[vfs2][gofer] Fix file creation flags sent to gofer.

Fixes php runtime test ext/standard/tests/file/readfile_basic.phpt
Fixes #3516

fsgofers only want the access mode in the OpenFlags passed to Create(). If more
flags are supplied (like O_APPEND in this case), read/write from that fd will
fail with EBADF. See runsc/fsgofer/fsgofer.go:WriteAt()
VFS2 was providing more than just access modes. So filtering the flags using
p9.OpenFlagsModeMask == linux.O_ACCMODE fixes the issue.

Gofer in VFS1 also only extracts the access mode flags while making the create
RPC. See pkg/sentry/fs/gofer/path.go:Create()

Even in VFS2, when we open a handle, we extract out only the access mode flags
+ O_TRUNC.
See third_party/gvisor/pkg/sentry/fsimpl/gofer/handle.go:openHandle()

Added a test for this.

PiperOrigin-RevId: 326574829

1 files changed, 20 insertions, 0 deletions

diff --git a/test/syscalls/linux/open.cc b/test/syscalls/linux/open.cc
index c7147c20b..8f0c9cb49 100644
--- a/test/syscalls/linux/open.cc
+++ b/test/syscalls/linux/open.cc
@@ -147,6 +147,26 @@ TEST_F(OpenTest, WriteOnly) {
   EXPECT_THAT(write(wo_file.get(), &buf, 1), SyscallSucceedsWithValue(1));
 }
 
+TEST_F(OpenTest, CreateWithAppend) {
+  std::string data = "text";
+  std::string new_file = NewTempAbsPath();
+  const FileDescriptor file = ASSERT_NO_ERRNO_AND_VALUE(
+      Open(new_file, O_WRONLY | O_APPEND | O_CREAT, 0666));
+  EXPECT_THAT(write(file.get(), data.c_str(), data.size()),
+              SyscallSucceedsWithValue(data.size()));
+  EXPECT_THAT(lseek(file.get(), 0, SEEK_SET), SyscallSucceeds());
+  EXPECT_THAT(write(file.get(), data.c_str(), data.size()),
+              SyscallSucceedsWithValue(data.size()));
+
+  // Check that the size of the file is correct and that the offset has been
+  // incremented to that size.
+  struct stat s0;
+  EXPECT_THAT(fstat(file.get(), &s0), SyscallSucceeds());
+  EXPECT_EQ(s0.st_size, 2 * data.size());
+  EXPECT_THAT(lseek(file.get(), 0, SEEK_CUR),
+              SyscallSucceedsWithValue(2 * data.size()));
+}
+
 TEST_F(OpenTest, ReadWrite) {
   char buf;
   const FileDescriptor rw_file =