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Ido Schimmel d3d254e63e drop_monitor: Require 'CAP_SYS_ADMIN' when joining "events" group 
[ Upstream commit e03781879a ]

The "NET_DM" generic netlink family notifies drop locations over the
"events" multicast group. This is problematic since by default generic
netlink allows non-root users to listen to these notifications.

Fix by adding a new field to the generic netlink multicast group
structure that when set prevents non-root users or root without the
'CAP_SYS_ADMIN' capability (in the user namespace owning the network
namespace) from joining the group. Set this field for the "events"
group. Use 'CAP_SYS_ADMIN' rather than 'CAP_NET_ADMIN' because of the
nature of the information that is shared over this group.

Note that the capability check in this case will always be performed
against the initial user namespace since the family is not netns aware
and only operates in the initial network namespace.

A new field is added to the structure rather than using the "flags"
field because the existing field uses uAPI flags and it is inappropriate
to add a new uAPI flag for an internal kernel check. In net-next we can
rework the "flags" field to use internal flags and fold the new field
into it. But for now, in order to reduce the amount of changes, add a
new field.

Since the information can only be consumed by root, mark the control
plane operations that start and stop the tracing as root-only using the
'GENL_ADMIN_PERM' flag.

Tested using [1].

Before:

 # capsh -- -c ./dm_repo
 # capsh --drop=cap_sys_admin -- -c ./dm_repo

After:

 # capsh -- -c ./dm_repo
 # capsh --drop=cap_sys_admin -- -c ./dm_repo
 Failed to join "events" multicast group

[1]
 $ cat dm.c
 #include <stdio.h>
 #include <netlink/genl/ctrl.h>
 #include <netlink/genl/genl.h>
 #include <netlink/socket.h>

 int main(int argc, char **argv)
 {
 	struct nl_sock *sk;
 	int grp, err;

 	sk = nl_socket_alloc();
 	if (!sk) {
 		fprintf(stderr, "Failed to allocate socket\n");
 		return -1;
 	}

 	err = genl_connect(sk);
 	if (err) {
 		fprintf(stderr, "Failed to connect socket\n");
 		return err;
 	}

 	grp = genl_ctrl_resolve_grp(sk, "NET_DM", "events");
 	if (grp < 0) {
 		fprintf(stderr,
 			"Failed to resolve \"events\" multicast group\n");
 		return grp;
 	}

 	err = nl_socket_add_memberships(sk, grp, NFNLGRP_NONE);
 	if (err) {
 		fprintf(stderr, "Failed to join \"events\" multicast group\n");
 		return err;
 	}

 	return 0;
 }
 $ gcc -I/usr/include/libnl3 -lnl-3 -lnl-genl-3 -o dm_repo dm.c

Fixes: 9a8afc8d39 ("Network Drop Monitor: Adding drop monitor implementation & Netlink protocol")
Reported-by: "The UK's National Cyber Security Centre (NCSC)" <security@ncsc.gov.uk>
Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Reviewed-by: Jacob Keller <jacob.e.keller@intel.com>
Reviewed-by: Jiri Pirko <jiri@nvidia.com>
Link: https://lore.kernel.org/r/20231206213102.1824398-3-idosch@nvidia.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
2023-12-13 18:36:38 +01:00
arch parisc: Drop the HP-UX ENOSYM and EREMOTERELEASE error codes 2023-12-08 08:48:02 +01:00
block blk-core: use pr_warn_ratelimited() in bio_check_ro() 2023-11-20 11:08:29 +01:00
certs certs/blacklist_hashes.c: fix const confusion in certs blacklist 2022-06-22 14:22:01 +02:00
crypto crypto: pcrypt - Fix hungtask for PADATA_RESET 2023-11-28 16:56:18 +00:00
Documentation Documentation: sysctl: align cells in second content column 2023-10-25 11:58:54 +02:00
drivers octeontx2-af: Update Tx link register range 2023-12-13 18:36:36 +01:00
fs iomap: update ki_pos a little later in iomap_dio_complete 2023-12-08 08:48:05 +01:00
include drop_monitor: Require 'CAP_SYS_ADMIN' when joining "events" group 2023-12-13 18:36:38 +01:00
init proc: sysctl: prevent aliased sysctls from getting passed to init 2023-12-03 07:31:24 +01:00
io_uring io_uring: fix off-by one bvec index 2023-12-03 07:31:26 +01:00
ipc ipc/sem: Fix dangling sem_array access in semtimedop race 2022-12-08 11:28:45 +01:00
kernel hrtimers: Push pending hrtimers away from outgoing CPU earlier 2023-12-13 18:36:31 +01:00
lib parisc: Drop the HP-UX ENOSYM and EREMOTERELEASE error codes 2023-12-08 08:48:02 +01:00
LICENSES LICENSES/dual/CC-BY-4.0: Git rid of "smart quotes" 2021-07-15 06:31:24 -06:00
mm mm: kmem: drop __GFP_NOFAIL when allocating objcg vectors 2023-11-28 16:56:35 +00:00
net drop_monitor: Require 'CAP_SYS_ADMIN' when joining "events" group 2023-12-13 18:36:38 +01:00
samples samples/hw_breakpoint: fix building without module unloading 2023-09-23 11:10:01 +02:00
scripts kconfig: fix memory leak from range properties 2023-12-13 18:36:32 +01:00
security KEYS: trusted: Rollback init_trusted() consistently 2023-11-28 16:56:30 +00:00
sound ASoC: SOF: sof-pci-dev: Fix community key quirk detection 2023-12-08 08:48:04 +01:00
tools selftests/resctrl: Move _GNU_SOURCE define into Makefile 2023-12-08 08:48:04 +01:00
usr usr/include/Makefile: add linux/nfc.h to the compile-test coverage 2022-02-01 17:27:15 +01:00
virt KVM: Grab a reference to KVM for VM and vCPU stats file descriptors 2023-08-03 10:22:40 +02:00
.clang-format clang-format: Update with the latest for_each macro list 2021-05-12 23:32:39 +02:00
.cocciconfig
.get_maintainer.ignore Opt out of scripts/get_maintainer.pl 2019-05-16 10:53:40 -07:00
.gitattributes .gitattributes: use 'dts' diff driver for dts files 2019-12-04 19:44:11 -08:00
.gitignore .gitignore: ignore only top-level modules.builtin 2021-05-02 00:43:35 +09:00
.mailmap mailmap: add Andrej Shadura 2021-10-18 20:22:03 -10:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS MAINTAINERS: Move Daniel Drake to credits 2021-09-21 08:34:58 +03:00
Kbuild kbuild: rename hostprogs-y/always to hostprogs/always-y 2020-02-04 01:53:07 +09:00
Kconfig kbuild: ensure full rebuild when the compiler is updated 2020-05-12 13:28:33 +09:00
MAINTAINERS iio: stx104: Move to addac subdirectory 2023-08-26 14:23:27 +02:00
Makefile Linux 5.15.142 2023-12-08 08:48:05 +01:00
README Drop all 00-INDEX files from Documentation/ 2018-09-09 15:08:58 -06:00

README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.