Update CHANGELOG.md

CHANGELOG.md

@@ -1,5 +1,13 @@
 # Changelog
 
+## v1.7.4
+### Fixed
+* CVE-2023-25168
+
+## v1.7.3
+### Fixed
+* CVE-2023-25152
+
 ## v1.7.2
 ### Fixed
 * The S3 backup driver now supports Cloudflare R2

server/filesystem/filesystem.go

@@ -159,7 +159,7 @@ func (fs *Filesystem) Writefile(p string, r io.Reader) error {
 	// Adjust the disk usage to account for the old size and the new size of the file.
 	fs.addDisk(sz - currentSize)
 
-	return fs.Chown(cleaned)
+	return fs.unsafeChown(cleaned)
 }
 
 // Creates a new directory (name) at a specified path (p) for the server.
@@ -217,7 +217,12 @@ func (fs *Filesystem) Chown(path string) error {
 	if err != nil {
 		return err
 	}
+	return fs.unsafeChown(cleaned)
+}
 
+// unsafeChown chowns the given path, without checking if the path is safe. This should only be used
+// when the path has already been checked.
+func (fs *Filesystem) unsafeChown(path string) error {
 	if fs.isTest {
 		return nil
 	}
@@ -226,19 +231,19 @@ func (fs *Filesystem) Chown(path string) error {
 	gid := config.Get().System.User.Gid
 
 	// Start by just chowning the initial path that we received.
-	if err := os.Chown(cleaned, uid, gid); err != nil {
+	if err := os.Chown(path, uid, gid); err != nil {
 		return errors.Wrap(err, "server/filesystem: chown: failed to chown path")
 	}
 
 	// If this is not a directory we can now return from the function, there is nothing
 	// left that we need to do.
-	if st, err := os.Stat(cleaned); err != nil || !st.IsDir() {
+	if st, err := os.Stat(path); err != nil || !st.IsDir() {
 		return nil
 	}
 
 	// If this was a directory, begin walking over its contents recursively and ensure that all
 	// of the subfiles and directories get their permissions updated as well.
-	err = godirwalk.Walk(cleaned, &godirwalk.Options{
+	err := godirwalk.Walk(path, &godirwalk.Options{
 		Unsorted: true,
 		Callback: func(p string, e *godirwalk.Dirent) error {
 			// Do not attempt to chown a symlink. Go's os.Chown function will affect the symlink
@@ -255,7 +260,6 @@ func (fs *Filesystem) Chown(path string) error {
 			return os.Chown(p, uid, gid)
 		},
 	})
-
 	return errors.Wrap(err, "server/filesystem: chown: failed to chown during walk function")
 }
 
@@ -377,10 +381,9 @@ func (fs *Filesystem) TruncateRootDirectory() error {
 // Delete removes a file or folder from the system. Prevents the user from
 // accidentally (or maliciously) removing their root server data directory.
 func (fs *Filesystem) Delete(p string) error {
-	wg := sync.WaitGroup{}
 	// This is one of the few (only?) places in the codebase where we're explicitly not using
 	// the SafePath functionality when working with user provided input. If we did, you would
-	// not be able to delete a file that is a symlink pointing to a location outside of the data
+	// not be able to delete a file that is a symlink pointing to a location outside the data
 	// directory.
 	//
 	// We also want to avoid resolving a symlink that points _within_ the data directory and thus
@@ -397,25 +400,65 @@ func (fs *Filesystem) Delete(p string) error {
 		return errors.New("cannot delete root server directory")
 	}
 
-	if st, err := os.Lstat(resolved); err != nil {
+	st, err := os.Lstat(resolved)
+	if err != nil {
 		if !os.IsNotExist(err) {
 			fs.error(err).Warn("error while attempting to stat file before deletion")
+			return err
 		}
-	} else {
-		if !st.IsDir() {
-			fs.addDisk(-st.Size())
-		} else {
-			wg.Add(1)
-			go func(wg *sync.WaitGroup, st os.FileInfo, resolved string) {
-				defer wg.Done()
-				if s, err := fs.DirectorySize(resolved); err == nil {
-					fs.addDisk(-s)
+
+		// The following logic is used to handle a case where a user attempts to
+		// delete a file that does not exist through a directory symlink.
+		// We don't want to reveal that the file does not exist, so we validate
+		// the path of the symlink and return a bad path error if it is invalid.
+
+		// The requested file or directory doesn't exist, so at this point we
+		// need to iterate up the path chain until we hit a directory that
+		// _does_ exist and can be validated.
+		parts := strings.Split(filepath.Dir(resolved), "/")
+
+		// Range over all the path parts and form directory paths from the end
+		// moving up until we have a valid resolution, or we run out of paths to
+		// try.
+		for k := range parts {
+			try := strings.Join(parts[:(len(parts)-k)], "/")
+			if !fs.unsafeIsInDataDirectory(try) {
+				break
 			}
-			}(&wg, st, resolved)
+
+			t, err := filepath.EvalSymlinks(try)
+			if err == nil {
+				if !fs.unsafeIsInDataDirectory(t) {
+					return NewBadPathResolution(p, t)
+				}
+				break
 			}
 		}
 
-	wg.Wait()
+		// Always return early if the file does not exist.
+		return nil
+	}
+
+	// If the file is not a symlink, we need to check that it is not within a
+	// symlinked directory that points outside the data directory.
+	if st.Mode()&os.ModeSymlink == 0 {
+		ep, err := filepath.EvalSymlinks(resolved)
+		if err != nil {
+			if !os.IsNotExist(err) {
+				return err
+			}
+		} else if !fs.unsafeIsInDataDirectory(ep) {
+			return NewBadPathResolution(p, ep)
+		}
+	}
+
+	if st.IsDir() {
+		if s, err := fs.DirectorySize(resolved); err == nil {
+			fs.addDisk(-s)
+		}
+	} else {
+		fs.addDisk(-st.Size())
+	}
 
 	return os.RemoveAll(resolved)
 }

server/filesystem/filesystem_test.go

@@ -508,6 +508,80 @@ func TestFilesystem_Delete(t *testing.T) {
 			}
 		})
 
+		g.It("deletes a symlink but not it's target within the root directory", func() {
+			// Symlink to a file inside the root directory.
+			err := os.Symlink(filepath.Join(rfs.root, "server/source.txt"), filepath.Join(rfs.root, "server/symlink.txt"))
+			g.Assert(err).IsNil()
+
+			// Delete the symlink itself.
+			err = fs.Delete("symlink.txt")
+			g.Assert(err).IsNil()
+
+			// Ensure the symlink was deleted.
+			_, err = os.Lstat(filepath.Join(rfs.root, "server/symlink.txt"))
+			g.Assert(err).IsNotNil()
+
+			// Ensure the symlink target still exists.
+			_, err = os.Lstat(filepath.Join(rfs.root, "server/source.txt"))
+			g.Assert(err).IsNil()
+		})
+
+		g.It("does not delete files symlinked outside of the root directory", func() {
+			// Create a file outside the root directory.
+			err := rfs.CreateServerFileFromString("/../source.txt", "test content")
+			g.Assert(err).IsNil()
+
+			// Create a symlink to the file outside the root directory.
+			err = os.Symlink(filepath.Join(rfs.root, "source.txt"), filepath.Join(rfs.root, "/server/symlink.txt"))
+			g.Assert(err).IsNil()
+
+			// Delete the symlink. (This should pass as we will delete the symlink itself, not it's target)
+			err = fs.Delete("symlink.txt")
+			g.Assert(err).IsNil()
+
+			// Ensure the file outside the root directory still exists.
+			_, err = os.Lstat(filepath.Join(rfs.root, "source.txt"))
+			g.Assert(err).IsNil()
+		})
+
+		g.It("does not delete files symlinked through a directory outside of the root directory", func() {
+			// Create a directory outside the root directory.
+			err := os.Mkdir(filepath.Join(rfs.root, "foo"), 0o755)
+			g.Assert(err).IsNil()
+
+			// Create a file inside the directory that is outside the root.
+			err = rfs.CreateServerFileFromString("/../foo/source.txt", "test content")
+			g.Assert(err).IsNil()
+
+			// Symlink the directory that is outside the root to a file inside the root.
+			err = os.Symlink(filepath.Join(rfs.root, "foo"), filepath.Join(rfs.root, "server/symlink"))
+			g.Assert(err).IsNil()
+
+			// Delete a file inside the symlinked directory.
+			err = fs.Delete("symlink/source.txt")
+			g.Assert(err).IsNotNil()
+			g.Assert(IsErrorCode(err, ErrCodePathResolution)).IsTrue()
+
+			// Ensure the file outside the root directory still exists.
+			_, err = os.Lstat(filepath.Join(rfs.root, "foo/source.txt"))
+			g.Assert(err).IsNil()
+		})
+
+		g.It("returns an error when trying to delete a non-existent file symlinked through a directory outside of the root directory", func() {
+			// Create a directory outside the root directory.
+			err := os.Mkdir(filepath.Join(rfs.root, "foo2"), 0o755)
+			g.Assert(err).IsNil()
+
+			// Symlink the directory that is outside the root to a file inside the root.
+			err = os.Symlink(filepath.Join(rfs.root, "foo2"), filepath.Join(rfs.root, "server/symlink"))
+			g.Assert(err).IsNil()
+
+			// Delete a file inside the symlinked directory.
+			err = fs.Delete("symlink/source.txt")
+			g.Assert(err).IsNotNil()
+			g.Assert(IsErrorCode(err, ErrCodePathResolution)).IsTrue()
+		})
+
 		g.AfterEach(func() {
 			rfs.reset()
 

server/filesystem/path.go

@@ -2,6 +2,7 @@ package filesystem
 
 import (
 	"context"
+	iofs "io/fs"
 	"os"
 	"path/filepath"
 	"strings"
@@ -33,8 +34,6 @@ func (fs *Filesystem) IsIgnored(paths ...string) error {
 // This logic is actually copied over from the SFTP server code. Ideally that eventually
 // either gets ported into this application, or is able to make use of this package.
 func (fs *Filesystem) SafePath(p string) (string, error) {
-	var nonExistentPathResolution string
-
 	// Start with a cleaned up path before checking the more complex bits.
 	r := fs.unsafeFilePath(p)
 
@@ -44,47 +43,24 @@ func (fs *Filesystem) SafePath(p string) (string, error) {
 	if err != nil && !os.IsNotExist(err) {
 		return "", errors.Wrap(err, "server/filesystem: failed to evaluate symlink")
 	} else if os.IsNotExist(err) {
-		// The requested directory doesn't exist, so at this point we need to iterate up the
-		// path chain until we hit a directory that _does_ exist and can be validated.
-		parts := strings.Split(filepath.Dir(r), "/")
-
-		var try string
-		// Range over all of the path parts and form directory pathings from the end
-		// moving up until we have a valid resolution or we run out of paths to try.
-		for k := range parts {
-			try = strings.Join(parts[:(len(parts)-k)], "/")
-
-			if !fs.unsafeIsInDataDirectory(try) {
-				break
+		// The target of one of the symlinks (EvalSymlinks is recursive) does not exist.
+		// So we get what target path does not exist and check if it's within the data
+		// directory. If it is, we return the original path, otherwise we return an error.
+		pErr, ok := err.(*iofs.PathError)
+		if !ok {
+			return "", errors.Wrap(err, "server/filesystem: failed to evaluate symlink")
 		}
-
-			t, err := filepath.EvalSymlinks(try)
-			if err == nil {
-				nonExistentPathResolution = t
-				break
-			}
-		}
-	}
-
-	// If the new path doesn't start with their root directory there is clearly an escape
-	// attempt going on, and we should NOT resolve this path for them.
-	if nonExistentPathResolution != "" {
-		if !fs.unsafeIsInDataDirectory(nonExistentPathResolution) {
-			return "", NewBadPathResolution(p, nonExistentPathResolution)
-		}
-
-		// If the nonExistentPathResolution variable is not empty then the initial path requested
-		// did not exist and we looped through the pathway until we found a match. At this point
-		// we've confirmed the first matched pathway exists in the root server directory, so we
-		// can go ahead and just return the path that was requested initially.
-		return r, nil
+		ep = pErr.Path
 	}
 
 	// If the requested directory from EvalSymlinks begins with the server root directory go
 	// ahead and return it. If not we'll return an error which will block any further action
 	// on the file.
 	if fs.unsafeIsInDataDirectory(ep) {
-		return ep, nil
+		// Returning the original path here instead of the resolved path ensures that
+		// whatever the user is trying to do will work as expected. If we returned the
+		// resolved path, the user would be unable to know that it is in fact a symlink.
+		return r, nil
 	}
 
 	return "", NewBadPathResolution(p, r)

server/filesystem/path_test.go

@@ -115,6 +115,14 @@ func TestFilesystem_Blocks_Symlinks(t *testing.T) {
 		panic(err)
 	}
 
+	if err := os.Symlink(filepath.Join(rfs.root, "malicious_does_not_exist.txt"), filepath.Join(rfs.root, "/server/symlinked_does_not_exist.txt")); err != nil {
+		panic(err)
+	}
+
+	if err := os.Symlink(filepath.Join(rfs.root, "/server/symlinked_does_not_exist.txt"), filepath.Join(rfs.root, "/server/symlinked_does_not_exist2.txt")); err != nil {
+		panic(err)
+	}
+
 	if err := os.Symlink(filepath.Join(rfs.root, "/malicious_dir"), filepath.Join(rfs.root, "/server/external_dir")); err != nil {
 		panic(err)
 	}
@@ -128,6 +136,22 @@ func TestFilesystem_Blocks_Symlinks(t *testing.T) {
 			g.Assert(IsErrorCode(err, ErrCodePathResolution)).IsTrue()
 		})
 
+		g.It("cannot write to a non-existent file symlinked outside the root", func() {
+			r := bytes.NewReader([]byte("testing what the fuck"))
+
+			err := fs.Writefile("symlinked_does_not_exist.txt", r)
+			g.Assert(err).IsNotNil()
+			g.Assert(IsErrorCode(err, ErrCodePathResolution)).IsTrue()
+		})
+
+		g.It("cannot write to chained symlinks with target that does not exist outside the root", func() {
+			r := bytes.NewReader([]byte("testing what the fuck"))
+
+			err := fs.Writefile("symlinked_does_not_exist2.txt", r)
+			g.Assert(err).IsNotNil()
+			g.Assert(IsErrorCode(err, ErrCodePathResolution)).IsTrue()
+		})
+
 		g.It("cannot write a file to a directory symlinked outside the root", func() {
 			r := bytes.NewReader([]byte("testing"))