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All rights reserved. + +Redistribution and use in source and binary forms, with or without +modification, are permitted provided that the following conditions are +met: + + * Redistributions of source code must retain the above copyright +notice, this list of conditions and the following disclaimer. + * Redistributions in binary form must reproduce the above +copyright notice, this list of conditions and the following disclaimer +in the documentation and/or other materials provided with the +distribution. + * Neither the name of Google Inc. nor the names of its +contributors may be used to endorse or promote products derived from +this software without specific prior written permission. + +THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS +"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT +LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR +A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT +OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, +SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT +LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, +DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY +THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT +(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE +OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. diff --git a/pkg/symlink/MAINTAINERS b/pkg/symlink/MAINTAINERS index 68a97d2fc2..51a41a5b60 100644 --- a/pkg/symlink/MAINTAINERS +++ b/pkg/symlink/MAINTAINERS @@ -1,2 +1,3 @@ -Michael Crosby (@crosbymichael) -Victor Vieux (@vieux) +Tibor Vass (@tiborvass) +Cristian Staretu (@unclejack) +Tianon Gravi (@tianon) diff --git a/pkg/symlink/README.md b/pkg/symlink/README.md new file mode 100644 index 0000000000..0d1dbb70e6 --- /dev/null +++ b/pkg/symlink/README.md @@ -0,0 +1,5 @@ +Package symlink implements EvalSymlinksInScope which is an extension of filepath.EvalSymlinks +from the [Go standard library](https://golang.org/pkg/path/filepath). + +The code from filepath.EvalSymlinks has been adapted in fs.go. +Please read the LICENSE.BSD file that governs fs.go and LICENSE.APACHE for fs_test.go. diff --git a/pkg/symlink/fs.go b/pkg/symlink/fs.go index 6ce99c6bda..b4bdff24dd 100644 --- a/pkg/symlink/fs.go +++ b/pkg/symlink/fs.go @@ -1,101 +1,131 @@ +// Copyright 2012 The Go Authors. All rights reserved. +// Use of this source code is governed by a BSD-style +// license that can be found in the LICENSE.BSD file. + +// This code is a modified version of path/filepath/symlink.go from the Go standard library. + package symlink import ( - "fmt" + "bytes" + "errors" "os" - "path" "path/filepath" "strings" ) -const maxLoopCounter = 100 - -// FollowSymlink will follow an existing link and scope it to the root -// path provided. -// The role of this function is to return an absolute path in the root -// or normalize to the root if the symlink leads to a path which is -// outside of the root. -// Errors encountered while attempting to follow the symlink in path -// will be reported. -// Normalizations to the root don't constitute errors. -func FollowSymlinkInScope(link, root string) (string, error) { - root, err := filepath.Abs(root) +// FollowSymlinkInScope is a wrapper around evalSymlinksInScope that returns an absolute path +func FollowSymlinkInScope(path, root string) (string, error) { + path, err := filepath.Abs(path) if err != nil { return "", err } - - link, err = filepath.Abs(link) + root, err = filepath.Abs(root) if err != nil { return "", err } - - if link == root { - return root, nil - } - - if !strings.HasPrefix(filepath.Dir(link), root) { - return "", fmt.Errorf("%s is not within %s", link, root) - } - - prev := "/" - - for _, p := range strings.Split(link, "/") { - prev = filepath.Join(prev, p) - - loopCounter := 0 - for { - loopCounter++ - - if loopCounter >= maxLoopCounter { - return "", fmt.Errorf("loopCounter reached MAX: %v", loopCounter) - } - - if !strings.HasPrefix(prev, root) { - // Don't resolve symlinks outside of root. For example, - // we don't have to check /home in the below. - // - // /home -> usr/home - // FollowSymlinkInScope("/home/bob/foo/bar", "/home/bob/foo") - break - } - - stat, err := os.Lstat(prev) - if err != nil { - if os.IsNotExist(err) { - break - } - return "", err - } - - // let's break if we're not dealing with a symlink - if stat.Mode()&os.ModeSymlink != os.ModeSymlink { - break - } - - // process the symlink - dest, err := os.Readlink(prev) - if err != nil { - return "", err - } - - if path.IsAbs(dest) { - prev = filepath.Join(root, dest) - } else { - prev, _ = filepath.Abs(prev) - - dir := filepath.Dir(prev) - prev = filepath.Join(dir, dest) - if dir == root && !strings.HasPrefix(prev, root) { - prev = root - } - if len(prev) < len(root) || (len(prev) == len(root) && prev != root) { - prev = filepath.Join(root, filepath.Base(dest)) - } - } - } - } - if prev == "/" { - prev = root - } - return prev, nil + return evalSymlinksInScope(path, root) +} + +// evalSymlinksInScope will evaluate symlinks in `path` within a scope `root` and return +// a result guaranteed to be contained within the scope `root`, at the time of the call. +// Symlinks in `root` are not evaluated and left as-is. +// Errors encountered while attempting to evaluate symlinks in path will be returned. +// Non-existing paths are valid and do not constitute an error. +// `path` has to contain `root` as a prefix, or else an error will be returned. +// Trying to break out from `root` does not constitute an error. +// +// Example: +// If /foo/bar -> /outside, +// FollowSymlinkInScope("/foo/bar", "/foo") == "/foo/outside" instead of "/oustide" +// +// IMPORTANT: it is the caller's responsibility to call evalSymlinksInScope *after* relevant symlinks +// are created and not to create subsequently, additional symlinks that could potentially make a +// previously-safe path, unsafe. Example: if /foo/bar does not exist, evalSymlinksInScope("/foo/bar", "/foo") +// would return "/foo/bar". If one makes /foo/bar a symlink to /baz subsequently, then "/foo/bar" should +// no longer be considered safely contained in "/foo". +func evalSymlinksInScope(path, root string) (string, error) { + root = filepath.Clean(root) + if path == root { + return path, nil + } + if !strings.HasPrefix(path, root) { + return "", errors.New("evalSymlinksInScope: " + path + " is not in " + root) + } + const maxIter = 255 + originalPath := path + // given root of "/a" and path of "/a/b/../../c" we want path to be "/b/../../c" + path = path[len(root):] + if root == string(filepath.Separator) { + path = string(filepath.Separator) + path + } + if !strings.HasPrefix(path, string(filepath.Separator)) { + return "", errors.New("evalSymlinksInScope: " + path + " is not in " + root) + } + path = filepath.Clean(path) + // consume path by taking each frontmost path element, + // expanding it if it's a symlink, and appending it to b + var b bytes.Buffer + // b here will always be considered to be the "current absolute path inside + // root" when we append paths to it, we also append a slash and use + // filepath.Clean after the loop to trim the trailing slash + for n := 0; path != ""; n++ { + if n > maxIter { + return "", errors.New("evalSymlinksInScope: too many links in " + originalPath) + } + + // find next path component, p + i := strings.IndexRune(path, filepath.Separator) + var p string + if i == -1 { + p, path = path, "" + } else { + p, path = path[:i], path[i+1:] + } + + if p == "" { + continue + } + + // this takes a b.String() like "b/../" and a p like "c" and turns it + // into "/b/../c" which then gets filepath.Cleaned into "/c" and then + // root gets prepended and we Clean again (to remove any trailing slash + // if the first Clean gave us just "/") + cleanP := filepath.Clean(string(filepath.Separator) + b.String() + p) + if cleanP == string(filepath.Separator) { + // never Lstat "/" itself + b.Reset() + continue + } + fullP := filepath.Clean(root + cleanP) + + fi, err := os.Lstat(fullP) + if os.IsNotExist(err) { + // if p does not exist, accept it + b.WriteString(p) + b.WriteRune(filepath.Separator) + continue + } + if err != nil { + return "", err + } + if fi.Mode()&os.ModeSymlink == 0 { + b.WriteString(p + string(filepath.Separator)) + continue + } + + // it's a symlink, put it at the front of path + dest, err := os.Readlink(fullP) + if err != nil { + return "", err + } + if filepath.IsAbs(dest) { + b.Reset() + } + path = dest + string(filepath.Separator) + path + } + + // see note above on "fullP := ..." for why this is double-cleaned and + // what's happening here + return filepath.Clean(root + filepath.Clean(string(filepath.Separator)+b.String())), nil } diff --git a/pkg/symlink/fs_test.go b/pkg/symlink/fs_test.go index 0e2f948b6a..24ffb1e7c7 100644 --- a/pkg/symlink/fs_test.go +++ b/pkg/symlink/fs_test.go @@ -1,3 +1,5 @@ +// Licensed under the Apache License, Version 2.0; See LICENSE.APACHE + package symlink import (