From 81ecd8b6eab7457b331762626f8c210fec3504e6 Mon Sep 17 00:00:00 2001
From: Ian Gudger <igudger@google.com>
Date: Mon, 29 Apr 2019 21:20:05 -0700
Subject: Implement the MSG_CTRUNC msghdr flag for Unix sockets.

Updates google/gvisor#206

PiperOrigin-RevId: 245880573
Change-Id: Ifa715e98d47f64b8a32b04ae9378d6cd6bd4025e
---
 pkg/sentry/socket/unix/unix.go | 13 +++++++++++++
 1 file changed, 13 insertions(+)

(limited to 'pkg/sentry/socket/unix/unix.go')

diff --git a/pkg/sentry/socket/unix/unix.go b/pkg/sentry/socket/unix/unix.go
index e9607aa01..26788ec31 100644
--- a/pkg/sentry/socket/unix/unix.go
+++ b/pkg/sentry/socket/unix/unix.go
@@ -490,6 +490,9 @@ func (s *SocketOperations) RecvMsg(t *kernel.Task, dst usermem.IOSequence, flags
 	if s.Passcred() {
 		// Credentials take priority if they are enabled and there is space.
 		wantCreds = rightsLen > 0
+		if !wantCreds {
+			msgFlags |= linux.MSG_CTRUNC
+		}
 		credLen := syscall.CmsgSpace(syscall.SizeofUcred)
 		rightsLen -= credLen
 	}
@@ -516,6 +519,10 @@ func (s *SocketOperations) RecvMsg(t *kernel.Task, dst usermem.IOSequence, flags
 			from, fromLen = epsocket.ConvertAddress(linux.AF_UNIX, *r.From)
 		}
 
+		if r.ControlTrunc {
+			msgFlags |= linux.MSG_CTRUNC
+		}
+
 		if err != nil || dontWait || !waitAll || s.isPacket || n >= dst.NumBytes() {
 			if s.isPacket && n < int64(r.MsgSize) {
 				msgFlags |= linux.MSG_TRUNC
@@ -546,12 +553,18 @@ func (s *SocketOperations) RecvMsg(t *kernel.Task, dst usermem.IOSequence, flags
 			if r.From != nil {
 				from, fromLen = epsocket.ConvertAddress(linux.AF_UNIX, *r.From)
 			}
+
+			if r.ControlTrunc {
+				msgFlags |= linux.MSG_CTRUNC
+			}
+
 			if trunc {
 				// n and r.MsgSize are the same for streams.
 				total += int64(r.MsgSize)
 			} else {
 				total += n
 			}
+
 			if err != nil || !waitAll || s.isPacket || n >= dst.NumBytes() {
 				if total > 0 {
 					err = nil
-- 
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