Index: projects/fuse2/tests/sys/fs/fusefs/allow_other.cc
===================================================================
--- projects/fuse2/tests/sys/fs/fusefs/allow_other.cc	(revision 345735)
+++ projects/fuse2/tests/sys/fs/fusefs/allow_other.cc	(revision 345736)
@@ -1,114 +1,181 @@
 /*-
  * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
  *
  * Copyright (c) 2019 The FreeBSD Foundation
  *
  * This software was developed by BFF Storage Systems, LLC under sponsorship
  * from the FreeBSD Foundation.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
  *    documentation and/or other materials provided with the distribution.
  *
  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  * SUCH DAMAGE.
  */
 
 /*
  * Tests for the "allow_other" mount option.  They must be in their own
  * file so they can be run as root
  */
 
 extern "C" {
 #include <sys/types.h>
 #include <fcntl.h>
 #include <unistd.h>
 }
 
 #include "mockfs.hh"
 #include "utils.hh"
 
 using namespace testing;
 
 const static char FULLPATH[] = "mountpoint/some_file.txt";
 const static char RELPATH[] = "some_file.txt";
 
 class NoAllowOther: public FuseTest {
 
 public:
 /* Unprivileged user id */
 int m_uid;
 
 virtual void SetUp() {
 	if (geteuid() != 0) {
 		GTEST_SKIP() << "This test must be run as root";
 	}
 
 	FuseTest::SetUp();
 }
 };
 
 class AllowOther: public NoAllowOther {
 
 public:
 virtual void SetUp() {
 	m_allow_other = true;
 	NoAllowOther::SetUp();
 }
 };
 
 TEST_F(AllowOther, allowed)
 {
 	fork(true, [&] {
 			uint64_t ino = 42;
 
 			expect_lookup(RELPATH, ino, S_IFREG | 0644, 0, 1);
 			expect_open(ino, 0, 1);
 			expect_release(ino, FH);
 			expect_getattr(ino, 0);
 		}, []() {
 			int fd;
 
 			fd = open(FULLPATH, O_RDONLY);
 			if (fd < 0) {
 				perror("open");
 				return(1);
 			}
 			return 0;
 		}
 	);
 }
 
+/*
+ * A variation of the Open.multiple_creds test showing how the bug can lead to a
+ * privilege elevation.  The first process is privileged and opens a file only
+ * visible to root.  The second process is unprivileged and shouldn't be able
+ * to open the file, but does thanks to the bug
+ */
+/* https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=236844 */
+TEST_F(AllowOther, DISABLED_privilege_escalation)
+{
+	const static char FULLPATH[] = "mountpoint/some_file.txt";
+	const static char RELPATH[] = "some_file.txt";
+	int fd1;
+	const static uint64_t ino = 42;
+	const static uint64_t fh = 100;
+
+	/* Fork a child to open the file with different credentials */
+	fork(true, [&] {
+
+		expect_lookup(RELPATH, ino, S_IFREG | 0600, 0, 2);
+		EXPECT_CALL(*m_mock, process(
+			ResultOf([=](auto in) {
+				return (in->header.opcode == FUSE_OPEN &&
+					in->header.pid == (uint32_t)getpid() &&
+					in->header.uid == (uint32_t)geteuid() &&
+					in->header.nodeid == ino);
+			}, Eq(true)),
+			_)
+		).WillOnce(Invoke(
+			ReturnImmediate([](auto in __unused, auto out) {
+			out->body.open.fh = fh;
+			out->header.len = sizeof(out->header);
+			SET_OUT_HEADER_LEN(out, open);
+		})));
+
+		EXPECT_CALL(*m_mock, process(
+			ResultOf([=](auto in) {
+				return (in->header.opcode == FUSE_OPEN &&
+					in->header.pid != (uint32_t)getpid() &&
+					in->header.uid != (uint32_t)geteuid() &&
+					in->header.nodeid == ino);
+			}, Eq(true)),
+			_)
+		).Times(AnyNumber())
+		.WillRepeatedly(Invoke(ReturnErrno(EPERM)));
+		expect_getattr(ino, 0);
+
+		fd1 = open(FULLPATH, O_RDONLY);
+		EXPECT_LE(0, fd1) << strerror(errno);
+	}, [] {
+		int fd0;
+
+		fd0 = open(FULLPATH, O_RDONLY);
+		if (fd0 >= 0) {
+			fprintf(stderr, "Privilege escalation!\n");
+			return 1;
+		}
+		if (errno != EPERM) {
+			fprintf(stderr, "Unexpected error %s\n",
+				strerror(errno));
+			return 1;
+		}
+		return 0;
+	}
+	);
+	/* Deliberately leak fd1.  close(2) will be tested in release.cc */
+}
+
 TEST_F(NoAllowOther, disallowed)
 {
 	fork(true, [] {
 		}, []() {
 			int fd;
 
 			fd = open(FULLPATH, O_RDONLY);
 			if (fd >= 0) {
 				fprintf(stderr, "open should've failed\n");
 				return(1);
 			} else if (errno != EPERM) {
 				fprintf(stderr, "Unexpected error: %s\n",
 					strerror(errno));
 				return(1);
 			}
 			return 0;
 		}
 	);
 }