Ensure statfs::f_namelen is set by VFS2 gofer statfs/fstatfs.

VFS1 discards the value of f_namelen returned by the filesystem and returns
NAME_MAX unconditionally instead, so it doesn't run into this. Also set
f_frsize for completeness.

PiperOrigin-RevId: 405579707

2 files changed, 13 insertions, 4 deletions

diff --git a/pkg/sentry/fsimpl/gofer/filesystem.go b/pkg/sentry/fsimpl/gofer/filesystem.go
index 23c8b8ce3..bf58a9def 100644
--- a/pkg/sentry/fsimpl/gofer/filesystem.go
+++ b/pkg/sentry/fsimpl/gofer/filesystem.go
@@ -1696,7 +1696,7 @@ func (fs *filesystem) StatFSAt(ctx context.Context, rp *vfs.ResolvingPath) (linu
 		if err := d.controlFDLisa.StatFSTo(ctx, &statFS); err != nil {
 			return linux.Statfs{}, err
 		}
-		if statFS.NameLength > maxFilenameLen {
+		if statFS.NameLength == 0 || statFS.NameLength > maxFilenameLen {
 			statFS.NameLength = maxFilenameLen
 		}
 		return linux.Statfs{
@@ -1705,6 +1705,7 @@ func (fs *filesystem) StatFSAt(ctx context.Context, rp *vfs.ResolvingPath) (linu
 			// something completely random, use a standard value.
 			Type:            linux.V9FS_MAGIC,
 			BlockSize:       statFS.BlockSize,
+			FragmentSize:    statFS.BlockSize,
 			Blocks:          statFS.Blocks,
 			BlocksFree:      statFS.BlocksFree,
 			BlocksAvailable: statFS.BlocksAvailable,
@@ -1718,7 +1719,7 @@ func (fs *filesystem) StatFSAt(ctx context.Context, rp *vfs.ResolvingPath) (linu
 		return linux.Statfs{}, err
 	}
 	nameLen := uint64(fsstat.NameLength)
-	if nameLen > maxFilenameLen {
+	if nameLen == 0 || nameLen > maxFilenameLen {
 		nameLen = maxFilenameLen
 	}
 	return linux.Statfs{
@@ -1727,6 +1728,7 @@ func (fs *filesystem) StatFSAt(ctx context.Context, rp *vfs.ResolvingPath) (linu
 		// something completely random, use a standard value.
 		Type:            linux.V9FS_MAGIC,
 		BlockSize:       int64(fsstat.BlockSize),
+		FragmentSize:    int64(fsstat.BlockSize),
 		Blocks:          fsstat.Blocks,
 		BlocksFree:      fsstat.BlocksFree,
 		BlocksAvailable: fsstat.BlocksAvailable,
diff --git a/test/syscalls/linux/statfs.cc b/test/syscalls/linux/statfs.cc
index d057cdc09..b447b5cce 100644
--- a/test/syscalls/linux/statfs.cc
+++ b/test/syscalls/linux/statfs.cc
@@ -34,17 +34,19 @@ TEST(StatfsTest, CannotStatBadPath) {
   EXPECT_THAT(statfs(temp_file.c_str(), &st), SyscallFailsWithErrno(ENOENT));
 }
 
-TEST(StatfsTest, InternalTmpfs) {
+TEST(StatfsTest, TempPath) {
   auto temp_file = ASSERT_NO_ERRNO_AND_VALUE(TempPath::CreateFile());
 
   struct statfs st;
   EXPECT_THAT(statfs(temp_file.path().c_str(), &st), SyscallSucceeds());
+  EXPECT_GT(st.f_namelen, 0);
 }
 
 TEST(StatfsTest, InternalDevShm) {
   struct statfs st;
   EXPECT_THAT(statfs("/dev/shm", &st), SyscallSucceeds());
 
+  EXPECT_GT(st.f_namelen, 0);
   // This assumes that /dev/shm is tmpfs.
   // Note: We could be an overlay on some configurations.
   EXPECT_TRUE(st.f_type == TMPFS_MAGIC || st.f_type == OVERLAYFS_SUPER_MAGIC);
@@ -55,13 +57,14 @@ TEST(FstatfsTest, CannotStatBadFd) {
   EXPECT_THAT(fstatfs(-1, &st), SyscallFailsWithErrno(EBADF));
 }
 
-TEST(FstatfsTest, InternalTmpfs) {
+TEST(FstatfsTest, TempPath) {
   auto temp_file = ASSERT_NO_ERRNO_AND_VALUE(TempPath::CreateFile());
   const FileDescriptor fd =
       ASSERT_NO_ERRNO_AND_VALUE(Open(temp_file.path(), O_RDONLY));
 
   struct statfs st;
   EXPECT_THAT(fstatfs(fd.get(), &st), SyscallSucceeds());
+  EXPECT_GT(st.f_namelen, 0);
 }
 
 TEST(FstatfsTest, CanStatFileWithOpath) {
@@ -81,6 +84,10 @@ TEST(FstatfsTest, InternalDevShm) {
 
   struct statfs st;
   EXPECT_THAT(fstatfs(fd.get(), &st), SyscallSucceeds());
+  EXPECT_GT(st.f_namelen, 0);
+  // This assumes that /dev/shm is tmpfs.
+  // Note: We could be an overlay on some configurations.
+  EXPECT_TRUE(st.f_type == TMPFS_MAGIC || st.f_type == OVERLAYFS_SUPER_MAGIC);
 }
 
 }  // namespace