Hi Amit thanks again. the last part is still not clear. I want to know how can u send new packets in the kernel the same way libnet does. The idea is that after i have returned NF_STOLEN from inside my hook functions in the kernel modules, i want to queue them toa kernel thread. the thread does processing in its own manner and sends them out using some other mechanism. what is that mechanism?? I hope u are understanding my point.. regds Mayank -----Original Message----- From: aksingh@xxxxxxxxxxx [mailto:aksingh@xxxxxxxxxxx] Sent: Wednesday, June 30, 2004 10:50 AM To: Mayank Kumar; netfilter@xxxxxxxxxxxxxxxxxxx; netfilter-devel@xxxxxxxxxxxxxxxxxxx Subject: Re: FW: injecting new packets into the netfilter Amit Kumar Singh 06/30/2004 10:35 AM To: "Mayank Kumar" <mayank_kumar@xxxxxxxxxxxxxxxxxxxxxxxxxxxx> cc: <netfilter@xxxxxxxxxxxxxxxxxxx>, <netfilter-devel@xxxxxxxxxxxxxxxxxxx> Subject: Re: FW: injecting new packets into the netfilter (Document link: Amit Kumar Singh) hi, pls see inline "Mayank Kumar" <mayank_kumar@xxxxxxxxxxxxxxxxxxxxxxxxxxxx>@lists.netfilter.org on 06/30/2004 10:16:59 AM Sent by: netfilter-admin@xxxxxxxxxxxxxxxxxxx To: Amit Kumar Singh/HSS@HSS cc: <netfilter@xxxxxxxxxxxxxxxxxxx>, <netfilter-devel@xxxxxxxxxxxxxxxxxxx> Subject: FW: injecting new packets into the netfilter Hi Amit i think u missed out my mail so i resending it to you regds Mayank -----Original Message----- From: Mayank Kumar [mailto:mayank_kumar@xxxxxxxxxxxxxxxxxxxxxxxxxxxx] Sent: Tuesday, June 29, 2004 11:49 AM To: aksingh@xxxxxxxxxxx Cc: netfilter@xxxxxxxxxxxxxxxxxxx Subject: RE: injecting new packets into the netfilter Hi Amit thanks for ur prompt replies. firstly from ur replies it seems that 1: Whatever packets that i will construct using libnet or for that matter using ordinary bsd sockets would pass the relevant hooks in the netfilter based on the dest ip address i set. Is this true?? In this case i am constructing the packet completely on my own. >>> yes that is true, see netfilter hooks if you have read about them, catch ANY packet that passes thru the machines IP, be it raw packets that you inject using libnet(they are caught first by IP_LOCAL_OUT .. then they might hit other hooks), oor if they are coming from ethernet or any sort of mac layer(in this case caught first by PRE_ROUTING hook and then by others ) ...>>>> Now what i want to do is steal(NF_STOLEN) packets at specific hooks (generally pre routing) within the netfilter and queue them to a user mode process. The User mode process does some processing and either sends the same packet or completely new and umpteen in number packets at the post routing hook in netfilter(from ur answer using libnet). >>> libnet is just one of the ways, you can use normal BSD sockets, or raw sockets "any" packet that reaches IP wld be caught by the netfilter hooks(provided you have registered your call back functions). For user space queueing, better would be to return an NF_QUEUE, then use inbuilt kernel module ip_queue.o and the user space library libipq. Once you return NF_QUEUE and if ip_queue is already insmoded, your user level applciationthat is doing a ipq_read()(a function call from library libipq), wld get it, then you can play with the packet and return in without problems .. read about libipq for this, if u jave iptables, then doing a make install-devel in the directory where iptables asource is, wld install libipq >>>>>>> >From ur answer it seems quite possible very easily. Correct me if i am wrong here. >>>>> if you understand how ip_queue, libipq and libnet work it shld be fine ;-) >>>>> Also is there any advantage of using libnet over bsd sockets in terms of performance. Is there any other performance optmized way of sending and receiving packets from user to kernel mode?? Does netlink sockets way offer a more optimized way of doing it?? (Sorry for a flurry of questions!!) >>>>> ip_queue the kernel module i talk to and libipq use netlink sockets to tarnsfer packets from kernel space to use space, if you want to transfer new packets from user space to kernel space, i suggested libnet, you can use normal raw sockets, bsd sockets, whatever you wish to >>>>> Now the second part is what if i want to move it all to kernel mode for performance reasons. This means steal packet at pre_routing and then queue them all to a kernel thread which was created using a kernel module. The kernel thread then does some processing on the packets and then sends either the captured packet or completely new packets out through the post routing hook. >>>>>>>> yes it is possible, you can do it in kernel itself, performance wld certainly be better but in that case maintenance/debugging might be a problem, theres a trade off, you can make a kernel module which does all the processing on the packets that netfilter hook functions capture, depends on how complex you want that module to be. >>>>>> ? How can this be achieved?? >>> yes this can be achievded as above >>>> regds Mayank -----Original Message----- From: aksingh@xxxxxxxxxxx [mailto:aksingh@xxxxxxxxxxx] Sent: Tuesday, June 29, 2004 11:21 AM To: Mayank Kumar Cc: netfilter@xxxxxxxxxxxxxxxxxxx Subject: RE: injecting new packets into the netfilter Hi, You want to insert packets within the kernel module thta has netfilter hooks ?, I dont thinkthat is a very good idea, as the packets u send using a libnet application wld be caught at the netfilter hooks, if the application resides on the same pc on which yr kernel module that has hook funcstions resides, then those packets will traverse, local_out, post routing, pre_routing, local_in etc based on their dest ip addresses, any packet coming from ethernet wld traverse pre_routing, then local_in or ip_forward and post_routing ..... Amit "Mayank Kumar" <mayank_kumar@xxxxxxxxxxxxxxxxxxxxxxxxxxxx>@lists.netfilter.org on 06/29/2004 11:15:52 AM Sent by: netfilter-admin@xxxxxxxxxxxxxxxxxxx To: Amit Kumar Singh/HSS@HSS cc: <netfilter@xxxxxxxxxxxxxxxxxxx> Subject: RE: injecting new packets into the netfilter Hi Akash i know of this library. But i want to inject packets at precise hooks in the netfilter. for e.g. i want to inject packets whenever the need arises ,at the fwding hook or the post routing hook. Will the raw packets i send using the libnet get caught at hooks inserted using netfilter at various points. regds Mayank -----Original Message----- From: aksingh@xxxxxxxxxxx [mailto:aksingh@xxxxxxxxxxx] Sent: Tuesday, June 29, 2004 10:49 AM To: Mayank Kumar Cc: netfilter@xxxxxxxxxxxxxxxxxxx Subject: Re: injecting new packets into the netfilter Hi, Try libnet for injecting new packets, you can use raw packets(u inject from userland), libnet provides you with a better interface, but you wld need root permission to use raw sockets. you can get libnet library from packetfactory.net HTH Amit "Mayank Kumar" <mayank_kumar@xxxxxxxxxxxxxxxxxxxxxxxxxxxx>@lists.netfilter.org on 06/29/2004 10:17:16 AM Sent by: netfilter-admin@xxxxxxxxxxxxxxxxxxx To: <netfilter@xxxxxxxxxxxxxxxxxxx> cc: Subject: injecting new packets into the netfilter Hi all, I want to know how can we inject absolutely new packets at various hook points in netfilter. I have already seen some questions posted on this earlier too but no replies as such. I am very eager to know about this because using this we can construct some really cool stuff. Currently we are undergoing a project on this and it would be of greate help if somebody can find a solution to this. Thanks in advance for any help on this. regds Mayank
