103 lines
2.2 KiB
Go
103 lines
2.2 KiB
Go
package symlink
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import (
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"fmt"
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"os"
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"path"
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"path/filepath"
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"strings"
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)
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const maxLoopCounter = 100
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type ErrBreakout error
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// FollowSymlink will follow an existing link and scope it to the root
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// path provided.
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// The role of this function is to return an absolute path in the root
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// or normalize to the root if the symlink leads to a path which is
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// outside of the root.
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// Errors encountered while attempting to follow the symlink in path
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// will be reported.
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// Normalizations to the root don't constitute errors.
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func FollowSymlinkInScope(link, root string) (string, error) {
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root, err := filepath.Abs(root)
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if err != nil {
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return "", err
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}
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link, err = filepath.Abs(link)
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if err != nil {
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return "", err
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}
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if link == root {
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return root, nil
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}
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if !strings.HasPrefix(filepath.Dir(link), root) {
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return "", ErrBreakout(fmt.Errorf("%s is not within %s", link, root))
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}
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prev := "/"
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for _, p := range strings.Split(link, "/") {
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prev = filepath.Join(prev, p)
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loopCounter := 0
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for {
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loopCounter++
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if loopCounter >= maxLoopCounter {
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return "", fmt.Errorf("loopCounter reached MAX: %v", loopCounter)
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}
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if !strings.HasPrefix(prev, root) {
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// Don't resolve symlinks outside of root. For example,
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// we don't have to check /home in the below.
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//
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// /home -> usr/home
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// FollowSymlinkInScope("/home/bob/foo/bar", "/home/bob/foo")
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break
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}
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stat, err := os.Lstat(prev)
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if err != nil {
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if os.IsNotExist(err) {
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break
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}
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return "", err
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}
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// let's break if we're not dealing with a symlink
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if stat.Mode()&os.ModeSymlink != os.ModeSymlink {
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break
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}
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// process the symlink
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dest, err := os.Readlink(prev)
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if err != nil {
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return "", err
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}
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if path.IsAbs(dest) {
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prev = filepath.Join(root, dest)
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} else {
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prev, _ = filepath.Abs(prev)
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dir := filepath.Dir(prev)
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prev = filepath.Join(dir, dest)
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if dir == root && !strings.HasPrefix(prev, root) {
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prev = root
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}
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if len(prev) < len(root) || (len(prev) == len(root) && prev != root) {
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prev = filepath.Join(root, filepath.Base(dest))
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}
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}
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}
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}
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if prev == "/" {
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prev = root
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}
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return prev, nil
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}
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