Fail to start server if detected cross-device mounts. (#4807)

Fixes #4764

pkg/mountinfo/mountinfo_linux.go

@@ -0,0 +1,131 @@
+// +build linux
+
+/*
+ * Minio Cloud Storage, (C) 2017 Minio, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package mountinfo
+
+import (
+	"bufio"
+	"fmt"
+	"io"
+	"os"
+	"path/filepath"
+	"strconv"
+	"strings"
+)
+
+const (
+	// Number of fields per line in /proc/mounts as per the fstab man page.
+	expectedNumFieldsPerLine = 6
+	// Location of the mount file to use
+	procMountsPath = "/proc/mounts"
+)
+
+// CheckCrossDevice - check if any list of paths has any sub-mounts at /proc/mounts.
+func CheckCrossDevice(absPaths []string) error {
+	return checkCrossDevice(absPaths, procMountsPath)
+}
+
+// Check cross device is an internal function.
+func checkCrossDevice(absPaths []string, mountsPath string) error {
+	mounts, err := readProcMounts(mountsPath)
+	if err != nil {
+		return err
+	}
+	for _, path := range absPaths {
+		if err := mounts.checkCrossMounts(path); err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+// CheckCrossDevice - check if given path has any sub-mounts in the input mounts list.
+func (mts mountInfos) checkCrossMounts(path string) error {
+	if !filepath.IsAbs(path) {
+		return fmt.Errorf("Invalid argument, path (%s) is expected to be absolute", path)
+	}
+	var crossMounts mountInfos
+	for _, mount := range mts {
+		// Add a separator to indicate that this is a proper mount-point.
+		// This is to avoid a situation where prefix is '/tmp/fsmount'
+		// and mount path is /tmp/fs. In such a scenario we need to check for
+		// `/tmp/fs/` to be a common prefix amount other mounts.
+		mpath := strings.TrimSuffix(mount.Path, "/") + "/"
+		ppath := strings.TrimSuffix(path, "/") + "/"
+		if strings.HasPrefix(mpath, ppath) {
+			// At this point if the mount point has a common prefix two conditions can happen.
+			// - mount.Path matches exact with `path` means we can proceed no error here.
+			// - mount.Path doesn't match (means cross-device mount), should error out.
+			if mount.Path != path {
+				crossMounts = append(crossMounts, mount)
+			}
+		}
+	}
+	msg := `Cross-device mounts detected on path (%s) at following locations %s. Export path should not have any sub-mounts, refusing to start.`
+	if len(crossMounts) > 0 {
+		// if paths didn't match then we do have cross-device mount.
+		return fmt.Errorf(msg, path, crossMounts)
+	}
+	return nil
+}
+
+// readProcMounts reads the given mountFilePath (normally /proc/mounts) and produces a hash
+// of the contents.  If the out argument is not nil, this fills it with MountPoint structs.
+func readProcMounts(mountFilePath string) (mountInfos, error) {
+	file, err := os.Open(mountFilePath)
+	if err != nil {
+		return nil, err
+	}
+	defer file.Close()
+	return parseMountFrom(file)
+}
+
+func parseMountFrom(file io.Reader) (mountInfos, error) {
+	var mounts = mountInfos{}
+	scanner := bufio.NewReader(file)
+	for {
+		line, err := scanner.ReadString('\n')
+		if err == io.EOF {
+			break
+		}
+		fields := strings.Fields(line)
+		if len(fields) != expectedNumFieldsPerLine {
+			return nil, fmt.Errorf("wrong number of fields (expected %d, got %d): %s", expectedNumFieldsPerLine, len(fields), line)
+		}
+
+		// Freq should be an integer.
+		if _, err := strconv.Atoi(fields[4]); err != nil {
+			return nil, err
+		}
+
+		// Pass should be an integer.
+		if _, err := strconv.Atoi(fields[5]); err != nil {
+			return nil, err
+		}
+
+		mounts = append(mounts, mountInfo{
+			Device:  fields[0],
+			Path:    fields[1],
+			FSType:  fields[2],
+			Options: strings.Split(fields[3], ","),
+			Freq:    fields[4],
+			Pass:    fields[5],
+		})
+	}
+	return mounts, nil
+}