Currently, outbound forwards (-T, -U) are handled by sockets bound to the
loopback address. Typically we create two sockets, one for 127.0.0.1 and
one for ::1.
This has some disadvantages:
* The guest can't connect via 127.0.0.0/8 addresses other than 127.0.0.1
* We can't use dual-stack sockets, we have to have separate sockets for
IPv4 and IPv6.
The restriction exists for a reason though. If the guest has any
interfaces other than pasta (e.g. a VPN tunnel) external hosts could reach
the host via the forwards. Especially combined with -T auto / -U auto this
would make it very easy to make a mistake with nasty security implications.
We can achieve this a different way, however. Don't bind to a specific
address, but _do_ use SO_BINDTODEVICE to restrict the sockets to the "lo"
interface. We fall back to the old behaviour for older kernels where
SO_BINDTODEVICE is not available unprivileged.
Note that although traffic to a local but non-loopback address is passed
over the 'lo' interface (as seen by netfilter and dumpcap), it doesn't
count as attached to that interface for the purposes of SO_BINDTODEVICE
(information from the routing table overrides the "physical" interface).
So, this change doesn't help for bug 100.
It's also not a complete fix for bug 113, it does however:
* Get us a step closer to fixing bug 113
* Slightly simplify the code
* Make things a bit easier to allow more flexible binding on the guest in
in future
Link: https://bugs.passt.top/show_bug.cgi?id=113
Signed-off-by: David Gibson
---
conf.c | 6 ++++++
pif.c | 6 ------
tcp.c | 5 +++++
udp.c | 30 +++++++++++++++++++++++-------
4 files changed, 34 insertions(+), 13 deletions(-)
diff --git a/conf.c b/conf.c
index 6bd9717b..02a4b65a 100644
--- a/conf.c
+++ b/conf.c
@@ -235,6 +235,12 @@ static void conf_ports(const struct ctx *c, char optname, const char *optarg,
if (c->mode != MODE_PASTA)
die("'auto' port forwarding is only allowed for pasta");
+ if ((optname == 'T' || optname == 'U') && c->no_bindtodevice) {
+ warn(
+"'-%c auto' enabled without unprivileged SO_BINDTODEVICE", optname);
+ warn(
+"Forwarding from addresses other than 127.0.0.1 will not work");
+ }
fwd->mode = FWD_AUTO;
return;
}
diff --git a/pif.c b/pif.c
index 85904f35..db447b4f 100644
--- a/pif.c
+++ b/pif.c
@@ -81,12 +81,6 @@ int pif_sock_l4(const struct ctx *c, enum epoll_type type, uint8_t pif,
ASSERT(pif_is_socket(pif));
- if (pif == PIF_SPLICE) {
- /* Sanity checks */
- ASSERT(!ifname);
- ASSERT(addr && inany_is_loopback(addr));
- }
-
if (!addr) {
ref.fd = sock_l4_dualstack(c, type, port, ifname);
} else {
diff --git a/tcp.c b/tcp.c
index 2abb8be4..aacc5b20 100644
--- a/tcp.c
+++ b/tcp.c
@@ -2627,6 +2627,11 @@ static void tcp_ns_sock_init(const struct ctx *c, in_port_t port)
{
ASSERT(!c->no_tcp);
+ if (!c->no_bindtodevice) {
+ tcp_sock_init(c, PIF_SPLICE, NULL, "lo", port);
+ return;
+ }
+
if (c->ifi4)
tcp_sock_init_one(c, PIF_SPLICE, &inany_loopback4, NULL, port);
if (c->ifi6)
diff --git a/udp.c b/udp.c
index 3d097fbb..4b625b78 100644
--- a/udp.c
+++ b/udp.c
@@ -1182,6 +1182,26 @@ static void udp_splice_iov_init(void)
}
}
+/**
+ * udp_ns_sock_init() - Init socket to listen for spliced outbound connections
+ * @c: Execution context
+ * @port: Port, host order
+ */
+static void udp_ns_sock_init(const struct ctx *c, in_port_t port)
+{
+ ASSERT(!c->no_udp);
+
+ if (!c->no_bindtodevice) {
+ udp_sock_init(c, PIF_SPLICE, NULL, "lo", port);
+ return;
+ }
+
+ if (c->ifi4)
+ udp_sock_init(c, PIF_SPLICE, &inany_loopback4, NULL, port);
+ if (c->ifi6)
+ udp_sock_init(c, PIF_SPLICE, &inany_loopback6, NULL, port);
+}
+
/**
* udp_port_rebind() - Rebind ports to match forward maps
* @c: Execution context
@@ -1213,14 +1233,10 @@ static void udp_port_rebind(struct ctx *c, bool outbound)
if ((c->ifi4 && socks[V4][port] == -1) ||
(c->ifi6 && socks[V6][port] == -1)) {
- if (outbound) {
- udp_sock_init(c, PIF_SPLICE,
- &inany_loopback4, NULL, port);
- udp_sock_init(c, PIF_SPLICE,
- &inany_loopback6, NULL, port);
- } else {
+ if (outbound)
+ udp_ns_sock_init(c, port);
+ else
udp_sock_init(c, PIF_HOST, NULL, NULL, port);
- }
}
}
}
--
2.52.0