Re: [PATCH v2 09/25] tcp: authopt: Disable via sysctl by default

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On 11/3/21 4:39 AM, David Ahern wrote:
On 11/1/21 10:34 AM, Leonard Crestez wrote:
diff --git a/net/ipv4/sysctl_net_ipv4.c b/net/ipv4/sysctl_net_ipv4.c
index 97eb54774924..cc34de6e4817 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;
@@ -583,10 +584,19 @@ 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_dointvec,

Just add it to the namespace set, and this could be a u8 (try to plug a
hole if possible) with min/max specified:

                 .maxlen         = sizeof(u8),
                 .mode           = 0644,
                 .extra1         = SYSCTL_ZERO,
                 .extra2         = SYSCTL_ONE


see icmp_echo_enable_probe as an example. And if you are not going to
clean up when toggled off, you need a handler that tells the user it can
not be disabled by erroring out on attempts to disable it.

This is deliberately per-system because the goal is to avoid possible local privilege escalations by reducing the attack surface. Even the smallest flaw could be exploited by a malicious application establishing an authenticated connection on loopback.

Applications running in containers frequently have full access to sysctls so making this per-namespace would defeat the original purpose. I can't think of any reason to prevent using this feature at the namespace level, it has no interesting effects outside TCP connections for which it is enabled.

I also believe that as similar sysctl would be useful for TCP-MD5.

You're right about adding additional prints.

--
Regards,
Leonard



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