Fix error handling on fusefs mount.

Don't propagate arbitrary golang errors up from fusefs because errors
that don't map to an errno result in a sentry panic.

Reported-by: syzbot+697cb635346e456fddfc@syzkaller.appspotmail.com
PiperOrigin-RevId: 346220306

3 files changed, 58 insertions, 0 deletions

diff --git a/test/fuse/BUILD b/test/fuse/BUILD
index 8e31fdd41..74500ec84 100644
--- a/test/fuse/BUILD
+++ b/test/fuse/BUILD
@@ -71,3 +71,8 @@ syscall_test(
     fuse = "True",
     test = "//test/fuse/linux:setstat_test",
 )
+
+syscall_test(
+    fuse = "True",
+    test = "//test/fuse/linux:mount_test",
+)
diff --git a/test/fuse/linux/BUILD b/test/fuse/linux/BUILD
index 7673252ec..d1fb178e8 100644
--- a/test/fuse/linux/BUILD
+++ b/test/fuse/linux/BUILD
@@ -228,3 +228,15 @@ cc_binary(
         "//test/util:test_util",
     ],
 )
+
+cc_binary(
+    name = "mount_test",
+    testonly = 1,
+    srcs = ["mount_test.cc"],
+    deps = [
+        gtest,
+        "//test/util:temp_path",
+        "//test/util:test_main",
+        "//test/util:test_util",
+    ],
+)
diff --git a/test/fuse/linux/mount_test.cc b/test/fuse/linux/mount_test.cc
new file mode 100644
index 000000000..a5c2fbb01
--- /dev/null
+++ b/test/fuse/linux/mount_test.cc
@@ -0,0 +1,41 @@
+// Copyright 2020 The gVisor Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include <errno.h>
+#include <fcntl.h>
+#include <sys/mount.h>
+
+#include "gtest/gtest.h"
+#include "test/util/temp_path.h"
+#include "test/util/test_util.h"
+
+namespace gvisor {
+namespace testing {
+
+namespace {
+
+TEST(FuseMount, FDNotParsable) {
+  int devfd;
+  EXPECT_THAT(devfd = open("/dev/fuse", O_RDWR), SyscallSucceeds());
+  std::string mount_opts = "fd=thiscantbeparsed";
+  TempPath mount_dir = ASSERT_NO_ERRNO_AND_VALUE(TempPath::CreateDir());
+  EXPECT_THAT(mount("fuse", mount_dir.path().c_str(), "fuse",
+                    MS_NODEV | MS_NOSUID, mount_opts.c_str()),
+              SyscallFailsWithErrno(EINVAL));
+}
+
+}  // namespace
+
+}  // namespace testing
+}  // namespace gvisor