Check that a file is a regular file with open(O_TRUNC).

It was possible to panic the sentry by opening a cache revalidating folder with
O_TRUNC|O_CREAT.

Avoids breaking php tests.

PiperOrigin-RevId: 280533213

5 files changed, 77 insertions, 2 deletions

diff --git a/test/syscalls/linux/open.cc b/test/syscalls/linux/open.cc
index 2b1df52ce..267ae19f6 100644
--- a/test/syscalls/linux/open.cc
+++ b/test/syscalls/linux/open.cc
@@ -73,6 +73,28 @@ class OpenTest : public FileTest {
   const std::string test_data_ = "hello world\n";
 };
 
+TEST_F(OpenTest, OTrunc) {
+  auto dirpath = JoinPath(GetAbsoluteTestTmpdir(), "truncd");
+  ASSERT_THAT(mkdir(dirpath.c_str(), 0777), SyscallSucceeds());
+  ASSERT_THAT(open(dirpath.c_str(), O_TRUNC, 0666),
+              SyscallFailsWithErrno(EISDIR));
+}
+
+TEST_F(OpenTest, OTruncAndReadOnlyDir) {
+  auto dirpath = JoinPath(GetAbsoluteTestTmpdir(), "truncd");
+  ASSERT_THAT(mkdir(dirpath.c_str(), 0777), SyscallSucceeds());
+  ASSERT_THAT(open(dirpath.c_str(), O_TRUNC | O_RDONLY, 0666),
+              SyscallFailsWithErrno(EISDIR));
+}
+
+TEST_F(OpenTest, OTruncAndReadOnlyFile) {
+  auto dirpath = JoinPath(GetAbsoluteTestTmpdir(), "truncfile");
+  const FileDescriptor existing =
+      ASSERT_NO_ERRNO_AND_VALUE(Open(dirpath.c_str(), O_RDWR | O_CREAT, 0666));
+  const FileDescriptor otrunc = ASSERT_NO_ERRNO_AND_VALUE(
+      Open(dirpath.c_str(), O_TRUNC | O_RDONLY, 0666));
+}
+
 TEST_F(OpenTest, ReadOnly) {
   char buf;
   const FileDescriptor ro_file =
diff --git a/test/syscalls/linux/open_create.cc b/test/syscalls/linux/open_create.cc
index e5a85ef9d..431733dbe 100644
--- a/test/syscalls/linux/open_create.cc
+++ b/test/syscalls/linux/open_create.cc
@@ -88,6 +88,30 @@ TEST(CreateTest, CreateExclusively) {
               SyscallFailsWithErrno(EEXIST));
 }
 
+TEST(CreateTeast, CreatWithOTrunc) {
+  std::string dirpath = JoinPath(GetAbsoluteTestTmpdir(), "truncd");
+  ASSERT_THAT(mkdir(dirpath.c_str(), 0777), SyscallSucceeds());
+  ASSERT_THAT(open(dirpath.c_str(), O_CREAT | O_TRUNC, 0666),
+              SyscallFailsWithErrno(EISDIR));
+}
+
+TEST(CreateTeast, CreatDirWithOTruncAndReadOnly) {
+  std::string dirpath = JoinPath(GetAbsoluteTestTmpdir(), "truncd");
+  ASSERT_THAT(mkdir(dirpath.c_str(), 0777), SyscallSucceeds());
+  ASSERT_THAT(open(dirpath.c_str(), O_CREAT | O_TRUNC | O_RDONLY, 0666),
+              SyscallFailsWithErrno(EISDIR));
+}
+
+TEST(CreateTeast, CreatFileWithOTruncAndReadOnly) {
+  std::string dirpath = JoinPath(GetAbsoluteTestTmpdir(), "truncfile");
+  int dirfd;
+  ASSERT_THAT(dirfd = open(dirpath.c_str(), O_RDWR | O_CREAT, 0666),
+              SyscallSucceeds());
+  ASSERT_THAT(open(dirpath.c_str(), O_CREAT | O_TRUNC | O_RDONLY, 0666),
+              SyscallSucceeds());
+  ASSERT_THAT(close(dirfd), SyscallSucceeds());
+}
+
 TEST(CreateTest, CreateFailsOnUnpermittedDir) {
   // Make sure we don't have CAP_DAC_OVERRIDE, since that allows the user to
   // always override directory permissions.
diff --git a/test/syscalls/linux/pty.cc b/test/syscalls/linux/pty.cc
index 99a0df235..dafe64d20 100644
--- a/test/syscalls/linux/pty.cc
+++ b/test/syscalls/linux/pty.cc
@@ -70,6 +70,8 @@ constexpr absl::Duration kTimeout = absl::Seconds(20);
 // The maximum line size in bytes returned per read from a pty file.
 constexpr int kMaxLineSize = 4096;
 
+constexpr char kMasterPath[] = "/dev/ptmx";
+
 // glibc defines its own, different, version of struct termios. We care about
 // what the kernel does, not glibc.
 #define KERNEL_NCCS 19
@@ -376,9 +378,25 @@ PosixErrorOr<size_t> PollAndReadFd(int fd, void* buf, size_t count,
   return PosixError(ETIMEDOUT, "Poll timed out");
 }
 
+TEST(PtyTrunc, Truncate) {
+  // Opening PTYs with O_TRUNC shouldn't cause an error, but calls to
+  // (f)truncate should.
+  FileDescriptor master =
+      ASSERT_NO_ERRNO_AND_VALUE(Open(kMasterPath, O_RDWR | O_TRUNC));
+  int n = ASSERT_NO_ERRNO_AND_VALUE(SlaveID(master));
+  std::string spath = absl::StrCat("/dev/pts/", n);
+  FileDescriptor slave =
+      ASSERT_NO_ERRNO_AND_VALUE(Open(spath, O_RDWR | O_NONBLOCK | O_TRUNC));
+
+  EXPECT_THAT(truncate(kMasterPath, 0), SyscallFailsWithErrno(EINVAL));
+  EXPECT_THAT(truncate(spath.c_str(), 0), SyscallFailsWithErrno(EINVAL));
+  EXPECT_THAT(ftruncate(master.get(), 0), SyscallFailsWithErrno(EINVAL));
+  EXPECT_THAT(ftruncate(slave.get(), 0), SyscallFailsWithErrno(EINVAL));
+}
+
 TEST(BasicPtyTest, StatUnopenedMaster) {
   struct stat s;
-  ASSERT_THAT(stat("/dev/ptmx", &s), SyscallSucceeds());
+  ASSERT_THAT(stat(kMasterPath, &s), SyscallSucceeds());
 
   EXPECT_EQ(s.st_rdev, makedev(TTYAUX_MAJOR, kPtmxMinor));
   EXPECT_EQ(s.st_size, 0);
diff --git a/test/util/pty_util.cc b/test/util/pty_util.cc
index c0fd9a095..c01f916aa 100644
--- a/test/util/pty_util.cc
+++ b/test/util/pty_util.cc
@@ -24,6 +24,14 @@ namespace gvisor {
 namespace testing {
 
 PosixErrorOr<FileDescriptor> OpenSlave(const FileDescriptor& master) {
+  PosixErrorOr<int> n = SlaveID(master);
+  if (!n.ok()) {
+    return PosixErrorOr<FileDescriptor>(n.error());
+  }
+  return Open(absl::StrCat("/dev/pts/", n.ValueOrDie()), O_RDWR | O_NONBLOCK);
+}
+
+PosixErrorOr<int> SlaveID(const FileDescriptor& master) {
   // Get pty index.
   int n;
   int ret = ioctl(master.get(), TIOCGPTN, &n);
@@ -38,7 +46,7 @@ PosixErrorOr<FileDescriptor> OpenSlave(const FileDescriptor& master) {
     return PosixError(errno, "ioctl(TIOSPTLCK) failed");
   }
 
-  return Open(absl::StrCat("/dev/pts/", n), O_RDWR | O_NONBLOCK);
+  return n;
 }
 
 }  // namespace testing
diff --git a/test/util/pty_util.h b/test/util/pty_util.h
index 367b14f15..0722da379 100644
--- a/test/util/pty_util.h
+++ b/test/util/pty_util.h
@@ -24,6 +24,9 @@ namespace testing {
 // Opens the slave end of the passed master as R/W and nonblocking.
 PosixErrorOr<FileDescriptor> OpenSlave(const FileDescriptor& master);
 
+// Get the number of the slave end of the master.
+PosixErrorOr<int> SlaveID(const FileDescriptor& master);
+
 }  // namespace testing
 }  // namespace gvisor