internal/netlink: set receive buffer size

This is done by both systemd sd-device and AOSP ueventd to improve robustness. Rosa OS will still handle ENOBUFS via coldboot but a big buffer should mitigate this as well.

Signed-off-by: Ophestra <cat@gensokyo.uk>

5 files changed, 29 insertions, 8 deletions

diff --git a/container/dispatcher.go b/container/dispatcher.go
index 9f971fa5..d3ff4f00 100644
--- a/container/dispatcher.go
+++ b/container/dispatcher.go
@@ -179,7 +179,7 @@ func (direct) mustLoopback(ctx context.Context, msg message.Msg) {
 		lo = ifi.Index
 	}
 
-	c, err := netlink.DialRoute()
+	c, err := netlink.DialRoute(0)
 	if err != nil {
 		msg.GetLogger().Fatalln(err)
 	}
diff --git a/internal/netlink/netlink.go b/internal/netlink/netlink.go
index 7324f1a7..6cd15610 100644
--- a/internal/netlink/netlink.go
+++ b/internal/netlink/netlink.go
@@ -46,7 +46,11 @@ type Conn struct {
 
 // Dial returns the address of a newly connected generic netlink connection of
 // specified family and groups.
-func Dial(family int, groups uint32) (*Conn, error) {
+//
+// For a nonzero rcvbuf, the socket receive buffer size is set to its absolute
+// value via SO_RCVBUF for a positive value, or SO_RCVBUFFORCE for a negative
+// value.
+func Dial(family int, groups uint32, rcvbuf int64) (*Conn, error) {
 	var c Conn
 	if fd, err := syscall.Socket(
 		syscall.AF_NETLINK,
@@ -75,6 +79,23 @@ func Dial(family int, groups uint32) (*Conn, error) {
 			return nil, syscall.ENOTRECOVERABLE
 		}
 
+		if rcvbuf != 0 {
+			opt := syscall.SO_RCVBUF
+			if rcvbuf < 0 {
+				opt = syscall.SO_RCVBUFFORCE
+				rcvbuf = -rcvbuf
+			}
+			if err = syscall.SetsockoptInt(
+				fd,
+				syscall.SOL_SOCKET,
+				opt,
+				int(rcvbuf),
+			); err != nil {
+				_ = syscall.Close(fd)
+				return nil, os.NewSyscallError("setsockopt", err)
+			}
+		}
+
 		c.family = family
 		c.f = os.NewFile(uintptr(fd), "netlink")
 		if c.raw, err = c.f.SyscallConn(); err != nil {
diff --git a/internal/netlink/rtnl.go b/internal/netlink/rtnl.go
index e370bae7..521e8569 100644
--- a/internal/netlink/rtnl.go
+++ b/internal/netlink/rtnl.go
@@ -13,8 +13,8 @@ type RouteConn struct{ conn *Conn }
 func (c *RouteConn) Close() error { return c.conn.Close() }
 
 // DialRoute returns the address of a newly connected [RouteConn].
-func DialRoute() (*RouteConn, error) {
-	c, err := Dial(syscall.NETLINK_ROUTE, 0)
+func DialRoute(rcvbuf int64) (*RouteConn, error) {
+	c, err := Dial(syscall.NETLINK_ROUTE, 0, rcvbuf)
 	if err != nil {
 		return nil, err
 	}
diff --git a/internal/uevent/uevent.go b/internal/uevent/uevent.go
index 47091f59..25fd02be 100644
--- a/internal/uevent/uevent.go
+++ b/internal/uevent/uevent.go
@@ -50,9 +50,9 @@ func (c *Conn) exitExcl() { c.excl.Store(false) }
 func (c *Conn) Close() error { return c.conn.Close() }
 
 // Dial returns the address of a newly connected [Conn].
-func Dial() (*Conn, error) {
+func Dial(rcvbuf int64) (*Conn, error) {
 	// kernel group is hard coded in lib/kobject_uevent.c, undocumented
-	c, err := netlink.Dial(syscall.NETLINK_KOBJECT_UEVENT, 1)
+	c, err := netlink.Dial(syscall.NETLINK_KOBJECT_UEVENT, 1, rcvbuf)
 	if err != nil {
 		return nil, err
 	}
diff --git a/internal/uevent/uevent_test.go b/internal/uevent/uevent_test.go
index 7dce4798..9b986ff3 100644
--- a/internal/uevent/uevent_test.go
+++ b/internal/uevent/uevent_test.go
@@ -116,7 +116,7 @@ func adeB[V any, S interface {
 func TestDialConsume(t *testing.T) {
 	t.Parallel()
 
-	c, err := uevent.Dial()
+	c, err := uevent.Dial(0)
 	if err != nil {
 		t.Fatalf("Dial: error = %v", err)
 	}
@@ -127,7 +127,7 @@ func TestDialConsume(t *testing.T) {
 	})
 
 	// check kernel-assigned port id
-	c0, err0 := uevent.Dial()
+	c0, err0 := uevent.Dial(0)
 	if err0 != nil {
 		t.Fatalf("Dial: error = %v", err)
 	}