi Paul Congrats , I think you have the best tutorial explaining netfilter kernel module. If we make drastic changes to the packet that the packet is not at all recognizable and we want to send the packets back to the pre-routing, do we have to do something special? Hi Paul

Congrats , I think you have the best tutorial explaining netfilter kernel module.

If we make drastic changes to the packet that the packet is not at all recognizable and we want to send the packets back to the pre-routing, do we have to do something special?

]]> By: jashmi http://www.paulkiddie.com/2009/11/creating-a-netfilter-kernel-module-which-filters-udp-packets/comment-page-1/#comment-649 jashmi Tue, 20 Apr 2010 16:08:36 +0000 http://www.paulkiddie.com/?p=186#comment-649 Hi paul, I am a beginer .I tried inserting this module and module insertion was successfull.But wen i sent traffic , system hangs.Any suggestion on what can be done for this problem.I changed NF_IP_PRE_ROUTING as NF_INET_PRE_ROUTING. Hi paul,
I am a beginer .I tried inserting this module and module insertion was successfull.But wen i sent traffic , system hangs.Any suggestion on what can be done for this problem.I changed NF_IP_PRE_ROUTING as NF_INET_PRE_ROUTING.

]]> By: Ben Evans http://www.paulkiddie.com/2009/11/creating-a-netfilter-kernel-module-which-filters-udp-packets/comment-page-1/#comment-316 Ben Evans Mon, 25 Jan 2010 18:16:19 +0000 http://www.paulkiddie.com/?p=186#comment-316 Hi Paul, Thanks for this series of articles - they've been very useful so far. One thing, is that neither this one nor the previous seem to work on Ubuntu 9 (2.6.28-16 kernel). The errors look like this: bje@bje-desktop:~/projects/netfilter-test$ make make -C /lib/modules/2.6.28-16-generic/build SUBDIRS=/home/bje/projects/netfilter-test modules make[1]: Entering directory `/usr/src/linux-headers-2.6.28-16-generic' CC [M] /home/bje/projects/netfilter-test/nfudp.o /home/bje/projects/netfilter-test/nfudp.c: In function ‘init_module’: /home/bje/projects/netfilter-test/nfudp.c:42: warning: assignment from incompatible pointer type /home/bje/projects/netfilter-test/nfudp.c:43: error: ‘NF_IP_PRE_ROUTING’ undeclared (first use in this function) /home/bje/projects/netfilter-test/nfudp.c:43: error: (Each undeclared identifier is reported only once /home/bje/projects/netfilter-test/nfudp.c:43: error: for each function it appears in.) make[2]: *** [/home/bje/projects/netfilter-test/nfudp.o] Error 1 make[1]: *** [_module_/home/bje/projects/netfilter-test] Error 2 make[1]: Leaving directory `/usr/src/linux-headers-2.6.28-16-generic' make: *** [default] Error 2 Examining linux/netfilter_ipv4.h seems to indicate that an #ifndef __KERNEL__ now extends further than it used to and is preventing NF_IP_PRE_ROUTING from being visible to the module. Something similar is suggested by: http://markmail.org/message/kvzvzc32v3htduin#query:netfilter_ipv4.h%20changes%20kernel+page:1+mid:chddq75k2cxjzuqr+state:results Any thoughts as to what needs to be done to change these examples to work with a 2.6.28-16 or thereabouts kernel? Hi Paul,

Thanks for this series of articles – they’ve been very useful so far.

One thing, is that neither this one nor the previous seem to work on Ubuntu 9 (2.6.28-16 kernel). The errors look like this:

bje@bje-desktop:~/projects/netfilter-test$ make
make -C /lib/modules/2.6.28-16-generic/build SUBDIRS=/home/bje/projects/netfilter-test modules
make[1]: Entering directory `/usr/src/linux-headers-2.6.28-16-generic’
CC [M] /home/bje/projects/netfilter-test/nfudp.o
/home/bje/projects/netfilter-test/nfudp.c: In function ‘init_module’:
/home/bje/projects/netfilter-test/nfudp.c:42: warning: assignment from incompatible pointer type
/home/bje/projects/netfilter-test/nfudp.c:43: error: ‘NF_IP_PRE_ROUTING’ undeclared (first use in this function)
/home/bje/projects/netfilter-test/nfudp.c:43: error: (Each undeclared identifier is reported only once
/home/bje/projects/netfilter-test/nfudp.c:43: error: for each function it appears in.)
make[2]: *** [/home/bje/projects/netfilter-test/nfudp.o] Error 1
make[1]: *** [_module_/home/bje/projects/netfilter-test] Error 2
make[1]: Leaving directory `/usr/src/linux-headers-2.6.28-16-generic’
make: *** [default] Error 2

Examining linux/netfilter_ipv4.h seems to indicate that an #ifndef __KERNEL__ now extends further than it used to and is preventing NF_IP_PRE_ROUTING from being visible to the module. Something similar is suggested by:

http://markmail.org/message/kvzvzc32v3htduin#query:netfilter_ipv4.h%20changes%20kernel+page:1+mid:chddq75k2cxjzuqr+state:results

Any thoughts as to what needs to be done to change these examples to work with a 2.6.28-16 or thereabouts kernel?

]]> By: Srudeep K http://www.paulkiddie.com/2009/11/creating-a-netfilter-kernel-module-which-filters-udp-packets/comment-page-1/#comment-145 Srudeep K Mon, 02 Nov 2009 19:35:57 +0000 http://www.paulkiddie.com/?p=186#comment-145 Is there any other way to do it? Is acess to the saddr field of iphdr structure is legal? or is there any other method to access it? Is there any other way to do it? Is acess to the saddr field of iphdr structure is legal? or is there any other method to access it?

]]> By: Srudeep K http://www.paulkiddie.com/2009/11/creating-a-netfilter-kernel-module-which-filters-udp-packets/comment-page-1/#comment-144 Srudeep K Mon, 02 Nov 2009 19:30:44 +0000 http://www.paulkiddie.com/?p=186#comment-144 Hi Paul, Thank you very much for the kind reply. Your second article helped me a lot. I have small doubt, if I want to acess the source and destination address from the ip header of the packet, is there any way to do it? As we are looking for INET protocol family (pf = PF_INET) we should capture all ip packets and all packets should contain source address. With this back ground I have tried using the saddr variable which is in iphdr structure (iphdr->saddr) but it gave me segmentation fault. I am not able to debug this fault, my system just hangs. Hi Paul,
Thank you very much for the kind reply. Your second article helped me a lot. I have small doubt, if I want to acess the source and destination address from the ip header of the packet, is there any way to do it? As we are looking for INET protocol family (pf = PF_INET) we should capture all ip packets and all packets should contain source address. With this back ground I have tried using the saddr variable which is in iphdr structure (iphdr->saddr) but it gave me segmentation fault. I am not able to debug this fault, my system just hangs.

]]> By: Paul Kiddie’s Blog : Creating a “hello world” kernel module in linux http://www.paulkiddie.com/2009/11/creating-a-netfilter-kernel-module-which-filters-udp-packets/comment-page-1/#comment-141 Paul Kiddie’s Blog : Creating a “hello world” kernel module in linux Mon, 02 Nov 2009 12:13:03 +0000 http://www.paulkiddie.com/?p=186#comment-141 [...] Access packet headers within Netfilter hook [...] [...] Access packet headers within Netfilter hook [...]

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