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Message-ID: <ZXGfMncXs/sqF7XJ@nanopsycho>
Date: Thu, 7 Dec 2023 11:32:18 +0100
From: Jiri Pirko <jiri@...nulli.us>
To: Jamal Hadi Salim <jhs@...atatu.com>
Cc: Ido Schimmel <idosch@...dia.com>, netdev@...r.kernel.org,
davem@...emloft.net, kuba@...nel.org, pabeni@...hat.com,
edumazet@...gle.com, nhorman@...driver.com, yotam.gi@...il.com,
johannes@...solutions.net, jacob.e.keller@...el.com,
horms@...nel.org, andriy.shevchenko@...ux.intel.com
Subject: Re: [PATCH net 1/2] psample: Require 'CAP_NET_ADMIN' when joining
"packets" group
Thu, Dec 07, 2023 at 11:16:30AM CET, jhs@...atatu.com wrote:
>On Wed, Dec 6, 2023 at 4:33 PM Ido Schimmel <idosch@...dia.com> wrote:
>>
>> The "psample" generic netlink family notifies sampled packets over the
>> "packets" multicast group. This is problematic since by default generic
>> netlink allows non-root users to listen to these notifications.
>>
>> Fix by marking the group with the 'GENL_UNS_ADMIN_PERM' flag. This will
>> prevent non-root users or root without the 'CAP_NET_ADMIN' capability
>> (in the user namespace owning the network namespace) from joining the
>> group.
>>
>
>Out of curiosity, shouldnt reading/getting also be disallowed then?
This is about the sampled packets. You only get them by notifications.
>Traditionally both listening and reading has been allowed without root
>for most netlink endpoints...
>IOW, if i cant listen but am able to dump, isnt whatever "security
>hole" still in play even after this change?
>
>cheers,
>jamal
>
>
>
>> Tested using [1].
>>
>> Before:
>>
>> # capsh -- -c ./psample_repo
>> # capsh --drop=cap_net_admin -- -c ./psample_repo
>>
>> After:
>>
>> # capsh -- -c ./psample_repo
>> # capsh --drop=cap_net_admin -- -c ./psample_repo
>> Failed to join "packets" multicast group
>>
>> [1]
>> $ cat psample.c
>> #include <stdio.h>
>> #include <netlink/genl/ctrl.h>
>> #include <netlink/genl/genl.h>
>> #include <netlink/socket.h>
>>
>> int join_grp(struct nl_sock *sk, const char *grp_name)
>> {
>> int grp, err;
>>
>> grp = genl_ctrl_resolve_grp(sk, "psample", grp_name);
>> if (grp < 0) {
>> fprintf(stderr, "Failed to resolve \"%s\" multicast group\n",
>> grp_name);
>> return grp;
>> }
>>
>> err = nl_socket_add_memberships(sk, grp, NFNLGRP_NONE);
>> if (err) {
>> fprintf(stderr, "Failed to join \"%s\" multicast group\n",
>> grp_name);
>> return err;
>> }
>>
>> return 0;
>> }
>>
>> int main(int argc, char **argv)
>> {
>> struct nl_sock *sk;
>> int 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;
>> }
>>
>> err = join_grp(sk, "config");
>> if (err)
>> return err;
>>
>> err = join_grp(sk, "packets");
>> if (err)
>> return err;
>>
>> return 0;
>> }
>> $ gcc -I/usr/include/libnl3 -lnl-3 -lnl-genl-3 -o psample_repo psample.c
>>
>> Fixes: 6ae0a6286171 ("net: Introduce psample, a new genetlink channel for packet sampling")
>> Reported-by: "The UK's National Cyber Security Centre (NCSC)" <security@...c.gov.uk>
>> Signed-off-by: Ido Schimmel <idosch@...dia.com>
>> ---
>> net/psample/psample.c | 3 ++-
>> 1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/net/psample/psample.c b/net/psample/psample.c
>> index 81a794e36f53..c34e902855db 100644
>> --- a/net/psample/psample.c
>> +++ b/net/psample/psample.c
>> @@ -31,7 +31,8 @@ enum psample_nl_multicast_groups {
>>
>> static const struct genl_multicast_group psample_nl_mcgrps[] = {
>> [PSAMPLE_NL_MCGRP_CONFIG] = { .name = PSAMPLE_NL_MCGRP_CONFIG_NAME },
>> - [PSAMPLE_NL_MCGRP_SAMPLE] = { .name = PSAMPLE_NL_MCGRP_SAMPLE_NAME },
>> + [PSAMPLE_NL_MCGRP_SAMPLE] = { .name = PSAMPLE_NL_MCGRP_SAMPLE_NAME,
>> + .flags = GENL_UNS_ADMIN_PERM },
>> };
>>
>> static struct genl_family psample_nl_family __ro_after_init;
>> --
>> 2.40.1
>>
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