Add support for flexible filename limits for tmpfs.

PiperOrigin-RevId: 413038601

pkg/sentry/fsimpl/gofer/filesystem.go

@@ -117,9 +117,9 @@ func (fs *filesystem) Sync(ctx context.Context) error {
 	return retErr
 }
 
-// maxFilenameLen is the maximum length of a filename. This is dictated by 9P's
+// MaxFilenameLen is the maximum length of a filename. This is dictated by 9P's
 // encoding of strings, which uses 2 bytes for the length prefix.
-const maxFilenameLen = (1 << 16) - 1
+const MaxFilenameLen = (1 << 16) - 1
 
 // dentrySlicePool is a pool of *[]*dentry used to store dentries for which
 // dentry.checkCachingLocked() must be called. The pool holds pointers to
@@ -275,7 +275,7 @@ func (fs *filesystem) getChildAndWalkPathLocked(ctx context.Context, parent *den
 	// Note that pit is a copy of the iterator that does not affect rp.
 	pit := rp.Pit()
 	first := pit.String()
-	if len(first) > maxFilenameLen {
+	if len(first) > MaxFilenameLen {
 		return nil, linuxerr.ENAMETOOLONG
 	}
 	if child, ok := parent.children[first]; ok || parent.isSynthetic() {
@@ -368,7 +368,7 @@ func (fs *filesystem) getChildAndWalkPathLocked(ctx context.Context, parent *den
 // * name is not "." or "..".
 // * parent and the dentry at name have been revalidated.
 func (fs *filesystem) getChildLocked(ctx context.Context, parent *dentry, name string, ds **[]*dentry) (*dentry, error) {
-	if len(name) > maxFilenameLen {
+	if len(name) > MaxFilenameLen {
 		return nil, linuxerr.ENAMETOOLONG
 	}
 	if child, ok := parent.children[name]; ok || parent.isSynthetic() {
@@ -511,7 +511,7 @@ func (fs *filesystem) doCreateAt(ctx context.Context, rp *vfs.ResolvingPath, dir
 	parent.dirMu.Lock()
 	defer parent.dirMu.Unlock()
 
-	if len(name) > maxFilenameLen {
+	if len(name) > MaxFilenameLen {
 		return linuxerr.ENAMETOOLONG
 	}
 	// Check for existence only if caching information is available. Otherwise,
@@ -1696,8 +1696,8 @@ 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 == 0 || statFS.NameLength > maxFilenameLen {
-			statFS.NameLength = maxFilenameLen
+		if statFS.NameLength == 0 || statFS.NameLength > MaxFilenameLen {
+			statFS.NameLength = MaxFilenameLen
 		}
 		return linux.Statfs{
 			// This is primarily for distinguishing a gofer file system in
@@ -1719,8 +1719,8 @@ func (fs *filesystem) StatFSAt(ctx context.Context, rp *vfs.ResolvingPath) (linu
 		return linux.Statfs{}, err
 	}
 	nameLen := uint64(fsstat.NameLength)
-	if nameLen == 0 || nameLen > maxFilenameLen {
-		nameLen = maxFilenameLen
+	if nameLen == 0 || nameLen > MaxFilenameLen {
+		nameLen = MaxFilenameLen
 	}
 	return linux.Statfs{
 		// This is primarily for distinguishing a gofer file system in

pkg/sentry/fsimpl/tmpfs/filesystem.go

@@ -69,7 +69,7 @@ afterSymlink:
 		rp.Advance()
 		return d.parent, nil
 	}
-	if len(name) > linux.NAME_MAX {
+	if len(name) > d.inode.fs.maxFilenameLen {
 		return nil, linuxerr.ENAMETOOLONG
 	}
 	child, ok := dir.childMap[name]
@@ -163,7 +163,7 @@ func (fs *filesystem) doCreateAt(ctx context.Context, rp *vfs.ResolvingPath, dir
 	if name == "." || name == ".." {
 		return linuxerr.EEXIST
 	}
-	if len(name) > linux.NAME_MAX {
+	if len(name) > fs.maxFilenameLen {
 		return linuxerr.ENAMETOOLONG
 	}
 	if _, ok := parentDir.childMap[name]; ok {
@@ -371,7 +371,7 @@ afterTrailingSymlink:
 	if name == "." || name == ".." {
 		return nil, linuxerr.EISDIR
 	}
-	if len(name) > linux.NAME_MAX {
+	if len(name) > fs.maxFilenameLen {
 		return nil, linuxerr.ENAMETOOLONG
 	}
 	// Determine whether or not we need to create a file.

pkg/sentry/fsimpl/tmpfs/tmpfs.go

@@ -85,6 +85,8 @@ type filesystem struct {
 	nextInoMinusOne uint64 // accessed using atomic memory operations
 
 	root *dentry
+
+	maxFilenameLen int
 }
 
 // Name implements vfs.FilesystemType.Name.
@@ -115,6 +117,9 @@ type FilesystemOpts struct {
 	// Usage is the memory accounting category under which pages backing files in
 	// the filesystem are accounted.
 	Usage *usage.MemoryKind
+
+	// MaxFilenameLen is the maximum filename length allowed by the tmpfs.
+	MaxFilenameLen int
 }
 
 // GetFilesystem implements vfs.FilesystemType.GetFilesystem.
@@ -126,8 +131,8 @@ func (fstype FilesystemType) GetFilesystem(ctx context.Context, vfsObj *vfs.Virt
 
 	rootFileType := uint16(linux.S_IFDIR)
 	newFSType := vfs.FilesystemType(&fstype)
-	tmpfsOpts, ok := opts.InternalData.(FilesystemOpts)
-	if ok {
+	tmpfsOpts, tmpfsOptsOk := opts.InternalData.(FilesystemOpts)
+	if tmpfsOptsOk {
 		if tmpfsOpts.RootFileType != 0 {
 			rootFileType = tmpfsOpts.RootFileType
 		}
@@ -198,13 +203,17 @@ func (fstype FilesystemType) GetFilesystem(ctx context.Context, vfsObj *vfs.Virt
 		memUsage = *tmpfsOpts.Usage
 	}
 	fs := filesystem{
-		mfp:      mfp,
-		clock:    clock,
-		devMinor: devMinor,
-		mopts:    opts.Data,
-		usage:    memUsage,
+		mfp:            mfp,
+		clock:          clock,
+		devMinor:       devMinor,
+		mopts:          opts.Data,
+		usage:          memUsage,
+		maxFilenameLen: linux.NAME_MAX,
 	}
 	fs.vfsfs.Init(vfsObj, newFSType, &fs)
+	if tmpfsOptsOk && tmpfsOpts.MaxFilenameLen > 0 {
+		fs.maxFilenameLen = tmpfsOpts.MaxFilenameLen
+	}
 
 	var root *dentry
 	switch rootFileType {