fix: SFTP HomeDir path translation for user operations (#7611)

* fix: SFTP HomeDir path translation for user operations

When users have a non-root HomeDir (e.g., '/sftp/user'), their SFTP
operations should be relative to that directory. Previously, when a
user uploaded to '/' via SFTP, the path was not translated to their
home directory, causing 'permission denied for / for permission write'.

This fix adds a toAbsolutePath() method that implements chroot-like
behavior where the user's HomeDir becomes their root. All file and
directory operations now translate paths through this method.

Example: User with HomeDir='/sftp/user' uploading to '/' now correctly
maps to '/sftp/user'.

Fixes: https://github.com/seaweedfs/seaweedfs/issues/7470

* test: add SFTP integration tests

Add comprehensive integration tests for the SFTP server including:
- HomeDir path translation tests (verifies fix for issue #7470)
- Basic file upload/download operations
- Directory operations (mkdir, rmdir, list)
- Large file handling (1MB test)
- File rename operations
- Stat/Lstat operations
- Path edge cases (trailing slashes, .., unicode filenames)
- Admin root access verification

The test framework starts a complete SeaweedFS cluster with:
- Master server
- Volume server
- Filer server
- SFTP server with test user credentials

Test users are configured in testdata/userstore.json:
- admin: HomeDir=/ with full access
- testuser: HomeDir=/sftp/testuser with access to home
- readonly: HomeDir=/public with read-only access

* fix: correct SFTP HomeDir path translation and add CI

Fix path.Join issue where paths starting with '/' weren't joined correctly.
path.Join('/sftp/user', '/file') returns '/file' instead of '/sftp/user/file'.
Now we strip the leading '/' before joining.

Test improvements:
- Update go.mod to Go 1.24
- Fix weed binary discovery to prefer local build over PATH
- Add stabilization delay after service startup
- All 8 SFTP integration tests pass locally

Add GitHub Actions workflow for SFTP tests:
- Runs on push/PR affecting sftpd code or tests
- Tests HomeDir path translation, file ops, directory ops
- Covers issue #7470 fix verification

* security: update golang.org/x/crypto to v0.45.0

Addresses security vulnerability in golang.org/x/crypto < 0.45.0

* security: use proper SSH host key verification in tests

Replace ssh.InsecureIgnoreHostKey() with ssh.FixedHostKey() that
verifies the server's host key matches the known test key we generated.
This addresses CodeQL warning go/insecure-hostkeycallback.

Also updates go.mod to specify go 1.24.0 explicitly.

* security: fix path traversal vulnerability in SFTP toAbsolutePath

The previous implementation had a critical security vulnerability:
- Path traversal via '../..' could escape the HomeDir chroot jail
- Absolute paths were not correctly prefixed with HomeDir

The fix:
1. Concatenate HomeDir with userPath directly, then clean
2. Add security check to ensure final path stays within HomeDir
3. If traversal detected, safely return HomeDir instead

Also adds path traversal prevention tests to verify the fix.

* fix: address PR review comments

1. Fix SkipCleanup check to use actual test config instead of default
   - Added skipCleanup field to SftpTestFramework struct
   - Store config.SkipCleanup during Setup()
   - Use f.skipCleanup in Cleanup() instead of DefaultTestConfig()

2. Fix path prefix check false positive in mkdir
   - Changed from strings.HasPrefix(absPath, fs.user.HomeDir)
   - To: absPath == fs.user.HomeDir || strings.HasPrefix(absPath, fs.user.HomeDir+"/")
   - Prevents matching partial directory names (e.g., /sftp/username when HomeDir is /sftp/user)

* fix: check write permission on parent dir for mkdir

Aligns makeDir's permission check with newFileWriter for consistency.
To create a directory, a user needs write permission on the parent
directory, not mkdir permission on the new directory path.

* fix: refine SFTP path traversal logic and tests

1. Refine toAbsolutePath:
   - Use path.Join with strings.TrimPrefix for idiomatic path construction
   - Return explicit error on path traversal attempt instead of clamping
   - Updated all call sites to handle the error

2. Add Unit Tests:
   - Added sftp_server_test.go to verify toAbsolutePath logic
   - Covers normal paths, root path, and various traversal attempts

3. Update Integration Tests:
   - Updated PathTraversalPrevention test to reflect that standard SFTP clients
     sanitize paths before sending. The test now verifies successful containment
     within the jail rather than blocking (since the server receives a clean path).
   - The server-side blocking is verified by the new unit tests.

4. Makefile:
   - Removed -v from default test target

* fix: address PR comments on tests and makefile

1. Enhanced Unit Tests:
   - Added edge cases (empty path, multiple slashes, trailing slash) to sftp_server_test.go

2. Makefile Improvements:
   - Added 'all' target as default entry point

3. Code Clarity:
   - Added comment to mkdir permission check explaining defensive nature of HomeDir check

* fix: address PR review comments on permissions and tests

1. Security:
   - Added write permission check on target directory in renameEntry

2. Logging:
   - Changed dispatch log verbosity from V(0) to V(1)

3. Testing:
   - Updated Makefile .PHONY targets
   - Added unit test cases for empty/root HomeDir behavior in toAbsolutePath

* fix: set SFTP starting directory to virtual root

1. Critical Fix:
   - Changed sftp.WithStartDirectory from fs.user.HomeDir to '/'
   - Prevents double-prefixing when toAbsolutePath translates paths
   - Users now correctly start at their virtual root which maps to HomeDir

2. Test Improvements:
   - Use pointer for homeDir in tests for clearer nil vs empty distinction

* fix: clean HomeDir at config load time

Clean HomeDir path when loading users from JSON config.
This handles trailing slashes and other path anomalies at the source,
ensuring consistency throughout the codebase and avoiding repeated
cleaning on every toAbsolutePath call.

* test: strengthen assertions and add error checking in SFTP tests

1. Add error checking for cleanup operations in TestWalk
2. Strengthen cwd assertion to expect '/' explicitly in TestCurrentWorkingDirectory
3. Add error checking for cleanup in PathTraversalPrevention test

6 files changed, 191 insertions, 32 deletions

diff --git a/weed/sftpd/sftp_file_writer.go b/weed/sftpd/sftp_file_writer.go
index 0a662d021..fed60eec0 100644
--- a/weed/sftpd/sftp_file_writer.go
+++ b/weed/sftpd/sftp_file_writer.go
@@ -72,6 +72,7 @@ func (l listerat) ListAt(ls []os.FileInfo, offset int64) (int, error) {
 type SeaweedSftpFileWriter struct {
 	fs          SftpServer
 	req         *sftp.Request
+	absPath     string // Absolute path after HomeDir translation
 	mu          sync.Mutex
 	tmpFile     *os.File
 	permissions os.FileMode
@@ -105,6 +106,6 @@ func (w *SeaweedSftpFileWriter) Close() error {
 		return err
 	}
 
-	// Stream the file instead of loading it
-	return w.fs.putFile(w.req.Filepath, w.tmpFile, w.fs.user)
+	// Stream the file to the absolute path (after HomeDir translation)
+	return w.fs.putFile(w.absPath, w.tmpFile, w.fs.user)
 }
diff --git a/weed/sftpd/sftp_filer.go b/weed/sftpd/sftp_filer.go
index 9baaf41d7..eb196cc28 100644
--- a/weed/sftpd/sftp_filer.go
+++ b/weed/sftpd/sftp_filer.go
@@ -100,18 +100,26 @@ func (fs *SftpServer) withTimeoutContext(fn func(ctx context.Context) error) err
 // ==================== Command Dispatcher ====================
 
 func (fs *SftpServer) dispatchCmd(r *sftp.Request) error {
-	glog.V(0).Infof("Dispatch: %s %s", r.Method, r.Filepath)
+	absPath, err := fs.toAbsolutePath(r.Filepath)
+	if err != nil {
+		return err
+	}
+	glog.V(1).Infof("Dispatch: %s %s (absolute: %s)", r.Method, r.Filepath, absPath)
 	switch r.Method {
 	case "Remove":
-		return fs.removeEntry(r)
+		return fs.removeEntry(absPath)
 	case "Rename":
-		return fs.renameEntry(r)
+		absTarget, err := fs.toAbsolutePath(r.Target)
+		if err != nil {
+			return err
+		}
+		return fs.renameEntry(absPath, absTarget)
 	case "Mkdir":
-		return fs.makeDir(r)
+		return fs.makeDir(absPath)
 	case "Rmdir":
-		return fs.removeDir(r)
+		return fs.removeDir(absPath)
 	case "Setstat":
-		return fs.setFileStat(r)
+		return fs.setFileStatWithRequest(absPath, r)
 	default:
 		return fmt.Errorf("unsupported: %s", r.Method)
 	}
@@ -120,10 +128,14 @@ func (fs *SftpServer) dispatchCmd(r *sftp.Request) error {
 // ==================== File Operations ====================
 
 func (fs *SftpServer) readFile(r *sftp.Request) (io.ReaderAt, error) {
-	if err := fs.checkFilePermission(r.Filepath, "read"); err != nil {
+	absPath, err := fs.toAbsolutePath(r.Filepath)
+	if err != nil {
+		return nil, err
+	}
+	if err := fs.checkFilePermission(absPath, "read"); err != nil {
 		return nil, err
 	}
-	entry, err := fs.getEntry(r.Filepath)
+	entry, err := fs.getEntry(absPath)
 	if err != nil {
 		return nil, err
 	}
@@ -131,7 +143,11 @@ func (fs *SftpServer) readFile(r *sftp.Request) (io.ReaderAt, error) {
 }
 
 func (fs *SftpServer) newFileWriter(r *sftp.Request) (io.WriterAt, error) {
-	dir, _ := util.FullPath(r.Filepath).DirAndName()
+	absPath, err := fs.toAbsolutePath(r.Filepath)
+	if err != nil {
+		return nil, err
+	}
+	dir, _ := util.FullPath(absPath).DirAndName()
 	if err := fs.checkFilePermission(dir, "write"); err != nil {
 		glog.Errorf("Permission denied for %s", dir)
 		return nil, err
@@ -145,6 +161,7 @@ func (fs *SftpServer) newFileWriter(r *sftp.Request) (io.WriterAt, error) {
 	return &SeaweedSftpFileWriter{
 		fs:          *fs,
 		req:         r,
+		absPath:     absPath,
 		tmpFile:     tmpFile,
 		permissions: 0644,
 		uid:         fs.user.Uid,
@@ -153,16 +170,20 @@ func (fs *SftpServer) newFileWriter(r *sftp.Request) (io.WriterAt, error) {
 	}, nil
 }
 
-func (fs *SftpServer) removeEntry(r *sftp.Request) error {
-	return fs.deleteEntry(r.Filepath, false)
+func (fs *SftpServer) removeEntry(absPath string) error {
+	return fs.deleteEntry(absPath, false)
 }
 
-func (fs *SftpServer) renameEntry(r *sftp.Request) error {
-	if err := fs.checkFilePermission(r.Filepath, "rename"); err != nil {
+func (fs *SftpServer) renameEntry(absPath, absTarget string) error {
+	if err := fs.checkFilePermission(absPath, "rename"); err != nil {
+		return err
+	}
+	targetDir, _ := util.FullPath(absTarget).DirAndName()
+	if err := fs.checkFilePermission(targetDir, "write"); err != nil {
 		return err
 	}
-	oldDir, oldName := util.FullPath(r.Filepath).DirAndName()
-	newDir, newName := util.FullPath(r.Target).DirAndName()
+	oldDir, oldName := util.FullPath(absPath).DirAndName()
+	newDir, newName := util.FullPath(absTarget).DirAndName()
 	return fs.callWithClient(false, func(ctx context.Context, client filer_pb.SeaweedFilerClient) error {
 		_, err := client.AtomicRenameEntry(ctx, &filer_pb.AtomicRenameEntryRequest{
 			OldDirectory: oldDir, OldName: oldName,
@@ -172,15 +193,15 @@ func (fs *SftpServer) renameEntry(r *sftp.Request) error {
 	})
 }
 
-func (fs *SftpServer) setFileStat(r *sftp.Request) error {
-	if err := fs.checkFilePermission(r.Filepath, "write"); err != nil {
+func (fs *SftpServer) setFileStatWithRequest(absPath string, r *sftp.Request) error {
+	if err := fs.checkFilePermission(absPath, "write"); err != nil {
 		return err
 	}
-	entry, err := fs.getEntry(r.Filepath)
+	entry, err := fs.getEntry(absPath)
 	if err != nil {
 		return err
 	}
-	dir, _ := util.FullPath(r.Filepath).DirAndName()
+	dir, _ := util.FullPath(absPath).DirAndName()
 	// apply attrs
 	if r.AttrFlags().Permissions {
 		entry.Attributes.FileMode = uint32(r.Attributes().FileMode())
@@ -201,18 +222,22 @@ func (fs *SftpServer) setFileStat(r *sftp.Request) error {
 // ==================== Directory Operations ====================
 
 func (fs *SftpServer) listDir(r *sftp.Request) (sftp.ListerAt, error) {
-	if err := fs.checkFilePermission(r.Filepath, "list"); err != nil {
+	absPath, err := fs.toAbsolutePath(r.Filepath)
+	if err != nil {
+		return nil, err
+	}
+	if err := fs.checkFilePermission(absPath, "list"); err != nil {
 		return nil, err
 	}
 	if r.Method == "Stat" || r.Method == "Lstat" {
-		entry, err := fs.getEntry(r.Filepath)
+		entry, err := fs.getEntry(absPath)
 		if err != nil {
 			return nil, err
 		}
 		fi := &EnhancedFileInfo{FileInfo: FileInfoFromEntry(entry), uid: entry.Attributes.Uid, gid: entry.Attributes.Gid}
 		return listerat([]os.FileInfo{fi}), nil
 	}
-	return fs.listAllPages(r.Filepath)
+	return fs.listAllPages(absPath)
 }
 
 func (fs *SftpServer) listAllPages(dirPath string) (sftp.ListerAt, error) {
@@ -259,18 +284,19 @@ func (fs *SftpServer) fetchDirectoryPage(dirPath, start string) ([]os.FileInfo,
 }
 
 // makeDir creates a new directory with proper permissions.
-func (fs *SftpServer) makeDir(r *sftp.Request) error {
+func (fs *SftpServer) makeDir(absPath string) error {
 	if fs.user == nil {
 		return fmt.Errorf("cannot create directory: no user info")
 	}
-	dir, name := util.FullPath(r.Filepath).DirAndName()
-	if err := fs.checkFilePermission(r.Filepath, "mkdir"); err != nil {
+	dir, name := util.FullPath(absPath).DirAndName()
+	if err := fs.checkFilePermission(dir, "write"); err != nil {
 		return err
 	}
 	// default mode and ownership
 	err := filer_pb.Mkdir(context.Background(), fs, string(dir), name, func(entry *filer_pb.Entry) {
 		mode := uint32(0755 | os.ModeDir)
-		if strings.HasPrefix(r.Filepath, fs.user.HomeDir) {
+		// Defensive check: all paths should be under HomeDir after toAbsolutePath translation
+		if absPath == fs.user.HomeDir || strings.HasPrefix(absPath, fs.user.HomeDir+"/") {
 			mode = uint32(0700 | os.ModeDir)
 		}
 		entry.Attributes.FileMode = mode
@@ -288,8 +314,8 @@ func (fs *SftpServer) makeDir(r *sftp.Request) error {
 }
 
 // removeDir deletes a directory.
-func (fs *SftpServer) removeDir(r *sftp.Request) error {
-	return fs.deleteEntry(r.Filepath, false)
+func (fs *SftpServer) removeDir(absPath string) error {
+	return fs.deleteEntry(absPath, false)
 }
 
 func (fs *SftpServer) putFile(filepath string, reader io.Reader, user *user.User) error {
diff --git a/weed/sftpd/sftp_server.go b/weed/sftpd/sftp_server.go
index f158aeb64..e53098e6b 100644
--- a/weed/sftpd/sftp_server.go
+++ b/weed/sftpd/sftp_server.go
@@ -6,6 +6,8 @@ import (
 	"fmt"
 	"io"
 	"os"
+	"path"
+	"strings"
 	"time"
 
 	"github.com/pkg/sftp"
@@ -37,6 +39,28 @@ func NewSftpServer(filerAddr pb.ServerAddress, grpcDialOption grpc.DialOption, d
 	}
 }
 
+// toAbsolutePath translates a user-relative path to an absolute filer path.
+// When a user has HomeDir="/sftp/user", their view of "/" maps to "/sftp/user".
+// This implements chroot-like behavior where the user's home directory
+// becomes their root.
+func (fs *SftpServer) toAbsolutePath(userPath string) (string, error) {
+	// If user has root as home directory, no translation needed
+	if fs.user.HomeDir == "" || fs.user.HomeDir == "/" {
+		return path.Clean(userPath), nil
+	}
+
+	// Concatenate home directory with user path, then clean to resolve any ".." components
+	p := path.Join(fs.user.HomeDir, strings.TrimPrefix(userPath, "/"))
+
+	// Security check: ensure the final path is within the home directory.
+	// This prevents path traversal attacks like `../..` that could escape the chroot jail.
+	if !strings.HasPrefix(p, fs.user.HomeDir+"/") && p != fs.user.HomeDir {
+		return "", fmt.Errorf("path traversal attempt: %s resolves to %s which is outside home dir %s", userPath, p, fs.user.HomeDir)
+	}
+
+	return p, nil
+}
+
 // Fileread is invoked for “get” requests.
 func (fs *SftpServer) Fileread(req *sftp.Request) (io.ReaderAt, error) {
 	return fs.readFile(req)
diff --git a/weed/sftpd/sftp_server_test.go b/weed/sftpd/sftp_server_test.go
new file mode 100644
index 000000000..0af94ca14
--- /dev/null
+++ b/weed/sftpd/sftp_server_test.go
@@ -0,0 +1,103 @@
+package sftpd
+
+import (
+	"testing"
+
+	"github.com/seaweedfs/seaweedfs/weed/sftpd/user"
+	"github.com/stretchr/testify/assert"
+)
+
+func stringPtr(s string) *string {
+	return &s
+}
+
+func TestToAbsolutePath(t *testing.T) {
+	tests := []struct {
+		name        string
+		homeDir     *string // Use pointer to distinguish between unset and empty
+		userPath    string
+		expected    string
+		expectError bool
+	}{
+		{
+			name:     "normal path",
+			userPath: "/foo.txt",
+			expected: "/sftp/testuser/foo.txt",
+		},
+		{
+			name:     "root path",
+			userPath: "/",
+			expected: "/sftp/testuser",
+		},
+		{
+			name:     "path with dot",
+			userPath: "/./foo.txt",
+			expected: "/sftp/testuser/foo.txt",
+		},
+		{
+			name:        "path traversal attempts",
+			userPath:    "/../foo.txt",
+			expectError: true,
+		},
+		{
+			name:        "path traversal attempts 2",
+			userPath:    "../../foo.txt",
+			expectError: true,
+		},
+		{
+			name:        "path traversal attempts 3",
+			userPath:    "/subdir/../../foo.txt",
+			expectError: true,
+		},
+		{
+			name:     "empty path",
+			userPath: "",
+			expected: "/sftp/testuser",
+		},
+		{
+			name:     "multiple slashes",
+			userPath: "//foo.txt",
+			expected: "/sftp/testuser/foo.txt",
+		},
+		{
+			name:     "trailing slash",
+			userPath: "/foo/",
+			expected: "/sftp/testuser/foo",
+		},
+		{
+			name:     "empty HomeDir passthrough",
+			homeDir:  stringPtr(""),
+			userPath: "/foo.txt",
+			expected: "/foo.txt",
+		},
+		{
+			name:     "root HomeDir passthrough",
+			homeDir:  stringPtr("/"),
+			userPath: "/foo.txt",
+			expected: "/foo.txt",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			homeDir := "/sftp/testuser" // default
+			if tt.homeDir != nil {
+				homeDir = *tt.homeDir
+			}
+
+			fs := &SftpServer{
+				user: &user.User{
+					HomeDir: homeDir,
+				},
+			}
+
+			got, err := fs.toAbsolutePath(tt.userPath)
+			if tt.expectError {
+				assert.Error(t, err)
+			} else {
+				assert.NoError(t, err)
+				assert.Equal(t, tt.expected, got)
+			}
+		})
+	}
+}
diff --git a/weed/sftpd/sftp_service.go b/weed/sftpd/sftp_service.go
index e50bd87ba..4d21815a9 100644
--- a/weed/sftpd/sftp_service.go
+++ b/weed/sftpd/sftp_service.go
@@ -284,8 +284,8 @@ func (s *SFTPService) handleChannel(newChannel ssh.NewChannel, fs *SftpServer) {
 
 // handleSFTP starts the SFTP server on the SSH channel.
 func (s *SFTPService) handleSFTP(channel ssh.Channel, fs *SftpServer) {
-	// Create server options with initial working directory set to user's home
-	serverOptions := sftp.WithStartDirectory(fs.user.HomeDir)
+	// Start at virtual root "/" - toAbsolutePath translates this to the user's HomeDir
+	serverOptions := sftp.WithStartDirectory("/")
 	server := sftp.NewRequestServer(channel, sftp.Handlers{
 		FileGet:  fs,
 		FilePut:  fs,
diff --git a/weed/sftpd/user/filestore.go b/weed/sftpd/user/filestore.go
index c522a388a..4c372aa76 100644
--- a/weed/sftpd/user/filestore.go
+++ b/weed/sftpd/user/filestore.go
@@ -5,6 +5,7 @@ import (
 	"encoding/json"
 	"fmt"
 	"os"
+	"path"
 	"sync"
 
 	"golang.org/x/crypto/ssh"
@@ -99,6 +100,10 @@ func (s *FileStore) loadUsers() error {
 				user.PublicKeys[i] = string(pubKey.Marshal())
 			}
 		}
+		// Clean HomeDir to handle trailing slashes and normalize path
+		if user.HomeDir != "" {
+			user.HomeDir = path.Clean(user.HomeDir)
+		}
 		s.users[user.Username] = user
 
 	}