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linux/net/psample/psample.c
Ido Schimmel 44ec98ea5e psample: Require 'CAP_NET_ADMIN' when joining "packets" group 
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.

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: 6ae0a62861 ("net: Introduce psample, a new genetlink channel for packet sampling")
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/20231206213102.1824398-2-idosch@nvidia.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
2023-12-07 09:54:02 -08:00

514 lines
13 KiB
C
Raw Blame History

// SPDX-License-Identifier: GPL-2.0-only
/*
* net/psample/psample.c - Netlink channel for packet sampling
* Copyright (c) 2017 Yotam Gigi <yotamg@mellanox.com>
*/
#include <linux/types.h>
#include <linux/kernel.h>
#include <linux/skbuff.h>
#include <linux/module.h>
#include <linux/timekeeping.h>
#include <net/net_namespace.h>
#include <net/sock.h>
#include <net/netlink.h>
#include <net/genetlink.h>
#include <net/psample.h>
#include <linux/spinlock.h>
#include <net/ip_tunnels.h>
#include <net/dst_metadata.h>
#define PSAMPLE_MAX_PACKET_SIZE 0xffff
static LIST_HEAD(psample_groups_list);
static DEFINE_SPINLOCK(psample_groups_lock);
/* multicast groups */
enum psample_nl_multicast_groups {
PSAMPLE_NL_MCGRP_CONFIG,
PSAMPLE_NL_MCGRP_SAMPLE,
};
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,
.flags = GENL_UNS_ADMIN_PERM },
};
static struct genl_family psample_nl_family __ro_after_init;
static int psample_group_nl_fill(struct sk_buff *msg,
struct psample_group *group,
enum psample_command cmd, u32 portid, u32 seq,
int flags)
{
void *hdr;
int ret;
hdr = genlmsg_put(msg, portid, seq, &psample_nl_family, flags, cmd);
if (!hdr)
return -EMSGSIZE;
ret = nla_put_u32(msg, PSAMPLE_ATTR_SAMPLE_GROUP, group->group_num);
if (ret < 0)
goto error;
ret = nla_put_u32(msg, PSAMPLE_ATTR_GROUP_REFCOUNT, group->refcount);
if (ret < 0)
goto error;
ret = nla_put_u32(msg, PSAMPLE_ATTR_GROUP_SEQ, group->seq);
if (ret < 0)
goto error;
genlmsg_end(msg, hdr);
return 0;
error:
genlmsg_cancel(msg, hdr);
return -EMSGSIZE;
}
static int psample_nl_cmd_get_group_dumpit(struct sk_buff *msg,
struct netlink_callback *cb)
{
struct psample_group *group;
int start = cb->args[0];
int idx = 0;
int err;
spin_lock_bh(&psample_groups_lock);
list_for_each_entry(group, &psample_groups_list, list) {
if (!net_eq(group->net, sock_net(msg->sk)))
continue;
if (idx < start) {
idx++;
continue;
}
err = psample_group_nl_fill(msg, group, PSAMPLE_CMD_NEW_GROUP,
NETLINK_CB(cb->skb).portid,
cb->nlh->nlmsg_seq, NLM_F_MULTI);
if (err)
break;
idx++;
}
spin_unlock_bh(&psample_groups_lock);
cb->args[0] = idx;
return msg->len;
}
static const struct genl_small_ops psample_nl_ops[] = {
{
.cmd = PSAMPLE_CMD_GET_GROUP,
.validate = GENL_DONT_VALIDATE_STRICT | GENL_DONT_VALIDATE_DUMP,
.dumpit = psample_nl_cmd_get_group_dumpit,
/* can be retrieved by unprivileged users */
}
};
static struct genl_family psample_nl_family __ro_after_init = {
.name = PSAMPLE_GENL_NAME,
.version = PSAMPLE_GENL_VERSION,
.maxattr = PSAMPLE_ATTR_MAX,
.netnsok = true,
.module = THIS_MODULE,
.mcgrps = psample_nl_mcgrps,
.small_ops = psample_nl_ops,
.n_small_ops = ARRAY_SIZE(psample_nl_ops),
.resv_start_op = PSAMPLE_CMD_GET_GROUP + 1,
.n_mcgrps = ARRAY_SIZE(psample_nl_mcgrps),
};
static void psample_group_notify(struct psample_group *group,
enum psample_command cmd)
{
struct sk_buff *msg;
int err;
msg = nlmsg_new(NLMSG_DEFAULT_SIZE, GFP_ATOMIC);
if (!msg)
return;
err = psample_group_nl_fill(msg, group, cmd, 0, 0, NLM_F_MULTI);
if (!err)
genlmsg_multicast_netns(&psample_nl_family, group->net, msg, 0,
PSAMPLE_NL_MCGRP_CONFIG, GFP_ATOMIC);
else
nlmsg_free(msg);
}
static struct psample_group *psample_group_create(struct net *net,
u32 group_num)
{
struct psample_group *group;
group = kzalloc(sizeof(*group), GFP_ATOMIC);
if (!group)
return NULL;
group->net = net;
group->group_num = group_num;
list_add_tail(&group->list, &psample_groups_list);
psample_group_notify(group, PSAMPLE_CMD_NEW_GROUP);
return group;
}
static void psample_group_destroy(struct psample_group *group)
{
psample_group_notify(group, PSAMPLE_CMD_DEL_GROUP);
list_del(&group->list);
kfree_rcu(group, rcu);
}
static struct psample_group *
psample_group_lookup(struct net *net, u32 group_num)
{
struct psample_group *group;
list_for_each_entry(group, &psample_groups_list, list)
if ((group->group_num == group_num) && (group->net == net))
return group;
return NULL;
}
struct psample_group *psample_group_get(struct net *net, u32 group_num)
{
struct psample_group *group;
spin_lock_bh(&psample_groups_lock);
group = psample_group_lookup(net, group_num);
if (!group) {
group = psample_group_create(net, group_num);
if (!group)
goto out;
}
group->refcount++;
out:
spin_unlock_bh(&psample_groups_lock);
return group;
}
EXPORT_SYMBOL_GPL(psample_group_get);
void psample_group_take(struct psample_group *group)
{
spin_lock_bh(&psample_groups_lock);
group->refcount++;
spin_unlock_bh(&psample_groups_lock);
}
EXPORT_SYMBOL_GPL(psample_group_take);
void psample_group_put(struct psample_group *group)
{
spin_lock_bh(&psample_groups_lock);
if (--group->refcount == 0)
psample_group_destroy(group);
spin_unlock_bh(&psample_groups_lock);
}
EXPORT_SYMBOL_GPL(psample_group_put);
#ifdef CONFIG_INET
static int __psample_ip_tun_to_nlattr(struct sk_buff *skb,
struct ip_tunnel_info *tun_info)
{
unsigned short tun_proto = ip_tunnel_info_af(tun_info);
const void *tun_opts = ip_tunnel_info_opts(tun_info);
const struct ip_tunnel_key *tun_key = &tun_info->key;
int tun_opts_len = tun_info->options_len;
if (tun_key->tun_flags & TUNNEL_KEY &&
nla_put_be64(skb, PSAMPLE_TUNNEL_KEY_ATTR_ID, tun_key->tun_id,
PSAMPLE_TUNNEL_KEY_ATTR_PAD))
return -EMSGSIZE;
if (tun_info->mode & IP_TUNNEL_INFO_BRIDGE &&
nla_put_flag(skb, PSAMPLE_TUNNEL_KEY_ATTR_IPV4_INFO_BRIDGE))
return -EMSGSIZE;
switch (tun_proto) {
case AF_INET:
if (tun_key->u.ipv4.src &&
nla_put_in_addr(skb, PSAMPLE_TUNNEL_KEY_ATTR_IPV4_SRC,
tun_key->u.ipv4.src))
return -EMSGSIZE;
if (tun_key->u.ipv4.dst &&
nla_put_in_addr(skb, PSAMPLE_TUNNEL_KEY_ATTR_IPV4_DST,
tun_key->u.ipv4.dst))
return -EMSGSIZE;
break;
case AF_INET6:
if (!ipv6_addr_any(&tun_key->u.ipv6.src) &&
nla_put_in6_addr(skb, PSAMPLE_TUNNEL_KEY_ATTR_IPV6_SRC,
&tun_key->u.ipv6.src))
return -EMSGSIZE;
if (!ipv6_addr_any(&tun_key->u.ipv6.dst) &&
nla_put_in6_addr(skb, PSAMPLE_TUNNEL_KEY_ATTR_IPV6_DST,
&tun_key->u.ipv6.dst))
return -EMSGSIZE;
break;
}
if (tun_key->tos &&
nla_put_u8(skb, PSAMPLE_TUNNEL_KEY_ATTR_TOS, tun_key->tos))
return -EMSGSIZE;
if (nla_put_u8(skb, PSAMPLE_TUNNEL_KEY_ATTR_TTL, tun_key->ttl))
return -EMSGSIZE;
if ((tun_key->tun_flags & TUNNEL_DONT_FRAGMENT) &&
nla_put_flag(skb, PSAMPLE_TUNNEL_KEY_ATTR_DONT_FRAGMENT))
return -EMSGSIZE;
if ((tun_key->tun_flags & TUNNEL_CSUM) &&
nla_put_flag(skb, PSAMPLE_TUNNEL_KEY_ATTR_CSUM))
return -EMSGSIZE;
if (tun_key->tp_src &&
nla_put_be16(skb, PSAMPLE_TUNNEL_KEY_ATTR_TP_SRC, tun_key->tp_src))
return -EMSGSIZE;
if (tun_key->tp_dst &&
nla_put_be16(skb, PSAMPLE_TUNNEL_KEY_ATTR_TP_DST, tun_key->tp_dst))
return -EMSGSIZE;
if ((tun_key->tun_flags & TUNNEL_OAM) &&
nla_put_flag(skb, PSAMPLE_TUNNEL_KEY_ATTR_OAM))
return -EMSGSIZE;
if (tun_opts_len) {
if (tun_key->tun_flags & TUNNEL_GENEVE_OPT &&
nla_put(skb, PSAMPLE_TUNNEL_KEY_ATTR_GENEVE_OPTS,
tun_opts_len, tun_opts))
return -EMSGSIZE;
else if (tun_key->tun_flags & TUNNEL_ERSPAN_OPT &&
nla_put(skb, PSAMPLE_TUNNEL_KEY_ATTR_ERSPAN_OPTS,
tun_opts_len, tun_opts))
return -EMSGSIZE;
}
return 0;
}
static int psample_ip_tun_to_nlattr(struct sk_buff *skb,
struct ip_tunnel_info *tun_info)
{
struct nlattr *nla;
int err;
nla = nla_nest_start_noflag(skb, PSAMPLE_ATTR_TUNNEL);
if (!nla)
return -EMSGSIZE;
err = __psample_ip_tun_to_nlattr(skb, tun_info);
if (err) {
nla_nest_cancel(skb, nla);
return err;
}
nla_nest_end(skb, nla);
return 0;
}
static int psample_tunnel_meta_len(struct ip_tunnel_info *tun_info)
{
unsigned short tun_proto = ip_tunnel_info_af(tun_info);
const struct ip_tunnel_key *tun_key = &tun_info->key;
int tun_opts_len = tun_info->options_len;
int sum = nla_total_size(0); /* PSAMPLE_ATTR_TUNNEL */
if (tun_key->tun_flags & TUNNEL_KEY)
sum += nla_total_size_64bit(sizeof(u64));
if (tun_info->mode & IP_TUNNEL_INFO_BRIDGE)
sum += nla_total_size(0);
switch (tun_proto) {
case AF_INET:
if (tun_key->u.ipv4.src)
sum += nla_total_size(sizeof(u32));
if (tun_key->u.ipv4.dst)
sum += nla_total_size(sizeof(u32));
break;
case AF_INET6:
if (!ipv6_addr_any(&tun_key->u.ipv6.src))
sum += nla_total_size(sizeof(struct in6_addr));
if (!ipv6_addr_any(&tun_key->u.ipv6.dst))
sum += nla_total_size(sizeof(struct in6_addr));
break;
}
if (tun_key->tos)
sum += nla_total_size(sizeof(u8));
sum += nla_total_size(sizeof(u8)); /* TTL */
if (tun_key->tun_flags & TUNNEL_DONT_FRAGMENT)
sum += nla_total_size(0);
if (tun_key->tun_flags & TUNNEL_CSUM)
sum += nla_total_size(0);
if (tun_key->tp_src)
sum += nla_total_size(sizeof(u16));
if (tun_key->tp_dst)
sum += nla_total_size(sizeof(u16));
if (tun_key->tun_flags & TUNNEL_OAM)
sum += nla_total_size(0);
if (tun_opts_len) {
if (tun_key->tun_flags & TUNNEL_GENEVE_OPT)
sum += nla_total_size(tun_opts_len);
else if (tun_key->tun_flags & TUNNEL_ERSPAN_OPT)
sum += nla_total_size(tun_opts_len);
}
return sum;
}
#endif
void psample_sample_packet(struct psample_group *group, struct sk_buff *skb,
u32 sample_rate, const struct psample_metadata *md)
{
ktime_t tstamp = ktime_get_real();
int out_ifindex = md->out_ifindex;
int in_ifindex = md->in_ifindex;
u32 trunc_size = md->trunc_size;
#ifdef CONFIG_INET
struct ip_tunnel_info *tun_info;
#endif
struct sk_buff *nl_skb;
int data_len;
int meta_len;
void *data;
int ret;
meta_len = (in_ifindex ? nla_total_size(sizeof(u16)) : 0) +
(out_ifindex ? nla_total_size(sizeof(u16)) : 0) +
(md->out_tc_valid ? nla_total_size(sizeof(u16)) : 0) +
(md->out_tc_occ_valid ? nla_total_size_64bit(sizeof(u64)) : 0) +
(md->latency_valid ? nla_total_size_64bit(sizeof(u64)) : 0) +
nla_total_size(sizeof(u32)) + /* sample_rate */
nla_total_size(sizeof(u32)) + /* orig_size */
nla_total_size(sizeof(u32)) + /* group_num */
nla_total_size(sizeof(u32)) + /* seq */
nla_total_size_64bit(sizeof(u64)) + /* timestamp */
nla_total_size(sizeof(u16)); /* protocol */
#ifdef CONFIG_INET
tun_info = skb_tunnel_info(skb);
if (tun_info)
meta_len += psample_tunnel_meta_len(tun_info);
#endif
data_len = min(skb->len, trunc_size);
if (meta_len + nla_total_size(data_len) > PSAMPLE_MAX_PACKET_SIZE)
data_len = PSAMPLE_MAX_PACKET_SIZE - meta_len - NLA_HDRLEN
- NLA_ALIGNTO;
nl_skb = genlmsg_new(meta_len + nla_total_size(data_len), GFP_ATOMIC);
if (unlikely(!nl_skb))
return;
data = genlmsg_put(nl_skb, 0, 0, &psample_nl_family, 0,
PSAMPLE_CMD_SAMPLE);
if (unlikely(!data))
goto error;
if (in_ifindex) {
ret = nla_put_u16(nl_skb, PSAMPLE_ATTR_IIFINDEX, in_ifindex);
if (unlikely(ret < 0))
goto error;
}
if (out_ifindex) {
ret = nla_put_u16(nl_skb, PSAMPLE_ATTR_OIFINDEX, out_ifindex);
if (unlikely(ret < 0))
goto error;
}
ret = nla_put_u32(nl_skb, PSAMPLE_ATTR_SAMPLE_RATE, sample_rate);
if (unlikely(ret < 0))
goto error;
ret = nla_put_u32(nl_skb, PSAMPLE_ATTR_ORIGSIZE, skb->len);
if (unlikely(ret < 0))
goto error;
ret = nla_put_u32(nl_skb, PSAMPLE_ATTR_SAMPLE_GROUP, group->group_num);
if (unlikely(ret < 0))
goto error;
ret = nla_put_u32(nl_skb, PSAMPLE_ATTR_GROUP_SEQ, group->seq++);
if (unlikely(ret < 0))
goto error;
if (md->out_tc_valid) {
ret = nla_put_u16(nl_skb, PSAMPLE_ATTR_OUT_TC, md->out_tc);
if (unlikely(ret < 0))
goto error;
}
if (md->out_tc_occ_valid) {
ret = nla_put_u64_64bit(nl_skb, PSAMPLE_ATTR_OUT_TC_OCC,
md->out_tc_occ, PSAMPLE_ATTR_PAD);
if (unlikely(ret < 0))
goto error;
}
if (md->latency_valid) {
ret = nla_put_u64_64bit(nl_skb, PSAMPLE_ATTR_LATENCY,
md->latency, PSAMPLE_ATTR_PAD);
if (unlikely(ret < 0))
goto error;
}
ret = nla_put_u64_64bit(nl_skb, PSAMPLE_ATTR_TIMESTAMP,
ktime_to_ns(tstamp), PSAMPLE_ATTR_PAD);
if (unlikely(ret < 0))
goto error;
ret = nla_put_u16(nl_skb, PSAMPLE_ATTR_PROTO,
be16_to_cpu(skb->protocol));
if (unlikely(ret < 0))
goto error;
if (data_len) {
int nla_len = nla_total_size(data_len);
struct nlattr *nla;
nla = skb_put(nl_skb, nla_len);
nla->nla_type = PSAMPLE_ATTR_DATA;
nla->nla_len = nla_attr_size(data_len);
if (skb_copy_bits(skb, 0, nla_data(nla), data_len))
goto error;
}
#ifdef CONFIG_INET
if (tun_info) {
ret = psample_ip_tun_to_nlattr(nl_skb, tun_info);
if (unlikely(ret < 0))
goto error;
}
#endif
genlmsg_end(nl_skb, data);
genlmsg_multicast_netns(&psample_nl_family, group->net, nl_skb, 0,
PSAMPLE_NL_MCGRP_SAMPLE, GFP_ATOMIC);
return;
error:
pr_err_ratelimited("Could not create psample log message\n");
nlmsg_free(nl_skb);
}
EXPORT_SYMBOL_GPL(psample_sample_packet);
static int __init psample_module_init(void)
{
return genl_register_family(&psample_nl_family);
}
static void __exit psample_module_exit(void)
{
genl_unregister_family(&psample_nl_family);
}
module_init(psample_module_init);
module_exit(psample_module_exit);
MODULE_AUTHOR("Yotam Gigi <yotam.gi@gmail.com>");
MODULE_DESCRIPTION("netlink channel for packet sampling");
MODULE_LICENSE("GPL v2");
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