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Date:      Tue, 03 Sep 2019 14:06:02 -0000
From:      Alan Somers <asomers@FreeBSD.org>
To:        src-committers@freebsd.org, svn-src-projects@freebsd.org
Subject:   svn commit: r345736 - projects/fuse2/tests/sys/fs/fusefs
Message-ID:  <201903301724.x2UHOC0H008936@repo.freebsd.org>
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Author: asomers
Date: Sat Mar 30 17:24:11 2019
New Revision: 345736
URL: https://svnweb.freebsd.org/changeset/base/345736

Log:
  fusefs: add another regression test for bug 236844
  
  This test shows how bug 236844 can lead to a privilege escalation when used
  with the -o allow_other mount option.
  
  PR:		236844
  Sponsored by:	The FreeBSD Foundation

Modified:
  projects/fuse2/tests/sys/fs/fusefs/allow_other.cc

Modified: projects/fuse2/tests/sys/fs/fusefs/allow_other.cc
==============================================================================
--- projects/fuse2/tests/sys/fs/fusefs/allow_other.cc	Sat Mar 30 17:23:15 2019	(r345735)
+++ projects/fuse2/tests/sys/fs/fusefs/allow_other.cc	Sat Mar 30 17:24:11 2019	(r345736)
@@ -93,6 +93,73 @@ TEST_F(AllowOther, allowed)
 	);
 }
 
+/*
+ * 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, [] {

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