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authorbaude <bbaude@redhat.com>2018-10-24 10:39:12 -0500
committerbaude <bbaude@redhat.com>2018-10-25 06:42:43 -0500
commit6246942d377bd9ed665a4ac448120352454dd83d (patch)
treef99794cbb171220c8ac6ff7c0008381062a6b6df /vendor/github.com/cyphar/filepath-securejoin/join.go
parent57f778aed93efc0961b1335bcd07c3c82a11da0a (diff)
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Increase security and performance when looking up groups
We implement the securejoin method to make sure the paths to /etc/passwd and /etc/group are not symlinks to something naughty or outside the container image. And then instead of actually chrooting, we use the runc functions to get information about a user. The net result is increased security and a a performance gain from 41ms to 100us. Signed-off-by: baude <bbaude@redhat.com>
Diffstat (limited to 'vendor/github.com/cyphar/filepath-securejoin/join.go')
-rw-r--r--vendor/github.com/cyphar/filepath-securejoin/join.go134
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diff --git a/vendor/github.com/cyphar/filepath-securejoin/join.go b/vendor/github.com/cyphar/filepath-securejoin/join.go
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+// Copyright (C) 2014-2015 Docker Inc & Go Authors. All rights reserved.
+// Copyright (C) 2017 SUSE LLC. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Package securejoin is an implementation of the hopefully-soon-to-be-included
+// SecureJoin helper that is meant to be part of the "path/filepath" package.
+// The purpose of this project is to provide a PoC implementation to make the
+// SecureJoin proposal (https://github.com/golang/go/issues/20126) more
+// tangible.
+package securejoin
+
+import (
+ "bytes"
+ "os"
+ "path/filepath"
+ "strings"
+ "syscall"
+
+ "github.com/pkg/errors"
+)
+
+// ErrSymlinkLoop is returned by SecureJoinVFS when too many symlinks have been
+// evaluated in attempting to securely join the two given paths.
+var ErrSymlinkLoop = errors.Wrap(syscall.ELOOP, "secure join")
+
+// IsNotExist tells you if err is an error that implies that either the path
+// accessed does not exist (or path components don't exist). This is
+// effectively a more broad version of os.IsNotExist.
+func IsNotExist(err error) bool {
+ // If it's a bone-fide ENOENT just bail.
+ if os.IsNotExist(errors.Cause(err)) {
+ return true
+ }
+
+ // Check that it's not actually an ENOTDIR, which in some cases is a more
+ // convoluted case of ENOENT (usually involving weird paths).
+ var errno error
+ switch err := errors.Cause(err).(type) {
+ case *os.PathError:
+ errno = err.Err
+ case *os.LinkError:
+ errno = err.Err
+ case *os.SyscallError:
+ errno = err.Err
+ }
+ return errno == syscall.ENOTDIR || errno == syscall.ENOENT
+}
+
+// SecureJoinVFS joins the two given path components (similar to Join) except
+// that the returned path is guaranteed to be scoped inside the provided root
+// path (when evaluated). Any symbolic links in the path are evaluated with the
+// given root treated as the root of the filesystem, similar to a chroot. The
+// filesystem state is evaluated through the given VFS interface (if nil, the
+// standard os.* family of functions are used).
+//
+// Note that the guarantees provided by this function only apply if the path
+// components in the returned string are not modified (in other words are not
+// replaced with symlinks on the filesystem) after this function has returned.
+// Such a symlink race is necessarily out-of-scope of SecureJoin.
+func SecureJoinVFS(root, unsafePath string, vfs VFS) (string, error) {
+ // Use the os.* VFS implementation if none was specified.
+ if vfs == nil {
+ vfs = osVFS{}
+ }
+
+ var path bytes.Buffer
+ n := 0
+ for unsafePath != "" {
+ if n > 255 {
+ return "", ErrSymlinkLoop
+ }
+
+ // Next path component, p.
+ i := strings.IndexRune(unsafePath, filepath.Separator)
+ var p string
+ if i == -1 {
+ p, unsafePath = unsafePath, ""
+ } else {
+ p, unsafePath = unsafePath[:i], unsafePath[i+1:]
+ }
+
+ // Create a cleaned path, using the lexical semantics of /../a, to
+ // create a "scoped" path component which can safely be joined to fullP
+ // for evaluation. At this point, path.String() doesn't contain any
+ // symlink components.
+ cleanP := filepath.Clean(string(filepath.Separator) + path.String() + p)
+ if cleanP == string(filepath.Separator) {
+ path.Reset()
+ continue
+ }
+ fullP := filepath.Clean(root + cleanP)
+
+ // Figure out whether the path is a symlink.
+ fi, err := vfs.Lstat(fullP)
+ if err != nil && !IsNotExist(err) {
+ return "", err
+ }
+ // Treat non-existent path components the same as non-symlinks (we
+ // can't do any better here).
+ if IsNotExist(err) || fi.Mode()&os.ModeSymlink == 0 {
+ path.WriteString(p)
+ path.WriteRune(filepath.Separator)
+ continue
+ }
+
+ // Only increment when we actually dereference a link.
+ n++
+
+ // It's a symlink, expand it by prepending it to the yet-unparsed path.
+ dest, err := vfs.Readlink(fullP)
+ if err != nil {
+ return "", err
+ }
+ // Absolute symlinks reset any work we've already done.
+ if filepath.IsAbs(dest) {
+ path.Reset()
+ }
+ unsafePath = dest + string(filepath.Separator) + unsafePath
+ }
+
+ // We have to clean path.String() here because it may contain '..'
+ // components that are entirely lexical, but would be misleading otherwise.
+ // And finally do a final clean to ensure that root is also lexically
+ // clean.
+ fullP := filepath.Clean(string(filepath.Separator) + path.String())
+ return filepath.Clean(root + fullP), nil
+}
+
+// SecureJoin is a wrapper around SecureJoinVFS that just uses the os.* library
+// of functions as the VFS. If in doubt, use this function over SecureJoinVFS.
+func SecureJoin(root, unsafePath string) (string, error) {
+ return SecureJoinVFS(root, unsafePath, nil)
+}