Don't enforce NAME_MAX in fs.Dirent.walk().

Maximum filename length is filesystem-dependent, and obtained via
statfs::f_namelen. This limit is usually 255 bytes (NAME_MAX), but not
always. For example, VFAT supports filenames of up to 255... UCS-2
characters, which Linux conservatively takes to mean UTF-8-encoded
bytes: fs/fat/inode.c:fat_statfs(), FAT_LFN_LEN * NLS_MAX_CHARSET_SIZE.
As a result, Linux's VFS does not enforce NAME_MAX:

$ rg --maxdepth=1 '\WNAME_MAX\W' fs/ include/linux/
fs/libfs.c
38:     buf->f_namelen = NAME_MAX;
64:     if (dentry->d_name.len > NAME_MAX)

include/linux/relay.h
74:     char base_filename[NAME_MAX];   /* saved base filename */

include/linux/fscrypt.h
149: * filenames up to NAME_MAX bytes, since base64 encoding expands the length.

include/linux/exportfs.h
176: *    understanding that it is already pointing to a a %NAME_MAX+1 sized

Remove this check from core VFS, and add it to ramfs (and by extension
tmpfs), where it is actually applicable:
mm/shmem.c:shmem_dir_inode_operations.lookup == simple_lookup *does*
enforce NAME_MAX.

PiperOrigin-RevId: 245324748
Change-Id: I17567c4324bfd60e31746a5270096e75db963fac

1 files changed, 23 insertions, 0 deletions

diff --git a/pkg/sentry/fs/ramfs/dir.go b/pkg/sentry/fs/ramfs/dir.go
index 011cf3a16..159fd2981 100644
--- a/pkg/sentry/fs/ramfs/dir.go
+++ b/pkg/sentry/fs/ramfs/dir.go
@@ -192,6 +192,10 @@ func (d *Dir) removeChildLocked(ctx context.Context, name string) (*fs.Inode, er
 
 // Remove removes the named non-directory.
 func (d *Dir) Remove(ctx context.Context, _ *fs.Inode, name string) error {
+	if len(name) > linux.NAME_MAX {
+		return syserror.ENAMETOOLONG
+	}
+
 	d.mu.Lock()
 	defer d.mu.Unlock()
 	inode, err := d.removeChildLocked(ctx, name)
@@ -206,6 +210,10 @@ func (d *Dir) Remove(ctx context.Context, _ *fs.Inode, name string) error {
 
 // RemoveDirectory removes the named directory.
 func (d *Dir) RemoveDirectory(ctx context.Context, _ *fs.Inode, name string) error {
+	if len(name) > linux.NAME_MAX {
+		return syserror.ENAMETOOLONG
+	}
+
 	d.mu.Lock()
 	defer d.mu.Unlock()
 
@@ -234,6 +242,10 @@ func (d *Dir) RemoveDirectory(ctx context.Context, _ *fs.Inode, name string) err
 
 // Lookup loads an inode at p into a Dirent.
 func (d *Dir) Lookup(ctx context.Context, _ *fs.Inode, p string) (*fs.Dirent, error) {
+	if len(p) > linux.NAME_MAX {
+		return nil, syserror.ENAMETOOLONG
+	}
+
 	d.mu.Lock()
 	defer d.mu.Unlock()
 
@@ -265,6 +277,10 @@ func (d *Dir) walkLocked(ctx context.Context, p string) (*fs.Inode, error) {
 // createInodeOperationsCommon creates a new child node at this dir by calling
 // makeInodeOperations. It is the common logic for creating a new child.
 func (d *Dir) createInodeOperationsCommon(ctx context.Context, name string, makeInodeOperations func() (*fs.Inode, error)) (*fs.Inode, error) {
+	if len(name) > linux.NAME_MAX {
+		return nil, syserror.ENAMETOOLONG
+	}
+
 	d.mu.Lock()
 	defer d.mu.Unlock()
 
@@ -314,6 +330,10 @@ func (d *Dir) CreateLink(ctx context.Context, dir *fs.Inode, oldname, newname st
 
 // CreateHardLink creates a new hard link.
 func (d *Dir) CreateHardLink(ctx context.Context, dir *fs.Inode, target *fs.Inode, name string) error {
+	if len(name) > linux.NAME_MAX {
+		return syserror.ENAMETOOLONG
+	}
+
 	d.mu.Lock()
 	defer d.mu.Unlock()
 
@@ -465,6 +485,9 @@ func Rename(ctx context.Context, oldParent fs.InodeOperations, oldName string, n
 	if !ok {
 		return syserror.EXDEV
 	}
+	if len(newName) > linux.NAME_MAX {
+		return syserror.ENAMETOOLONG
+	}
 
 	np.mu.Lock()
 	defer np.mu.Unlock()