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diff --git a/share/man/man4/tcp.4 b/share/man/man4/tcp.4
--- a/share/man/man4/tcp.4
+++ b/share/man/man4/tcp.4
@@ -31,7 +31,7 @@
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
.\" SUCH DAMAGE.
.\"
-.Dd August 3, 2024
+.Dd January 10, 2025
.Dt TCP 4
.Os
.Sh NAME
@@ -200,6 +200,35 @@
To list the available TCP stacks, see
.Va functions_available
in the
+.Sx FIB support
+TCP sockets are FIB-aware.
+They inherit the FIB of the process which created the socket, or that of the
+listening socket for sockets created by
+.Xr accept 2 .
+In particular, the FIB is not inherited from that of the interface where the
+initiating SYN packet was received.
+When an incoming connection request arrives to a listening socket, the initial
+handshake also occurs in the FIB of the listening socket, not that of the
+received packet.
+.Pp
+By default, a TCP listening socket can accept connections originating from any
+FIB.
+If the
+.Va net.inet.tcp.bind_all_fibs
+tunable is set to 0, a listening socket will only accept connections
+originating
+from the FIB's listening socket.
+Connection requests from other FIBs will be treated as though there is no
+listening socket for the destination address and port.
+In this mode, multiple listening sockets owned by the same user can listen on
+the same address and port so long as they belong to different FIBs, similar to
+the behavior of the
+.Dv SO_REUSEPORT
+socket option.
+If the tunable is set to 0, all sockets added to a load-balancing group created
+with the
+.Dv SO_REUSEPORT_LB
+socket option must belong to the same FIB.
.Sx MIB (sysctl) Variables
section further down.
To list the default TCP stack, see
@@ -1041,6 +1070,7 @@
.El
.Sh SEE ALSO
.Xr getsockopt 2 ,
+.Xr setfib 2 ,
.Xr socket 2 ,
.Xr stats 3 ,
.Xr sysctl 3 ,
diff --git a/sys/netinet/tcp_input.c b/sys/netinet/tcp_input.c
--- a/sys/netinet/tcp_input.c
+++ b/sys/netinet/tcp_input.c
@@ -135,6 +135,11 @@
&VNET_NAME(tcp_log_in_vain), 0,
"Log all incoming TCP segments to closed ports");
+VNET_DEFINE(int, tcp_bind_all_fibs) = 1;
+SYSCTL_INT(_net_inet_tcp, OID_AUTO, bind_all_fibs, CTLFLAG_VNET | CTLFLAG_RDTUN,
+ &VNET_NAME(tcp_bind_all_fibs), 0,
+ "Bound sockets receive traffic from all FIBs");
+
VNET_DEFINE(int, blackhole) = 0;
#define V_blackhole VNET(blackhole)
SYSCTL_INT(_net_inet_tcp, OID_AUTO, blackhole, CTLFLAG_VNET | CTLFLAG_RW,
@@ -833,7 +838,8 @@
*/
lookupflag = INPLOOKUP_WILDCARD |
((thflags & (TH_ACK|TH_SYN)) == TH_SYN ?
- INPLOOKUP_RLOCKPCB : INPLOOKUP_WLOCKPCB);
+ INPLOOKUP_RLOCKPCB : INPLOOKUP_WLOCKPCB) |
+ (V_tcp_bind_all_fibs ? 0 : INPLOOKUP_FIB);
findpcb:
tp = NULL;
#ifdef INET6
diff --git a/sys/netinet/tcp_usrreq.c b/sys/netinet/tcp_usrreq.c
--- a/sys/netinet/tcp_usrreq.c
+++ b/sys/netinet/tcp_usrreq.c
@@ -262,7 +262,8 @@
goto out;
}
INP_HASH_WLOCK(&V_tcbinfo);
- error = in_pcbbind(inp, sinp, 0, td->td_ucred);
+ error = in_pcbbind(inp, sinp, V_tcp_bind_all_fibs ? 0 : INPBIND_FIB,
+ td->td_ucred);
INP_HASH_WUNLOCK(&V_tcbinfo);
out:
tcp_bblog_pru(tp, PRU_BIND, error);
@@ -336,7 +337,8 @@
}
}
#endif
- error = in6_pcbbind(inp, sin6, 0, td->td_ucred);
+ error = in6_pcbbind(inp, sin6, V_tcp_bind_all_fibs ? 0 : INPBIND_FIB,
+ td->td_ucred);
INP_HASH_WUNLOCK(&V_tcbinfo);
out:
if (error != 0)
@@ -378,7 +380,8 @@
}
if (inp->inp_lport == 0) {
INP_HASH_WLOCK(&V_tcbinfo);
- error = in_pcbbind(inp, NULL, 0, td->td_ucred);
+ error = in_pcbbind(inp, NULL,
+ V_tcp_bind_all_fibs ? 0 : INPBIND_FIB, td->td_ucred);
INP_HASH_WUNLOCK(&V_tcbinfo);
}
if (error == 0) {
@@ -441,7 +444,8 @@
inp->inp_vflag &= ~INP_IPV4;
if ((inp->inp_flags & IN6P_IPV6_V6ONLY) == 0)
inp->inp_vflag |= INP_IPV4;
- error = in6_pcbbind(inp, NULL, 0, td->td_ucred);
+ error = in6_pcbbind(inp, NULL,
+ V_tcp_bind_all_fibs ? 0 : INPBIND_FIB, td->td_ucred);
}
INP_HASH_WUNLOCK(&V_tcbinfo);
if (error == 0) {
diff --git a/sys/netinet/tcp_var.h b/sys/netinet/tcp_var.h
--- a/sys/netinet/tcp_var.h
+++ b/sys/netinet/tcp_var.h
@@ -1271,6 +1271,7 @@
VNET_DECLARE(int, tcp_autorcvbuf_max);
VNET_DECLARE(int, tcp_autosndbuf_inc);
VNET_DECLARE(int, tcp_autosndbuf_max);
+VNET_DECLARE(int, tcp_bind_all_fibs);
VNET_DECLARE(int, tcp_delack_enabled);
VNET_DECLARE(int, tcp_do_autorcvbuf);
VNET_DECLARE(int, tcp_do_autosndbuf);
@@ -1324,6 +1325,7 @@
#define V_tcp_autorcvbuf_max VNET(tcp_autorcvbuf_max)
#define V_tcp_autosndbuf_inc VNET(tcp_autosndbuf_inc)
#define V_tcp_autosndbuf_max VNET(tcp_autosndbuf_max)
+#define V_tcp_bind_all_fibs VNET(tcp_bind_all_fibs)
#define V_tcp_delack_enabled VNET(tcp_delack_enabled)
#define V_tcp_do_autorcvbuf VNET(tcp_do_autorcvbuf)
#define V_tcp_do_autosndbuf VNET(tcp_do_autosndbuf)

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