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Message-Id: <c76311e735fa98af72280a3ef89d22ace28af0e9.1640273966.git.cdleonard@gmail.com>
Date: Thu, 23 Dec 2021 17:40:02 +0200
From: Leonard Crestez <cdleonard@...il.com>
To: David Ahern <dsahern@...nel.org>,
Eric Dumazet <edumazet@...gle.com>,
Philip Paeps <philip@...uble.is>,
Dmitry Safonov <0x7f454c46@...il.com>
Cc: Shuah Khan <shuah@...nel.org>,
"David S. Miller" <davem@...emloft.net>,
Herbert Xu <herbert@...dor.apana.org.au>,
Kuniyuki Iwashima <kuniyu@...zon.co.jp>,
Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
Jakub Kicinski <kuba@...nel.org>,
Yuchung Cheng <ycheng@...gle.com>,
Francesco Ruggeri <fruggeri@...sta.com>,
Mat Martineau <mathew.j.martineau@...ux.intel.com>,
Christoph Paasch <cpaasch@...le.com>,
Ivan Delalande <colona@...sta.com>,
Priyaranjan Jha <priyarjha@...gle.com>, netdev@...r.kernel.org,
linux-crypto@...r.kernel.org, linux-kselftest@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: [PATCH v4 07/19] tcp: authopt: Disable via sysctl by default
This is mainly intended to protect against local privilege escalations
through a rarely used feature so it is deliberately not namespaced.
Enforcement is only at the setsockopt level, this should be enough to
ensure that the tcp_authopt_needed static key never turns on.
No effort is made to handle disabling when the feature is already in
use.
Signed-off-by: Leonard Crestez <cdleonard@...il.com>
---
Documentation/networking/ip-sysctl.rst | 6 ++++
include/net/tcp_authopt.h | 1 +
net/ipv4/sysctl_net_ipv4.c | 39 ++++++++++++++++++++++++++
net/ipv4/tcp_authopt.c | 27 +++++++++++++++++-
4 files changed, 72 insertions(+), 1 deletion(-)
diff --git a/Documentation/networking/ip-sysctl.rst b/Documentation/networking/ip-sysctl.rst
index c04431144f7a..2fa992ef4e02 100644
--- a/Documentation/networking/ip-sysctl.rst
+++ b/Documentation/networking/ip-sysctl.rst
@@ -987,10 +987,16 @@ tcp_limit_output_bytes - INTEGER
tcp_challenge_ack_limit - INTEGER
Limits number of Challenge ACK sent per second, as recommended
in RFC 5961 (Improving TCP's Robustness to Blind In-Window Attacks)
Default: 1000
+tcp_authopt - BOOLEAN
+ Enable the TCP Authentication Option (RFC5925), a replacement for TCP
+ MD5 Signatures (RFC2835).
+
+ Default: 0
+
UDP variables
=============
udp_l3mdev_accept - BOOLEAN
Enabling this option allows a "global" bound socket to work
diff --git a/include/net/tcp_authopt.h b/include/net/tcp_authopt.h
index 7096e3ad59a6..4c9ec1f39932 100644
--- a/include/net/tcp_authopt.h
+++ b/include/net/tcp_authopt.h
@@ -80,10 +80,11 @@ struct tcphdr_authopt {
};
#ifdef CONFIG_TCP_AUTHOPT
DECLARE_STATIC_KEY_FALSE(tcp_authopt_needed_key);
#define tcp_authopt_needed (static_branch_unlikely(&tcp_authopt_needed_key))
+extern int sysctl_tcp_authopt;
void tcp_authopt_free(struct sock *sk, struct tcp_authopt_info *info);
void tcp_authopt_clear(struct sock *sk);
int tcp_set_authopt(struct sock *sk, sockptr_t optval, unsigned int optlen);
int tcp_get_authopt_val(struct sock *sk, struct tcp_authopt *key);
diff --git a/net/ipv4/sysctl_net_ipv4.c b/net/ipv4/sysctl_net_ipv4.c
index 97eb54774924..07de2666314c 100644
--- a/net/ipv4/sysctl_net_ipv4.c
+++ b/net/ipv4/sysctl_net_ipv4.c
@@ -17,10 +17,11 @@
#include <net/udp.h>
#include <net/cipso_ipv4.h>
#include <net/ping.h>
#include <net/protocol.h>
#include <net/netevent.h>
+#include <net/tcp_authopt.h>
static int two = 2;
static int three __maybe_unused = 3;
static int four = 4;
static int thousand = 1000;
@@ -472,10 +473,37 @@ static int proc_fib_multipath_hash_fields(struct ctl_table *table, int write,
return ret;
}
#endif
+#ifdef CONFIG_TCP_AUTHOPT
+static int proc_tcp_authopt(struct ctl_table *ctl,
+ int write, void *buffer, size_t *lenp,
+ loff_t *ppos)
+{
+ int val = sysctl_tcp_authopt;
+ struct ctl_table tmp = {
+ .data = &val,
+ .mode = ctl->mode,
+ .maxlen = sizeof(val),
+ .extra1 = SYSCTL_ZERO,
+ .extra2 = SYSCTL_ONE,
+ };
+ int err;
+
+ err = proc_dointvec_minmax(&tmp, write, buffer, lenp, ppos);
+ if (err)
+ return err;
+ if (sysctl_tcp_authopt && !val) {
+ net_warn_ratelimited("Enabling TCP Authentication Option is permanent\n");
+ return -EINVAL;
+ }
+ sysctl_tcp_authopt = val;
+ return 0;
+}
+#endif
+
static struct ctl_table ipv4_table[] = {
{
.procname = "tcp_max_orphans",
.data = &sysctl_tcp_max_orphans,
.maxlen = sizeof(int),
@@ -583,10 +611,21 @@ static struct ctl_table ipv4_table[] = {
.mode = 0644,
.proc_handler = proc_douintvec_minmax,
.extra1 = &sysctl_fib_sync_mem_min,
.extra2 = &sysctl_fib_sync_mem_max,
},
+#ifdef CONFIG_TCP_AUTHOPT
+ {
+ .procname = "tcp_authopt",
+ .data = &sysctl_tcp_authopt,
+ .maxlen = sizeof(int),
+ .mode = 0644,
+ .proc_handler = proc_tcp_authopt,
+ .extra1 = SYSCTL_ZERO,
+ .extra2 = SYSCTL_ONE,
+ },
+#endif
{ }
};
static struct ctl_table ipv4_net_table[] = {
{
diff --git a/net/ipv4/tcp_authopt.c b/net/ipv4/tcp_authopt.c
index ba20a70359ee..6be5dbcd530e 100644
--- a/net/ipv4/tcp_authopt.c
+++ b/net/ipv4/tcp_authopt.c
@@ -4,10 +4,15 @@
#include <net/ipv6.h>
#include <net/tcp.h>
#include <linux/kref.h>
#include <crypto/hash.h>
+/* This is mainly intended to protect against local privilege escalations through
+ * a rarely used feature so it is deliberately not namespaced.
+ */
+int sysctl_tcp_authopt;
+
/* This is enabled when first struct tcp_authopt_info is allocated and never released */
DEFINE_STATIC_KEY_FALSE(tcp_authopt_needed_key);
EXPORT_SYMBOL(tcp_authopt_needed_key);
/* All current algorithms have a mac length of 12 but crypto API digestsize can be larger */
@@ -425,17 +430,30 @@ static int _copy_from_sockptr_tolerant(u8 *dst,
memset(dst + srclen, 0, dstlen - srclen);
return err;
}
+static int check_sysctl_tcp_authopt(void)
+{
+ if (!sysctl_tcp_authopt) {
+ net_warn_ratelimited("TCP Authentication Option disabled by sysctl.\n");
+ return -EPERM;
+ }
+
+ return 0;
+}
+
int tcp_set_authopt(struct sock *sk, sockptr_t optval, unsigned int optlen)
{
struct tcp_authopt opt;
struct tcp_authopt_info *info;
int err;
sock_owned_by_me(sk);
+ err = check_sysctl_tcp_authopt();
+ if (err)
+ return err;
err = _copy_from_sockptr_tolerant((u8 *)&opt, sizeof(opt), optval, optlen);
if (err)
return err;
@@ -453,14 +471,18 @@ int tcp_set_authopt(struct sock *sk, sockptr_t optval, unsigned int optlen)
int tcp_get_authopt_val(struct sock *sk, struct tcp_authopt *opt)
{
struct tcp_sock *tp = tcp_sk(sk);
struct tcp_authopt_info *info;
+ int err;
+ memset(opt, 0, sizeof(*opt));
sock_owned_by_me(sk);
+ err = check_sysctl_tcp_authopt();
+ if (err)
+ return err;
- memset(opt, 0, sizeof(*opt));
info = rcu_dereference_check(tp->authopt_info, lockdep_sock_is_held(sk));
if (!info)
return -ENOENT;
opt->flags = info->flags & TCP_AUTHOPT_KNOWN_FLAGS;
@@ -481,10 +503,13 @@ int tcp_set_authopt_key(struct sock *sk, sockptr_t optval, unsigned int optlen)
struct netns_tcp_authopt *net = sock_net_tcp_authopt(sk);
struct tcp_authopt_alg_imp *alg;
int err;
sock_owned_by_me(sk);
+ err = check_sysctl_tcp_authopt();
+ if (err)
+ return err;
if (!ns_capable(sock_net(sk)->user_ns, CAP_NET_ADMIN))
return -EPERM;
err = _copy_from_sockptr_tolerant((u8 *)&opt, sizeof(opt), optval, optlen);
if (err)
--
2.25.1
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