Author: Ben Hutchings <ben@decadent.org.uk>
Date: Tue, 19 May 2015 02:38:40 +0100
Description: Delay creation of symlinks to prevent arbitrary file writes (CVE-2015-1038)
Bug: http://sourceforge.net/p/p7zip/bugs/147/
Bug-Debian: https://bugs.debian.org/774660

Alexander Cherepanov discovered that 7zip is susceptible to a
directory traversal vulnerability.  While extracting an archive, it
will extract symlinks and then follow them if they are referenced in
further entries.  This can be exploited by a rogue archive to write
files outside the current directory.

We have to create placeholder files (which we already do) and delay
creating symlinks until the end of extraction.

Due to the possibility of anti-items (deletions) in the archive, it is
possible for placeholders to be deleted and replaced before we create
the symlinks.  It's not clear that this can be used for mischief, but
GNU tar guards against similar problems by checking that the placeholder
still exists and is the same inode.  XXX It also checks 'birth time' but
this isn't portable.  We can probably get away with comparing ctime
since we don't support hard links.

diff -rup p7zip_15.09.orig/CPP/7zip/UI/Agent/Agent.cpp p7zip_15.09/CPP/7zip/UI/Agent/Agent.cpp
--- p7zip_15.09.orig/CPP/7zip/UI/Agent/Agent.cpp	2015-09-17 20:02:35.000000000 +0100
+++ p7zip_15.09/CPP/7zip/UI/Agent/Agent.cpp	2015-12-03 02:22:47.073724194 +0000
@@ -1515,7 +1515,7 @@ STDMETHODIMP CAgentFolder::Extract(const
   HRESULT result = _agentSpec->GetArchive()->Extract(&realIndices.Front(),
       realIndices.Size(), testMode, extractCallback);
   if (result == S_OK)
-    result = extractCallbackSpec->SetDirsTimes();
+    result = extractCallbackSpec->SetFinalAttribs();
   return result;
   COM_TRY_END
 }
diff -rup p7zip_15.09.orig/CPP/7zip/UI/Client7z/Client7z.cpp p7zip_15.09/CPP/7zip/UI/Client7z/Client7z.cpp
--- p7zip_15.09.orig/CPP/7zip/UI/Client7z/Client7z.cpp	2015-10-17 15:52:30.000000000 +0100
+++ p7zip_15.09/CPP/7zip/UI/Client7z/Client7z.cpp	2015-12-03 02:22:47.073724194 +0000
@@ -230,8 +230,11 @@ private:
   COutFileStream *_outFileStreamSpec;
   CMyComPtr<ISequentialOutStream> _outFileStream;
 
+  CObjectVector<NWindows::NFile::NDir::CDelayedSymLink> _delayedSymLinks;
+
 public:
   void Init(IInArchive *archiveHandler, const FString &directoryPath);
+  HRESULT SetFinalAttribs();
 
   UInt64 NumErrors;
   bool PasswordIsDefined;
@@ -449,11 +452,23 @@ STDMETHODIMP CArchiveExtractCallback::Se
   }
   _outFileStream.Release();
   if (_extractMode && _processedFileInfo.AttribDefined)
-    SetFileAttrib(_diskFilePath, _processedFileInfo.Attrib);
+    SetFileAttrib(_diskFilePath, _processedFileInfo.Attrib, &_delayedSymLinks);
   PrintNewLine();
   return S_OK;
 }
 
+HRESULT CArchiveExtractCallback::SetFinalAttribs()
+{
+  HRESULT result = S_OK;
+
+  for (int i = 0; i != _delayedSymLinks.Size(); ++i)
+    if (!_delayedSymLinks[i].Create())
+      result = E_FAIL;
+
+  _delayedSymLinks.Clear();
+
+  return result;
+}
 
 STDMETHODIMP CArchiveExtractCallback::CryptoGetTextPassword(BSTR *password)
 {
@@ -914,6 +929,8 @@ int MY_CDECL main(int numArgs, const cha
       // extractCallbackSpec->PasswordIsDefined = true;
       // extractCallbackSpec->Password = L"1";
       HRESULT result = archive->Extract(NULL, (UInt32)(Int32)(-1), false, extractCallback);
+      if (result == S_OK)
+	result = extractCallbackSpec->SetFinalAttribs();
       if (result != S_OK)
       {
         PrintError("Extract Error");
diff -rup p7zip_15.09.orig/CPP/7zip/UI/Common/ArchiveExtractCallback.cpp p7zip_15.09/CPP/7zip/UI/Common/ArchiveExtractCallback.cpp
--- p7zip_15.09.orig/CPP/7zip/UI/Common/ArchiveExtractCallback.cpp	2015-10-03 09:49:15.000000000 +0100
+++ p7zip_15.09/CPP/7zip/UI/Common/ArchiveExtractCallback.cpp	2015-12-03 02:24:40.444963545 +0000
@@ -1502,7 +1502,7 @@ STDMETHODIMP CArchiveExtractCallback::Se
     NumFiles++;
 
   if (!_stdOutMode && _extractMode && _fi.AttribDefined)
-    SetFileAttrib(_diskFilePath, _fi.Attrib);
+    SetFileAttrib(_diskFilePath, _fi.Attrib, &_delayedSymLinks);
   
   RINOK(_extractCallback2->SetOperationResult(opRes, BoolToInt(_encrypted)));
   
@@ -1584,8 +1584,9 @@ static unsigned GetNumSlashes(const FCha
   }
 }
 
-HRESULT CArchiveExtractCallback::SetDirsTimes()
+HRESULT CArchiveExtractCallback::SetFinalAttribs()
 {
+  HRESULT result = S_OK;
   CRecordVector<CExtrRefSortPair> pairs;
   pairs.ClearAndSetSize(_extractedFolderPaths.Size());
   unsigned i;
@@ -1622,5 +1623,12 @@ HRESULT CArchiveExtractCallback::SetDirs
       (WriteATime && ATimeDefined) ? &ATime : NULL,
       (WriteMTime && MTimeDefined) ? &MTime : (_arc->MTimeDefined ? &_arc->MTime : NULL));
   }
-  return S_OK;
+
+  for (int i = 0; i != _delayedSymLinks.Size(); ++i)
+    if (!_delayedSymLinks[i].Create())
+      result = E_FAIL;
+
+  _delayedSymLinks.Clear();
+
+  return result;
 }
diff -rup p7zip_15.09.orig/CPP/7zip/UI/Common/ArchiveExtractCallback.h p7zip_15.09/CPP/7zip/UI/Common/ArchiveExtractCallback.h
--- p7zip_15.09.orig/CPP/7zip/UI/Common/ArchiveExtractCallback.h	2015-10-03 11:29:09.000000000 +0100
+++ p7zip_15.09/CPP/7zip/UI/Common/ArchiveExtractCallback.h	2015-12-03 02:22:47.074724204 +0000
@@ -6,6 +6,8 @@
 #include "../../../Common/MyCom.h"
 #include "../../../Common/Wildcard.h"
 
+#include "../../../Windows/FileDir.h"
+
 #include "../../IPassword.h"
 
 #include "../../Common/FileStreams.h"
@@ -237,6 +239,8 @@ class CArchiveExtractCallback:
   bool _saclEnabled;
   #endif
 
+  CObjectVector<NWindows::NFile::NDir::CDelayedSymLink> _delayedSymLinks;
+
   void CreateComplexDirectory(const UStringVector &dirPathParts, FString &fullPath);
   HRESULT GetTime(int index, PROPID propID, FILETIME &filetime, bool &filetimeIsDefined);
   HRESULT GetUnpackSize();
@@ -330,7 +334,7 @@ public:
   }
   #endif
 
-  HRESULT SetDirsTimes();
+  HRESULT SetFinalAttribs();
 };
 
 bool CensorNode_CheckPath(const NWildcard::CCensorNode &node, const CReadArcItem &item);
diff -rup p7zip_15.09.orig/CPP/7zip/UI/Common/Extract.cpp p7zip_15.09/CPP/7zip/UI/Common/Extract.cpp
--- p7zip_15.09.orig/CPP/7zip/UI/Common/Extract.cpp	2015-09-07 20:47:32.000000000 +0100
+++ p7zip_15.09/CPP/7zip/UI/Common/Extract.cpp	2015-12-03 02:22:47.075724215 +0000
@@ -207,7 +207,7 @@ static HRESULT DecompressArchive(
   else
     result = archive->Extract(&realIndices.Front(), realIndices.Size(), testMode, ecs);
   if (result == S_OK && !options.StdInMode)
-    result = ecs->SetDirsTimes();
+    result = ecs->SetFinalAttribs();
   return callback->ExtractResult(result);
 }
 
diff -rup p7zip_15.09.orig/CPP/Windows/FileDir.cpp p7zip_15.09/CPP/Windows/FileDir.cpp
--- p7zip_15.09.orig/CPP/Windows/FileDir.cpp	2015-10-10 13:37:41.000000000 +0100
+++ p7zip_15.09/CPP/Windows/FileDir.cpp	2015-12-03 02:22:47.075724215 +0000
@@ -347,7 +347,8 @@ static int convert_to_symlink(const char
   return -1;
 }
 
-bool SetFileAttrib(CFSTR fileName, DWORD fileAttributes)
+bool SetFileAttrib(CFSTR fileName, DWORD fileAttributes,
+		   CObjectVector<CDelayedSymLink> *delayedSymLinks)
 {
   if (!fileName) {
     SetLastError(ERROR_PATH_NOT_FOUND);
@@ -379,7 +380,9 @@ bool SetFileAttrib(CFSTR fileName, DWORD
      stat_info.st_mode = fileAttributes >> 16;
 #ifdef ENV_HAVE_LSTAT
      if (S_ISLNK(stat_info.st_mode)) {
-        if ( convert_to_symlink(name) != 0) {
+        if (delayedSymLinks)
+          delayedSymLinks->Add(CDelayedSymLink(name));
+        else if ( convert_to_symlink(name) != 0) {
           TRACEN((printf("SetFileAttrib(%s,%d) : false-3\n",(const char *)name,fileAttributes)))
           return false;
         }
@@ -814,6 +817,43 @@ bool CTempDir::Remove()
   return !_mustBeDeleted;
 }
 
+#ifdef ENV_UNIX
+
+CDelayedSymLink::CDelayedSymLink(const char * source)
+  : _source(source)
+{
+  struct stat st;
+
+  if (lstat(_source, &st) == 0) {
+    _dev = st.st_dev;
+    _ino = st.st_ino;
+  } else {
+    _dev = 0;
+  }
+}
+
+bool CDelayedSymLink::Create()
+{
+  struct stat st;
+
+  if (_dev == 0) {
+    errno = EPERM;
+    return false;
+  }
+  if (lstat(_source, &st) != 0)
+    return false;
+  if (_dev != st.st_dev || _ino != st.st_ino) {
+    // Placeholder file has been overwritten or moved by another
+    // symbolic link creation
+    errno = EPERM;
+    return false;
+  }
+
+  return convert_to_symlink(_source) == 0;
+}
+
+#endif // ENV_UNIX
+
 }}}
 
 #ifndef _SFX
diff -rup p7zip_15.09.orig/CPP/Windows/FileDir.h p7zip_15.09/CPP/Windows/FileDir.h
--- p7zip_15.09.orig/CPP/Windows/FileDir.h	2015-06-19 11:52:06.000000000 +0100
+++ p7zip_15.09/CPP/Windows/FileDir.h	2015-12-03 02:22:47.075724215 +0000
@@ -4,6 +4,8 @@
 #define __WINDOWS_FILE_DIR_H
 
 #include "../Common/MyString.h"
+#include "../Common/MyVector.h"
+#include <sys/types.h>
 
 #include "FileIO.h"
 
@@ -11,11 +12,14 @@ namespace NWindows {
 namespace NFile {
 namespace NDir {
 
+class CDelayedSymLink;
+
 bool GetWindowsDir(FString &path);
 bool GetSystemDir(FString &path);
 
 bool SetDirTime(CFSTR path, const FILETIME *cTime, const FILETIME *aTime, const FILETIME *mTime);
-bool SetFileAttrib(CFSTR path, DWORD attrib);
+bool SetFileAttrib(CFSTR path, DWORD attrib,
+		   CObjectVector<CDelayedSymLink> *delayedSymLinks = 0);
 bool MyMoveFile(CFSTR existFileName, CFSTR newFileName);
 
 #ifndef UNDER_CE
@@ -76,6 +80,31 @@ public:
   bool Remove();
 };
 
+// Symbolic links must be created last so that they can't be used to
+// create or overwrite files above the extraction directory.
+class CDelayedSymLink
+{
+#ifdef ENV_UNIX
+  // Where the symlink should be created.  The target is specified in
+  // the placeholder file.
+  AString _source;
+
+  // Device and inode of the placeholder file.  Before creating the
+  // symlink, we must check that these haven't been changed by creation
+  // of another symlink.
+  dev_t _dev;
+  ino_t _ino;
+
+public:
+  explicit CDelayedSymLink(const char * source);
+  bool Create();
+#else // !ENV_UNIX
+public:
+  CDelayedSymLink(const char * source) {}
+  bool Create() { return true; }
+#endif // ENV_UNIX
+};
+
 #if !defined(UNDER_CE)
 class CCurrentDirRestorer
 {
