From 017598b41e59aa0bdb121020c29746cd062cdec0 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Yaroslav=20de=20la=20Pe=C3=B1a=20Smirnov?= Date: Sat, 11 Feb 2023 01:51:36 +0300 Subject: init --- .gitignore | 10 ++ README.md | 30 ++++++ ks/.exrc | 4 + ks/COPYING | 7 ++ ks/LICENSE | 339 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ ks/Makefile | 11 ++ ks/genltest.c | 215 +++++++++++++++++++++++++++++++++++++ ks/genltest.h | 31 ++++++ us/.exrc | 3 + us/COPYING | 7 ++ us/LICENSE | 339 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ us/Makefile | 2 + us/genltest.c | 178 ++++++++++++++++++++++++++++++ 13 files changed, 1176 insertions(+) create mode 100644 .gitignore create mode 100644 README.md create mode 100644 ks/.exrc create mode 100644 ks/COPYING create mode 100644 ks/LICENSE create mode 100644 ks/Makefile create mode 100644 ks/genltest.c create mode 100644 ks/genltest.h create mode 100644 us/.exrc create mode 100644 us/COPYING create mode 100644 us/LICENSE create mode 100644 us/Makefile create mode 100644 us/genltest.c diff --git a/.gitignore b/.gitignore new file mode 100644 index 0000000..a28ffa6 --- /dev/null +++ b/.gitignore @@ -0,0 +1,10 @@ +.cache/ +compile_commands.json +*.ko +*.cmd +*.o +*.mod +*.mod.* +*.symvers +*.order +us/genltest diff --git a/README.md b/README.md new file mode 100644 index 0000000..6b02651 --- /dev/null +++ b/README.md @@ -0,0 +1,30 @@ +# Generic Netlink example + +This repository contains an example of how to use the Generic Netlink +communication protocol of the Linux Kernel both in kernel space and user space. + +For more information read my introductory article +[here](https://www.yaroslavps.com/weblog/genl-intro/); or if you are the +adventurous kind just read the source, it's got plenty of comments :) + +## Build and run + +### Kernel module + +In order to build the kernel module you need to have installed the Linux kernel +headers in your system. + +Once you've got the requirements covered just switch to the `ks/` directory and +`make` it. + +If the build completed successfully, you should be able to load the +`genltest.ko` module using insmod. + +### User space program + +In order to build the program you need to have libnl installed. + +Once installed just switch to the `us/` directory and `make` it. + +If the build completed successfully, and once you have loaded the aforementioned +`genltest.ko` module, you should be able to run the program `./genltest`. diff --git a/ks/.exrc b/ks/.exrc new file mode 100644 index 0000000..cc55546 --- /dev/null +++ b/ks/.exrc @@ -0,0 +1,4 @@ +let ch_syntax_for_h = 1 +set ts=8 +set sw=8 +lua vim.diagnostic.disable() diff --git a/ks/COPYING b/ks/COPYING new file mode 100644 index 0000000..3d4fad0 --- /dev/null +++ b/ks/COPYING @@ -0,0 +1,7 @@ +Copyright (c) 2022 Yaroslav de la Peña Smirnov + +This is free software, which you can redistribute and/or modify under the terms +of the GNU General Public License, version 2.0 only, unless otherwise noted +inside of individual source files. It is provided AS IS and WITHOUT ANY WARRANTY +whatsoever. For more information read the LICENSE file and/or the individual +source file. diff --git a/ks/LICENSE b/ks/LICENSE new file mode 100644 index 0000000..d159169 --- /dev/null +++ b/ks/LICENSE @@ -0,0 +1,339 @@ + GNU GENERAL PUBLIC LICENSE + Version 2, June 1991 + + Copyright (C) 1989, 1991 Free Software Foundation, Inc., + 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA + Everyone is permitted to copy and distribute verbatim copies + of this license document, but changing it is not allowed. + + Preamble + + The licenses for most software are designed to take away your +freedom to share and change it. By contrast, the GNU General Public +License is intended to guarantee your freedom to share and change free +software--to make sure the software is free for all its users. This +General Public License applies to most of the Free Software +Foundation's software and to any other program whose authors commit to +using it. (Some other Free Software Foundation software is covered by +the GNU Lesser General Public License instead.) You can apply it to +your programs, too. + + When we speak of free software, we are referring to freedom, not +price. Our General Public Licenses are designed to make sure that you +have the freedom to distribute copies of free software (and charge for +this service if you wish), that you receive source code or can get it +if you want it, that you can change the software or use pieces of it +in new free programs; and that you know you can do these things. + + To protect your rights, we need to make restrictions that forbid +anyone to deny you these rights or to ask you to surrender the rights. +These restrictions translate to certain responsibilities for you if you +distribute copies of the software, or if you modify it. + + For example, if you distribute copies of such a program, whether +gratis or for a fee, you must give the recipients all the rights that +you have. 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See the + GNU General Public License for more details. + + You should have received a copy of the GNU General Public License along + with this program; if not, write to the Free Software Foundation, Inc., + 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA. + +Also add information on how to contact you by electronic and paper mail. + +If the program is interactive, make it output a short notice like this +when it starts in an interactive mode: + + Gnomovision version 69, Copyright (C) year name of author + Gnomovision comes with ABSOLUTELY NO WARRANTY; for details type `show w'. + This is free software, and you are welcome to redistribute it + under certain conditions; type `show c' for details. + +The hypothetical commands `show w' and `show c' should show the appropriate +parts of the General Public License. Of course, the commands you use may +be called something other than `show w' and `show c'; they could even be +mouse-clicks or menu items--whatever suits your program. + +You should also get your employer (if you work as a programmer) or your +school, if any, to sign a "copyright disclaimer" for the program, if +necessary. Here is a sample; alter the names: + + Yoyodyne, Inc., hereby disclaims all copyright interest in the program + `Gnomovision' (which makes passes at compilers) written by James Hacker. + + , 1 April 1989 + Ty Coon, President of Vice + +This General Public License does not permit incorporating your program into +proprietary programs. If your program is a subroutine library, you may +consider it more useful to permit linking proprietary applications with the +library. If this is what you want to do, use the GNU Lesser General +Public License instead of this License. diff --git a/ks/Makefile b/ks/Makefile new file mode 100644 index 0000000..54301de --- /dev/null +++ b/ks/Makefile @@ -0,0 +1,11 @@ +KERNELDIR := /lib/modules/$(shell uname -r)/build +# CFLAGS_genltest.o := -O0 +obj-m += genltest.o + +all: + $(MAKE) -C $(KERNELDIR) V=0 M=`pwd` modules +clean: + #$(MAKE) -C $(KERNELDIR) M=`pwd` clean + @rm -f *.ko *.o modules.order Module.symvers *.mod.? *~ + @rm -rf .tmp_versions .cache.mk *.ur-safe *.mod + diff --git a/ks/genltest.c b/ks/genltest.c new file mode 100644 index 0000000..fa9a960 --- /dev/null +++ b/ks/genltest.c @@ -0,0 +1,215 @@ +/* SPDX-License-Identifier: GPL-2.0 */ +/* + * Generic Netlink example module + * + * An example on how to use the Generic Netlink API with ops and multicast + * groups. + * + * Copyright (c) 2022 Yaroslav de la Peña Smirnov + */ +#define pr_fmt(fmt) "genltest: " fmt + +#include "genltest.h" + +#include +#include + +/* + * Some materials that were used as source for this example/tutorial/guide: + * + * - https://wiki.linuxfoundation.org/networking/generic_netlink_howto + * - https://kernel.org/doc/html/next/userspace-api/netlink/intro.html + */ + +#define MSG_MAX_LEN 1024 + +/* Forward declaration */ +static struct genl_family genl_fam; + +/* Handler for GENLTEST_CMD_ECHO messages received */ +static int echo_doit(struct sk_buff *skb, struct genl_info *info) +{ + int ret = 0; + void *hdr; + struct sk_buff *msg; + + /* Check if the attribute is present and print it */ + if (info->attrs[GENLTEST_A_MSG]) { + char *str = nla_data(info->attrs[GENLTEST_A_MSG]); + pr_info("message received: %s\n", str); + } else { + pr_info("empty message received\n"); + } + + /* Allocate a new buffer for the reply */ + msg = nlmsg_new(NLMSG_DEFAULT_SIZE, GFP_KERNEL); + if (!msg) { + pr_err("failed to allocate message buffer\n"); + return -ENOMEM; + } + + /* Put the Generic Netlink header */ + hdr = genlmsg_put(msg, info->snd_portid, info->snd_seq, &genl_fam, 0, + GENLTEST_CMD_ECHO); + if (!hdr) { + pr_err("failed to create genetlink header\n"); + nlmsg_free(msg); + return -EMSGSIZE; + } + /* And the message */ + if ((ret = nla_put_string(msg, GENLTEST_A_MSG, + "Hello from Kernel Space, Netlink!"))) { + pr_err("failed to create message string\n"); + genlmsg_cancel(msg, hdr); + nlmsg_free(msg); + goto out; + } + + /* Finalize the message and send it */ + genlmsg_end(msg, hdr); + + ret = genlmsg_reply(msg, info); + pr_info("reply sent\n"); + +out: + return ret; +} + +/* Attribute validation policy for our echo command */ +static struct nla_policy echo_pol[GENLTEST_A_MAX + 1] = { + [GENLTEST_A_MSG] = { .type = NLA_NUL_STRING }, +}; + +/* Operations for our Generic Netlink family */ +static struct genl_ops genl_ops[] = { + { + .cmd = GENLTEST_CMD_ECHO, + .policy = echo_pol, + .doit = echo_doit, + }, +}; + +/* Multicast groups for our family */ +static const struct genl_multicast_group genl_mcgrps[] = { + { .name = GENLTEST_MC_GRP_NAME }, +}; + +/* Generic Netlink family */ +static struct genl_family genl_fam = { + .name = GENLTEST_GENL_NAME, + .version = GENLTEST_GENL_VERSION, + .maxattr = GENLTEST_A_MAX, + .ops = genl_ops, + .n_ops = ARRAY_SIZE(genl_ops), + .mcgrps = genl_mcgrps, + .n_mcgrps = ARRAY_SIZE(genl_mcgrps), +}; + +/* Multicast ping message to our genl multicast group */ +static int echo_ping(const char *buf, size_t cnt) +{ + int ret = 0; + void *hdr; + /* Allocate message buffer */ + struct sk_buff *skb = genlmsg_new(NLMSG_DEFAULT_SIZE, GFP_KERNEL); + + if (unlikely(!skb)) { + pr_err("failed to allocate memory for genl message\n"); + return -ENOMEM; + } + + /* Put the Generic Netlink header */ + hdr = genlmsg_put(skb, 0, 0, &genl_fam, 0, GENLTEST_CMD_ECHO); + if (unlikely(!hdr)) { + pr_err("failed to allocate memory for genl header\n"); + nlmsg_free(skb); + return -ENOMEM; + } + + /* And the message */ + if ((ret = nla_put_string(skb, GENLTEST_A_MSG, buf))) { + pr_err("unable to create message string\n"); + genlmsg_cancel(skb, hdr); + nlmsg_free(skb); + return ret; + } + + /* Finalize the message */ + genlmsg_end(skb, hdr); + + /* Send it over multicast to the 0-th mc group in our array. */ + ret = genlmsg_multicast(&genl_fam, skb, 0, 0, GFP_KERNEL); + if (ret == -ESRCH) { + pr_warn("multicast message sent, but nobody was listening...\n"); + } else if (ret) { + pr_err("failed to send multicast genl message\n"); + } else { + pr_info("multicast message sent\n"); + } + + return ret; +} + +/* + * Test sysfs attr to send multicast messages. The string in the buffer will be + * echoed to the multicast group. + */ +static ssize_t ping_store(struct kobject *kobj, struct kobj_attribute *attr, + const char *buf, size_t cnt) +{ + int max = cnt > MSG_MAX_LEN ? MSG_MAX_LEN : cnt; + echo_ping(buf, max); + + return max; +} + +static struct kobject *kobj; +static struct kobj_attribute ping_attr = __ATTR_WO(ping); + +static int __init init_genltest(void) +{ + int ret = 0; + + pr_info("init start\n"); + + kobj = kobject_create_and_add("genltest", kobj); + if (unlikely(!kobj)) { + pr_err("unable to create kobject\n"); + return -ENOMEM; + } + ret = sysfs_create_file(kobj, &ping_attr.attr); + if (unlikely(ret)) { + pr_err("unable to create sysfs file\n"); + kobject_put(kobj); + return ret; + } + + ret = genl_register_family(&genl_fam); + if (unlikely(ret)) { + pr_crit("failed to register generic netlink family\n"); + sysfs_remove_file(kobj, &ping_attr.attr); + kobject_put(kobj); + } + + pr_info("init end\n"); + + return ret; +} + +static void __exit exit_genltest(void) +{ + if (unlikely(genl_unregister_family(&genl_fam))) { + pr_err("failed to unregister generic netlink family\n"); + } + + sysfs_remove_file(kobj, &ping_attr.attr); + kobject_put(kobj); + + pr_info("exit\n"); +} + +MODULE_AUTHOR("Yaroslav de la Peña Smirnov"); +MODULE_LICENSE("GPL"); + +module_init(init_genltest); +module_exit(exit_genltest); diff --git a/ks/genltest.h b/ks/genltest.h new file mode 100644 index 0000000..bd947a3 --- /dev/null +++ b/ks/genltest.h @@ -0,0 +1,31 @@ +#ifndef GENLTEST_H +#define GENLTEST_H + +/* + * This header includes definitions that are shared with kernel space and user + * space. This header would be put in a place visible to user space. + */ + +#define GENLTEST_GENL_NAME "genltest" +#define GENLTEST_GENL_VERSION 1 +#define GENLTEST_MC_GRP_NAME "mcgrp" + +/* Attributes */ +enum genltest_attrs { + GENLTEST_A_UNSPEC, + GENLTEST_A_MSG, + __GENLTEST_A_MAX, +}; + +#define GENLTEST_A_MAX (__GENLTEST_A_MAX - 1) + +/* Commands */ +enum genltest_cmds { + GENLTEST_CMD_UNSPEC, + GENLTEST_CMD_ECHO, + __GENLTEST_CMD_MAX, +}; + +#define GENLTEST_CMD_MAX (__GENLTEST_CMD_MAX - 1) + +#endif diff --git a/us/.exrc b/us/.exrc new file mode 100644 index 0000000..8d44102 --- /dev/null +++ b/us/.exrc @@ -0,0 +1,3 @@ +let ch_syntax_for_h = 1 +set ts=8 +set sw=8 diff --git a/us/COPYING b/us/COPYING new file mode 100644 index 0000000..3d4fad0 --- /dev/null +++ b/us/COPYING @@ -0,0 +1,7 @@ +Copyright (c) 2022 Yaroslav de la Peña Smirnov + +This is free software, which you can redistribute and/or modify under the terms +of the GNU General Public License, version 2.0 only, unless otherwise noted +inside of individual source files. It is provided AS IS and WITHOUT ANY WARRANTY +whatsoever. For more information read the LICENSE file and/or the individual +source file. diff --git a/us/LICENSE b/us/LICENSE new file mode 100644 index 0000000..d159169 --- /dev/null +++ b/us/LICENSE @@ -0,0 +1,339 @@ + GNU GENERAL PUBLIC LICENSE + Version 2, June 1991 + + Copyright (C) 1989, 1991 Free Software Foundation, Inc., + 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA + Everyone is permitted to copy and distribute verbatim copies + of this license document, but changing it is not allowed. + + Preamble + + The licenses for most software are designed to take away your +freedom to share and change it. By contrast, the GNU General Public +License is intended to guarantee your freedom to share and change free +software--to make sure the software is free for all its users. This +General Public License applies to most of the Free Software +Foundation's software and to any other program whose authors commit to +using it. (Some other Free Software Foundation software is covered by +the GNU Lesser General Public License instead.) You can apply it to +your programs, too. + + When we speak of free software, we are referring to freedom, not +price. Our General Public Licenses are designed to make sure that you +have the freedom to distribute copies of free software (and charge for +this service if you wish), that you receive source code or can get it +if you want it, that you can change the software or use pieces of it +in new free programs; and that you know you can do these things. + + To protect your rights, we need to make restrictions that forbid +anyone to deny you these rights or to ask you to surrender the rights. +These restrictions translate to certain responsibilities for you if you +distribute copies of the software, or if you modify it. + + For example, if you distribute copies of such a program, whether +gratis or for a fee, you must give the recipients all the rights that +you have. 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You may copy and distribute verbatim copies of the Program's +source code as you receive it, in any medium, provided that you +conspicuously and appropriately publish on each copy an appropriate +copyright notice and disclaimer of warranty; keep intact all the +notices that refer to this License and to the absence of any warranty; +and give any other recipients of the Program a copy of this License +along with the Program. + +You may charge a fee for the physical act of transferring a copy, and +you may at your option offer warranty protection in exchange for a fee. + + 2. You may modify your copy or copies of the Program or any portion +of it, thus forming a work based on the Program, and copy and +distribute such modifications or work under the terms of Section 1 +above, provided that you also meet all of these conditions: + + a) You must cause the modified files to carry prominent notices + stating that you changed the files and the date of any change. + + b) You must cause any work that you distribute or publish, that in + whole or in part contains or is derived from the Program or any + part thereof, to be licensed as a whole at no charge to all third + parties under the terms of this License. + + c) If the modified program normally reads commands interactively + when run, you must cause it, when started running for such + interactive use in the most ordinary way, to print or display an + announcement including an appropriate copyright notice and a + notice that there is no warranty (or else, saying that you provide + a warranty) and that users may redistribute the program under + these conditions, and telling the user how to view a copy of this + License. (Exception: if the Program itself is interactive but + does not normally print such an announcement, your work based on + the Program is not required to print an announcement.) + +These requirements apply to the modified work as a whole. If +identifiable sections of that work are not derived from the Program, +and can be reasonably considered independent and separate works in +themselves, then this License, and its terms, do not apply to those +sections when you distribute them as separate works. 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You may copy and distribute the Program (or a work based on it, +under Section 2) in object code or executable form under the terms of +Sections 1 and 2 above provided that you also do one of the following: + + a) Accompany it with the complete corresponding machine-readable + source code, which must be distributed under the terms of Sections + 1 and 2 above on a medium customarily used for software interchange; or, + + b) Accompany it with a written offer, valid for at least three + years, to give any third party, for a charge no more than your + cost of physically performing source distribution, a complete + machine-readable copy of the corresponding source code, to be + distributed under the terms of Sections 1 and 2 above on a medium + customarily used for software interchange; or, + + c) Accompany it with the information you received as to the offer + to distribute corresponding source code. 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Each time you redistribute the Program (or any work based on the +Program), the recipient automatically receives a license from the +original licensor to copy, distribute or modify the Program subject to +these terms and conditions. You may not impose any further +restrictions on the recipients' exercise of the rights granted herein. +You are not responsible for enforcing compliance by third parties to +this License. + + 7. If, as a consequence of a court judgment or allegation of patent +infringement or for any other reason (not limited to patent issues), +conditions are imposed on you (whether by court order, agreement or +otherwise) that contradict the conditions of this License, they do not +excuse you from the conditions of this License. If you cannot +distribute so as to satisfy simultaneously your obligations under this +License and any other pertinent obligations, then as a consequence you +may not distribute the Program at all. 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The Free Software Foundation may publish revised and/or new versions +of the General Public License from time to time. Such new versions will +be similar in spirit to the present version, but may differ in detail to +address new problems or concerns. + +Each version is given a distinguishing version number. If the Program +specifies a version number of this License which applies to it and "any +later version", you have the option of following the terms and conditions +either of that version or of any later version published by the Free +Software Foundation. If the Program does not specify a version number of +this License, you may choose any version ever published by the Free Software +Foundation. + + 10. If you wish to incorporate parts of the Program into other free +programs whose distribution conditions are different, write to the author +to ask for permission. For software which is copyrighted by the Free +Software Foundation, write to the Free Software Foundation; we sometimes +make exceptions for this. Our decision will be guided by the two goals +of preserving the free status of all derivatives of our free software and +of promoting the sharing and reuse of software generally. + + NO WARRANTY + + 11. BECAUSE THE PROGRAM IS LICENSED FREE OF CHARGE, THERE IS NO WARRANTY +FOR THE PROGRAM, TO THE EXTENT PERMITTED BY APPLICABLE LAW. EXCEPT WHEN +OTHERWISE STATED IN WRITING THE COPYRIGHT HOLDERS AND/OR OTHER PARTIES +PROVIDE THE PROGRAM "AS IS" WITHOUT WARRANTY OF ANY KIND, EITHER EXPRESSED +OR IMPLIED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF +MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. THE ENTIRE RISK AS +TO THE QUALITY AND PERFORMANCE OF THE PROGRAM IS WITH YOU. SHOULD THE +PROGRAM PROVE DEFECTIVE, YOU ASSUME THE COST OF ALL NECESSARY SERVICING, +REPAIR OR CORRECTION. + + 12. IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING +WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MAY MODIFY AND/OR +REDISTRIBUTE THE PROGRAM AS PERMITTED ABOVE, BE LIABLE TO YOU FOR DAMAGES, +INCLUDING ANY GENERAL, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING +OUT OF THE USE OR INABILITY TO USE THE PROGRAM (INCLUDING BUT NOT LIMITED +TO LOSS OF DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY +YOU OR THIRD PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE WITH ANY OTHER +PROGRAMS), EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE +POSSIBILITY OF SUCH DAMAGES. + + END OF TERMS AND CONDITIONS + + How to Apply These Terms to Your New Programs + + If you develop a new program, and you want it to be of the greatest +possible use to the public, the best way to achieve this is to make it +free software which everyone can redistribute and change under these terms. + + To do so, attach the following notices to the program. It is safest +to attach them to the start of each source file to most effectively +convey the exclusion of warranty; and each file should have at least +the "copyright" line and a pointer to where the full notice is found. + + + Copyright (C) + + This program is free software; you can redistribute it and/or modify + it under the terms of the GNU General Public License as published by + the Free Software Foundation; either version 2 of the License, or + (at your option) any later version. + + This program is distributed in the hope that it will be useful, + but WITHOUT ANY WARRANTY; without even the implied warranty of + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the + GNU General Public License for more details. + + You should have received a copy of the GNU General Public License along + with this program; if not, write to the Free Software Foundation, Inc., + 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA. + +Also add information on how to contact you by electronic and paper mail. + +If the program is interactive, make it output a short notice like this +when it starts in an interactive mode: + + Gnomovision version 69, Copyright (C) year name of author + Gnomovision comes with ABSOLUTELY NO WARRANTY; for details type `show w'. + This is free software, and you are welcome to redistribute it + under certain conditions; type `show c' for details. + +The hypothetical commands `show w' and `show c' should show the appropriate +parts of the General Public License. Of course, the commands you use may +be called something other than `show w' and `show c'; they could even be +mouse-clicks or menu items--whatever suits your program. + +You should also get your employer (if you work as a programmer) or your +school, if any, to sign a "copyright disclaimer" for the program, if +necessary. Here is a sample; alter the names: + + Yoyodyne, Inc., hereby disclaims all copyright interest in the program + `Gnomovision' (which makes passes at compilers) written by James Hacker. + + , 1 April 1989 + Ty Coon, President of Vice + +This General Public License does not permit incorporating your program into +proprietary programs. If your program is a subroutine library, you may +consider it more useful to permit linking proprietary applications with the +library. If this is what you want to do, use the GNU Lesser General +Public License instead of this License. diff --git a/us/Makefile b/us/Makefile new file mode 100644 index 0000000..41b84ea --- /dev/null +++ b/us/Makefile @@ -0,0 +1,2 @@ +all: genltest.c + gcc genltest.c $(shell pkg-config --cflags --libs libnl-3.0 libnl-genl-3.0) -o genltest diff --git a/us/genltest.c b/us/genltest.c new file mode 100644 index 0000000..caf44f5 --- /dev/null +++ b/us/genltest.c @@ -0,0 +1,178 @@ +/* SPDX-License-Identifier: GPL-2.0 */ +/* + * Generic Netlink libnl example program + * + * An example on how to use the libnl library for communicating over Generic + * Netlink with kernel modules, with unicast and multicast group messages. + * + * Copyright (c) 2022 Yaroslav de la Peña Smirnov + */ +#include +#include +#include +#include +#include +#include +#include +#include +#include + +#include "../ks/genltest.h" + +#define prerr(...) fprintf(stderr, "error: " __VA_ARGS__) + +/* + * libnl docs and API: https://www.infradead.org/~tgr/libnl/ + * Current libnl repo: https://github.com/thom311/libnl + */ + +/* + * Handler for all received messages from our Generic Netlink family, both + * unicast and multicast. + */ +static int echo_reply_handler(struct nl_msg *msg, void *arg) +{ + int err = 0; + struct genlmsghdr *genlhdr = nlmsg_data(nlmsg_hdr(msg)); + struct nlattr *tb[GENLTEST_A_MAX + 1]; + + /* Parse the attributes */ + err = nla_parse(tb, GENLTEST_A_MAX, genlmsg_attrdata(genlhdr, 0), + genlmsg_attrlen(genlhdr, 0), NULL); + if (err) { + prerr("unable to parse message: %s\n", strerror(-err)); + return NL_SKIP; + } + /* Check that there's actually a payload */ + if (!tb[GENLTEST_A_MSG]) { + prerr("msg attribute missing from message\n"); + return NL_SKIP; + } + + /* Print it! */ + printf("message received: %s\n", nla_get_string(tb[GENLTEST_A_MSG])); + + return NL_OK; +} + +/* Send (unicast) GENLTEST_CMD_ECHO request message */ +static int send_echo_msg(struct nl_sock *sk, int fam) +{ + int err = 0; + struct nl_msg *msg = nlmsg_alloc(); + if (!msg) { + return -ENOMEM; + } + + /* Put the genl header inside message buffer */ + void *hdr = genlmsg_put(msg, NL_AUTO_PORT, NL_AUTO_SEQ, fam, 0, 0, + GENLTEST_CMD_ECHO, GENLTEST_GENL_VERSION); + if (!hdr) { + return -EMSGSIZE; + } + + /* Put the string inside the message. */ + err = nla_put_string(msg, GENLTEST_A_MSG, + "Hello from User Space, Netlink!"); + if (err < 0) { + return -err; + } + printf("message sent\n"); + + /* Send the message. */ + err = nl_send_auto(sk, msg); + err = err >= 0 ? 0 : err; + + nlmsg_free(msg); + + return err; +} + +/* Allocate netlink socket and connect to generic netlink */ +static int conn(struct nl_sock **sk) +{ + *sk = nl_socket_alloc(); + if (!sk) { + return -ENOMEM; + } + + return genl_connect(*sk); +} + +/* Disconnect and release socket */ +static void disconn(struct nl_sock *sk) +{ + nl_close(sk); + nl_socket_free(sk); +} + +/* Modify the callback for replies to handle all received messages */ +static inline int set_cb(struct nl_sock *sk) +{ + return nl_socket_modify_cb(sk, NL_CB_VALID, NL_CB_CUSTOM, + echo_reply_handler, NULL); +} + +int main(void) +{ + int ret = 1; + struct nl_sock *ucsk, *mcsk; + + /* + * We use one socket to receive asynchronous "notifications" over + * multicast group, and another for ops. We do this so that we don't mix + * up responses from ops with notifications to make handling easier. + */ + if ((ret = conn(&ucsk)) || (ret = conn(&mcsk))) { + prerr("failed to connect to generic netlink\n"); + goto out; + } + + /* Resolve the genl family. One family for both unicast and multicast. */ + int fam = genl_ctrl_resolve(ucsk, GENLTEST_GENL_NAME); + if (fam < 0) { + prerr("failed to resolve generic netlink family: %s\n", + strerror(-fam)); + goto out; + } + + /* Disable sequence checks for asynchronous multicast messages. */ + nl_socket_disable_seq_check(mcsk); + + /* Resolve the multicast group. */ + int mcgrp = genl_ctrl_resolve_grp(mcsk, GENLTEST_GENL_NAME, + GENLTEST_MC_GRP_NAME); + if (mcgrp < 0) { + prerr("failed to resolve generic netlink multicast group: %s\n", + strerror(-mcgrp)); + goto out; + } + /* Join the multicast group. */ + if ((ret = nl_socket_add_membership(mcsk, mcgrp) < 0)) { + prerr("failed to join multicast group: %s\n", strerror(-ret)); + goto out; + } + + if ((ret = set_cb(ucsk)) || (ret = set_cb(mcsk))) { + prerr("failed to set callback: %s\n", strerror(-ret)); + goto out; + } + + /* Send unicast message and listen for response. */ + if ((ret = send_echo_msg(ucsk, fam))) { + prerr("failed to send message: %s\n", strerror(-ret)); + } + printf("listening for messages\n"); + nl_recvmsgs_default(ucsk); + + /* Listen for "notifications". */ + while (1) { + nl_recvmsgs_default(mcsk); + } + + ret = 0; +out: + disconn(ucsk); + disconn(mcsk); + return ret; +} -- cgit v1.2.3