[release-branch.go1.20] path/filepath: do not Clean("a/../c:/b") into c:\b on Windows

Do not permit Clean to convert a relative path into one starting
with a drive reference. This change causes Clean to insert a .
path element at the start of a path when the original path does not
start with a volume name, and the first path element would contain
a colon.

This may introduce a spurious but harmless . path element under
some circumstances. For example, Clean("a/../b:/../c") becomes `.\c`.

This reverts CL 401595, since the change here supersedes the one
in that CL.

Thanks to RyotaK (https://twitter.com/ryotkak) for reporting this issue.

Updates #57274
Fixes #57276
Fixes CVE-2022-41722

Change-Id: I837446285a03aa74c79d7642720e01f354c2ca17
Reviewed-on: https://team-review.git.corp.google.com/c/golang/go-private/+/1675249
Reviewed-by: Roland Shoemaker <bracewell@google.com>
Run-TryBot: Damien Neil <dneil@google.com>
Reviewed-by: Julie Qiu <julieqiu@google.com>
TryBot-Result: Security TryBots <security-trybots@go-security-trybots.iam.gserviceaccount.com>
(cherry picked from commit 8ca37f4813ef2f64600c92b83f17c9f3ca6c03a5)
Reviewed-on: https://team-review.git.corp.google.com/c/golang/go-private/+/1728944
Run-TryBot: Roland Shoemaker <bracewell@google.com>
Reviewed-by: Tatiana Bradley <tatianabradley@google.com>
Reviewed-by: Damien Neil <dneil@google.com>
Reviewed-on: https://go-review.googlesource.com/c/go/+/468119
Reviewed-by: Than McIntosh <thanm@google.com>
Run-TryBot: Michael Pratt <mpratt@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Auto-Submit: Michael Pratt <mpratt@google.com>

diff --git a/src/path/filepath/path.go b/src/path/filepath/path.go
index a6578cbb728b95462b50da148a2342ba74e9faf7..32dd887998650bff7cff4456c1ea1e023fcaa522 100644 (file)
--- a/src/path/filepath/path.go
+++ b/src/path/filepath/path.go
@@ -15,6 +15,7 @@ import (
        "errors"
        "io/fs"
        "os"
+       "runtime"
        "sort"
        "strings"
 )
@@ -117,21 +118,9 @@ func Clean(path string) string {
                case os.IsPathSeparator(path[r]):
                        // empty path element
                        r++
-               case path[r] == '.' && r+1 == n:
+               case path[r] == '.' && (r+1 == n || os.IsPathSeparator(path[r+1])):
                        // . element
                        r++
-               case path[r] == '.' && os.IsPathSeparator(path[r+1]):
-                       // ./ element
-                       r++
-
-                       for r < len(path) && os.IsPathSeparator(path[r]) {
-                               r++
-                       }
-                       if out.w == 0 && volumeNameLen(path[r:]) > 0 {
-                               // When joining prefix "." and an absolute path on Windows,
-                               // the prefix should not be removed.
-                               out.append('.')
-                       }
                case path[r] == '.' && path[r+1] == '.' && (r+2 == n || os.IsPathSeparator(path[r+2])):
                        // .. element: remove to last separator
                        r += 2
@@ -157,6 +146,18 @@ func Clean(path string) string {
                        if rooted && out.w != 1 || !rooted && out.w != 0 {
                                out.append(Separator)
                        }
+                       // If a ':' appears in the path element at the start of a Windows path,
+                       // insert a .\ at the beginning to avoid converting relative paths
+                       // like a/../c: into c:.
+                       if runtime.GOOS == "windows" && out.w == 0 && out.volLen == 0 && r != 0 {
+                               for i := r; i < n && !os.IsPathSeparator(path[i]); i++ {
+                                       if path[i] == ':' {
+                                               out.append('.')
+                                               out.append(Separator)
+                                               break
+                                       }
+                               }
+                       }
                        // copy element
                        for ; r < n && !os.IsPathSeparator(path[r]); r++ {
                                out.append(path[r])

diff --git a/src/path/filepath/path_test.go b/src/path/filepath/path_test.go
index 66474448526675cea863ddbadae5fd2fb693934d..697bcc672d73c300482e335eeee3523cd82721a8 100644 (file)
--- a/src/path/filepath/path_test.go
+++ b/src/path/filepath/path_test.go
@@ -106,6 +106,13 @@ var wincleantests = []PathTest{
        {`//abc`, `\\abc`},
        {`///abc`, `\\\abc`},
        {`//abc//`, `\\abc\\`},
+
+       // Don't allow cleaning to move an element with a colon to the start of the path.
+       {`a/../c:`, `.\c:`},
+       {`a\..\c:`, `.\c:`},
+       {`a/../c:/a`, `.\c:\a`},
+       {`a/../../c:`, `..\c:`},
+       {`foo:bar`, `foo:bar`},
 }
 
 func TestClean(t *testing.T) {
@@ -174,6 +181,7 @@ var winislocaltests = []IsLocalTest{
        {`C:`, false},
        {`C:\a`, false},
        {`..\a`, false},
+       {`a/../c:`, false},
        {`CONIN$`, false},
        {`conin$`, false},
        {`CONOUT$`, false},

diff --git a/src/path/filepath/path_windows_test.go b/src/path/filepath/path_windows_test.go
index e37dddceadbdf1510ee0df7eaf7dba9fc04358b0..c8c7eefcc0bb4bd2ff193001cded0b7892893e54 100644 (file)
--- a/src/path/filepath/path_windows_test.go
+++ b/src/path/filepath/path_windows_test.go
@@ -542,7 +542,7 @@ func TestIssue52476(t *testing.T) {
        }{
                {`..\.`, `C:`, `..\C:`},
                {`..`, `C:`, `..\C:`},
-               {`.`, `:`, `:`},
+               {`.`, `:`, `.\:`},
                {`.`, `C:`, `.\C:`},
                {`.`, `C:/a/b/../c`, `.\C:\a\c`},
                {`.`, `\C:`, `.\C:`},