Revert "Revert "appease adequate with some weak symbols for -private""

[apt.git] / apt-pkg / contrib / fileutl.cc

diff --git a/apt-pkg/contrib/fileutl.cc b/apt-pkg/contrib/fileutl.cc
index 6b8f04dea1519f5206f6385f551dc92cf0764d81..014f0ee51659953d3d2b1a604acc2462c6fb76ed 100644 (file)
--- a/apt-pkg/contrib/fileutl.cc
+++ b/apt-pkg/contrib/fileutl.cc
@@ -48,9 +48,11 @@
 #include <errno.h>
 #include <glob.h>
 #include <pwd.h>
 #include <errno.h>
 #include <glob.h>
 #include <pwd.h>

+#include <grp.h>

 
 #include <set>
 #include <algorithm>
 
 #include <set>
 #include <algorithm>

+#include <memory>

 
 #ifdef HAVE_ZLIB
        #include <zlib.h>
 
 #ifdef HAVE_ZLIB
        #include <zlib.h>


@@ -64,6 +66,10 @@
 #include <endian.h>
 #include <stdint.h>
 
 #include <endian.h>
 #include <stdint.h>
 

+#if __gnu_linux__
+#include <sys/prctl.h>
+#endif
+

 #include <apti18n.h>
                                                                        /*}}}*/
 
 #include <apti18n.h>
                                                                        /*}}}*/
 


@@ -152,24 +158,33 @@ bool CopyFile(FileFd &From,FileFd &To)
    if (From.IsOpen() == false || To.IsOpen() == false ||
         From.Failed() == true || To.Failed() == true)
       return false;
    if (From.IsOpen() == false || To.IsOpen() == false ||
         From.Failed() == true || To.Failed() == true)
       return false;

-   
+

    // Buffered copy between fds
    // Buffered copy between fds

-   SPtrArray<unsigned char> Buf = new unsigned char[64000];
-   unsigned long long Size = From.Size();
-   while (Size != 0)
-   {
-      unsigned long long ToRead = Size;
-      if (Size > 64000)
-        ToRead = 64000;
-      
-      if (From.Read(Buf,ToRead) == false || 
-         To.Write(Buf,ToRead) == false)
+   std::unique_ptr<unsigned char[]> Buf(new unsigned char[64000]);
+   constexpr unsigned long long BufSize = sizeof(Buf.get())/sizeof(Buf.get()[0]);
+   unsigned long long ToRead = 0;
+   do {
+      if (From.Read(Buf.get(),BufSize, &ToRead) == false ||
+         To.Write(Buf.get(),ToRead) == false)

         return false;
         return false;

-      
-      Size -= ToRead;
-   }
+   } while (ToRead != 0);

 
 

-   return true;   
+   return true;
+}
+                                                                       /*}}}*/
+bool RemoveFile(char const * const Function, std::string const &FileName)/*{{{*/
+{
+   if (FileName == "/dev/null")
+      return true;
+   errno = 0;
+   if (unlink(FileName.c_str()) != 0)
+   {
+      if (errno == ENOENT)
+        return true;
+
+      return _error->WarningE(Function,_("Problem unlinking the file %s"), FileName.c_str());
+   }
+   return true;

 }
                                                                        /*}}}*/
 // GetLock - Gets a lock file                                          /*{{{*/
 }
                                                                        /*}}}*/
 // GetLock - Gets a lock file                                          /*{{{*/


@@ -665,7 +680,7 @@ string flAbsPath(string File)
    char *p = realpath(File.c_str(), NULL);
    if (p == NULL)
    {
    char *p = realpath(File.c_str(), NULL);
    if (p == NULL)
    {

-      _error->Errno("realpath", "flAbsPath failed");
+      _error->Errno("realpath", "flAbsPath on %s failed", File.c_str());

       return "";
    }
    std::string AbsPath(p);
       return "";
    }
    std::string AbsPath(p);


@@ -795,11 +810,26 @@ pid_t ExecFork(std::set<int> KeepFDs)
       signal(SIGCONT,SIG_DFL);
       signal(SIGTSTP,SIG_DFL);
 
       signal(SIGCONT,SIG_DFL);
       signal(SIGTSTP,SIG_DFL);
 

-      // Close all of our FDs - just in case
-      for (int K = 3; K != sysconf(_SC_OPEN_MAX); K++)
+      DIR *dir = opendir("/proc/self/fd");
+      if (dir != NULL)

       {
       {

-        if(KeepFDs.find(K) == KeepFDs.end())
-           fcntl(K,F_SETFD,FD_CLOEXEC);
+        struct dirent *ent;
+        while ((ent = readdir(dir)))
+        {
+           int fd = atoi(ent->d_name);
+           // If fd > 0, it was a fd number and not . or ..
+           if (fd >= 3 && KeepFDs.find(fd) == KeepFDs.end())
+              fcntl(fd,F_SETFD,FD_CLOEXEC);
+        }
+        closedir(dir);
+      } else {
+        long ScOpenMax = sysconf(_SC_OPEN_MAX);
+        // Close all of our FDs - just in case
+        for (int K = 3; K != ScOpenMax; K++)
+        {
+           if(KeepFDs.find(K) == KeepFDs.end())
+              fcntl(K,F_SETFD,FD_CLOEXEC);
+        }

       }
    }
    
       }
    }
    


@@ -852,11 +882,7 @@ bool ExecWait(pid_t Pid,const char *Name,bool Reap)
    return true;
 }
                                                                        /*}}}*/
    return true;
 }
                                                                        /*}}}*/

-
-
-// StartsWithGPGClearTextSignature - Check if a file is Pgp/GPG clearsigned     /*{{{*/
-// ---------------------------------------------------------------------
-/* */
+// StartsWithGPGClearTextSignature - Check if a file is Pgp/GPG clearsigned    /*{{{*/

 bool StartsWithGPGClearTextSignature(string const &FileName)
 {
    static const char* SIGMSG = "-----BEGIN PGP SIGNED MESSAGE-----\n";
 bool StartsWithGPGClearTextSignature(string const &FileName)
 {
    static const char* SIGMSG = "-----BEGIN PGP SIGNED MESSAGE-----\n";


@@ -872,7 +898,26 @@ bool StartsWithGPGClearTextSignature(string const &FileName)
 
    return true;
 }
 
    return true;
 }

-
+                                                                       /*}}}*/
+// ChangeOwnerAndPermissionOfFile - set file attributes to requested values /*{{{*/
+bool ChangeOwnerAndPermissionOfFile(char const * const requester, char const * const file, char const * const user, char const * const group, mode_t const mode)
+{
+   if (strcmp(file, "/dev/null") == 0)
+      return true;
+   bool Res = true;
+   if (getuid() == 0 && strlen(user) != 0 && strlen(group) != 0) // if we aren't root, we can't chown, so don't try it
+   {
+      // ensure the file is owned by root and has good permissions
+      struct passwd const * const pw = getpwnam(user);
+      struct group const * const gr = getgrnam(group);
+      if (pw != NULL && gr != NULL && chown(file, pw->pw_uid, gr->gr_gid) != 0)
+        Res &= _error->WarningE(requester, "chown to %s:%s of file %s failed", user, group, file);
+   }
+   if (chmod(file, mode) != 0)
+      Res &= _error->WarningE(requester, "chmod 0%o of file %s failed", mode, file);
+   return Res;
+}
+                                                                       /*}}}*/

 
 class FileFdPrivate {                                                  /*{{{*/
        public:
 
 class FileFdPrivate {                                                  /*{{{*/
        public:


@@ -891,7 +936,7 @@ class FileFdPrivate {                                                       /*{{{*/
           bool eof;
           bool compressing;
 
           bool eof;
           bool compressing;
 

-          LZMAFILE() : file(NULL), eof(false), compressing(false) {}
+          LZMAFILE() : file(NULL), eof(false), compressing(false) { buffer[0] = '\0'; }

           ~LZMAFILE() {
              if (compressing == true)
              {
           ~LZMAFILE() {
              if (compressing == true)
              {


@@ -990,6 +1035,25 @@ class FileFdPrivate {                                                     /*{{{*/
        ~FileFdPrivate() { CloseDown(""); }
 };
                                                                        /*}}}*/
        ~FileFdPrivate() { CloseDown(""); }
 };
                                                                        /*}}}*/

+// FileFd Constructors                                                 /*{{{*/
+FileFd::FileFd(std::string FileName,unsigned int const Mode,unsigned long AccessMode) : iFd(-1), Flags(0), d(NULL)
+{
+   Open(FileName,Mode, None, AccessMode);
+}
+FileFd::FileFd(std::string FileName,unsigned int const Mode, CompressMode Compress, unsigned long AccessMode) : iFd(-1), Flags(0), d(NULL)
+{
+   Open(FileName,Mode, Compress, AccessMode);
+}
+FileFd::FileFd() : iFd(-1), Flags(AutoClose), d(NULL) {}
+FileFd::FileFd(int const Fd, unsigned int const Mode, CompressMode Compress) : iFd(-1), Flags(0), d(NULL)
+{
+   OpenDescriptor(Fd, Mode, Compress);
+}
+FileFd::FileFd(int const Fd, bool const AutoClose) : iFd(-1), Flags(0), d(NULL)
+{
+   OpenDescriptor(Fd, ReadWrite, None, AutoClose);
+}
+                                                                       /*}}}*/

 // FileFd::Open - Open a file                                          /*{{{*/
 // ---------------------------------------------------------------------
 /* The most commonly used open mode combinations are given with Mode */
 // FileFd::Open - Open a file                                          /*{{{*/
 // ---------------------------------------------------------------------
 /* The most commonly used open mode combinations are given with Mode */


@@ -1075,24 +1139,28 @@ bool FileFd::Open(string FileName,unsigned int const Mode,APT::Configuration::Co
    if ((Mode & ReadWrite) == 0)
       return FileFdError("No openmode provided in FileFd::Open for %s", FileName.c_str());
 
    if ((Mode & ReadWrite) == 0)
       return FileFdError("No openmode provided in FileFd::Open for %s", FileName.c_str());
 

-   if ((Mode & Atomic) == Atomic)
+   unsigned int OpenMode = Mode;
+   if (FileName == "/dev/null")
+      OpenMode = OpenMode & ~(Atomic | Exclusive | Create | Empty);
+
+   if ((OpenMode & Atomic) == Atomic)

    {
       Flags |= Replace;
    }
    {
       Flags |= Replace;
    }

-   else if ((Mode & (Exclusive | Create)) == (Exclusive | Create))
+   else if ((OpenMode & (Exclusive | Create)) == (Exclusive | Create))

    {
       // for atomic, this will be done by rename in Close()
    {
       // for atomic, this will be done by rename in Close()

-      unlink(FileName.c_str());
+      RemoveFile("FileFd::Open", FileName);

    }
    }

-   if ((Mode & Empty) == Empty)
+   if ((OpenMode & Empty) == Empty)

    {
       struct stat Buf;
       if (lstat(FileName.c_str(),&Buf) == 0 && S_ISLNK(Buf.st_mode))
    {
       struct stat Buf;
       if (lstat(FileName.c_str(),&Buf) == 0 && S_ISLNK(Buf.st_mode))

-        unlink(FileName.c_str());
+        RemoveFile("FileFd::Open", FileName);

    }
 
    int fileflags = 0;
    }
 
    int fileflags = 0;

-   #define if_FLAGGED_SET(FLAG, MODE) if ((Mode & FLAG) == FLAG) fileflags |= MODE
+   #define if_FLAGGED_SET(FLAG, MODE) if ((OpenMode & FLAG) == FLAG) fileflags |= MODE

    if_FLAGGED_SET(ReadWrite, O_RDWR);
    else if_FLAGGED_SET(ReadOnly, O_RDONLY);
    else if_FLAGGED_SET(WriteOnly, O_WRONLY);
    if_FLAGGED_SET(ReadWrite, O_RDWR);
    else if_FLAGGED_SET(ReadOnly, O_RDONLY);
    else if_FLAGGED_SET(WriteOnly, O_WRONLY);


@@ -1102,7 +1170,7 @@ bool FileFd::Open(string FileName,unsigned int const Mode,APT::Configuration::Co
    if_FLAGGED_SET(Exclusive, O_EXCL);
    #undef if_FLAGGED_SET
 
    if_FLAGGED_SET(Exclusive, O_EXCL);
    #undef if_FLAGGED_SET
 

-   if ((Mode & Atomic) == Atomic)
+   if ((OpenMode & Atomic) == Atomic)

    {
       char *name = strdup((FileName + ".XXXXXX").c_str());
 
    {
       char *name = strdup((FileName + ".XXXXXX").c_str());
 


@@ -1129,7 +1197,7 @@ bool FileFd::Open(string FileName,unsigned int const Mode,APT::Configuration::Co
       iFd = open(FileName.c_str(), fileflags, AccessMode);
 
    this->FileName = FileName;
       iFd = open(FileName.c_str(), fileflags, AccessMode);
 
    this->FileName = FileName;

-   if (iFd == -1 || OpenInternDescriptor(Mode, compressor) == false)
+   if (iFd == -1 || OpenInternDescriptor(OpenMode, compressor) == false)

    {
       if (iFd != -1)
       {
    {
       if (iFd != -1)
       {


@@ -1520,7 +1588,7 @@ bool FileFd::Read(void *To,unsigned long long Size,unsigned long long *Actual)
            int err;
            char const * const errmsg = BZ2_bzerror(d->bz2, &err);
            if (err != BZ_IO_ERROR)
            int err;
            char const * const errmsg = BZ2_bzerror(d->bz2, &err);
            if (err != BZ_IO_ERROR)

-              return FileFdError("BZ2_bzread: %s (%d: %s)", _("Read error"), err, errmsg);
+              return FileFdError("BZ2_bzread: %s %s (%d: %s)", FileName.c_str(), _("Read error"), err, errmsg);

         }
 #endif
 #ifdef HAVE_LZMA
         }
 #endif
 #ifdef HAVE_LZMA


@@ -1951,12 +2019,13 @@ bool FileFd::Close()
    {
       if ((Flags & Compressed) != Compressed && iFd > 0 && close(iFd) != 0)
         Res &= _error->Errno("close",_("Problem closing the file %s"), FileName.c_str());
    {
       if ((Flags & Compressed) != Compressed && iFd > 0 && close(iFd) != 0)
         Res &= _error->Errno("close",_("Problem closing the file %s"), FileName.c_str());

-      if (d != NULL)
-      {
-        Res &= d->CloseDown(FileName);
-        delete d;
-        d = NULL;
-      }
+   }
+
+   if (d != NULL)
+   {
+      Res &= d->CloseDown(FileName);
+      delete d;
+      d = NULL;

    }
 
    if ((Flags & Replace) == Replace) {
    }
 
    if ((Flags & Replace) == Replace) {


@@ -1971,8 +2040,7 @@ bool FileFd::Close()
 
    if ((Flags & Fail) == Fail && (Flags & DelOnFail) == DelOnFail &&
        FileName.empty() == false)
 
    if ((Flags & Fail) == Fail && (Flags & DelOnFail) == DelOnFail &&
        FileName.empty() == false)

-      if (unlink(FileName.c_str()) != 0)
-        Res &= _error->WarningE("unlnk",_("Problem unlinking the file %s"), FileName.c_str());
+      Res &= RemoveFile("FileFd::Close", FileName);

 
    if (Res == false)
       Flags |= Fail;
 
    if (Res == false)
       Flags |= Fail;


@@ -2022,7 +2090,7 @@ bool FileFd::FileFdError(const char *Description,...) {
 }
                                                                        /*}}}*/
 
 }
                                                                        /*}}}*/
 

-APT_DEPRECATED gzFile FileFd::gzFd() {
+gzFile FileFd::gzFd() {

 #ifdef HAVE_ZLIB
    return d->gz;
 #else
 #ifdef HAVE_ZLIB
    return d->gz;
 #else


@@ -2030,10 +2098,7 @@ APT_DEPRECATED gzFile FileFd::gzFd() {
 #endif
 }
 
 #endif
 }
 

-
-// Glob - wrapper around "glob()"                                      /*{{{*/
-// ---------------------------------------------------------------------
-/* */
+// Glob - wrapper around "glob()"                                      /*{{{*/

 std::vector<std::string> Glob(std::string const &pattern, int flags)
 {
    std::vector<std::string> result;
 std::vector<std::string> Glob(std::string const &pattern, int flags)
 {
    std::vector<std::string> result;


@@ -2059,8 +2124,7 @@ std::vector<std::string> Glob(std::string const &pattern, int flags)
    return result;
 }
                                                                        /*}}}*/
    return result;
 }
                                                                        /*}}}*/

-
-std::string GetTempDir()
+std::string GetTempDir()                                               /*{{{*/

 {
    const char *tmpdir = getenv("TMPDIR");
 
 {
    const char *tmpdir = getenv("TMPDIR");
 


@@ -2069,51 +2133,79 @@ std::string GetTempDir()
       tmpdir = P_tmpdir;
 #endif
 
       tmpdir = P_tmpdir;
 #endif
 

-   // check that tmpdir is set and exists

    struct stat st;
    struct stat st;

-   if (!tmpdir || strlen(tmpdir) == 0 || stat(tmpdir, &st) != 0)
+   if (!tmpdir || strlen(tmpdir) == 0 || // tmpdir is set
+        stat(tmpdir, &st) != 0 || (st.st_mode & S_IFDIR) == 0) // exists and is directory
+      tmpdir = "/tmp";
+   else if (geteuid() != 0 && // root can do everything anyway
+        faccessat(-1, tmpdir, R_OK | W_OK | X_OK, AT_EACCESS | AT_SYMLINK_NOFOLLOW) != 0) // current user has rwx access to directory

       tmpdir = "/tmp";
 
    return string(tmpdir);
 }
       tmpdir = "/tmp";
 
    return string(tmpdir);
 }

+std::string GetTempDir(std::string const &User)
+{
+   // no need/possibility to drop privs
+   if(getuid() != 0 || User.empty() || User == "root")
+      return GetTempDir();
+
+   struct passwd const * const pw = getpwnam(User.c_str());
+   if (pw == NULL)
+      return GetTempDir();
+
+   gid_t const old_euid = geteuid();
+   gid_t const old_egid = getegid();
+   if (setegid(pw->pw_gid) != 0)
+      _error->Errno("setegid", "setegid %u failed", pw->pw_gid);
+   if (seteuid(pw->pw_uid) != 0)
+      _error->Errno("seteuid", "seteuid %u failed", pw->pw_uid);
+
+   std::string const tmp = GetTempDir();
+
+   if (seteuid(old_euid) != 0)
+      _error->Errno("seteuid", "seteuid %u failed", old_euid);
+   if (setegid(old_egid) != 0)
+      _error->Errno("setegid", "setegid %u failed", old_egid);

 
 

-FileFd* GetTempFile(std::string const &Prefix, bool ImmediateUnlink)
+   return tmp;
+}
+                                                                       /*}}}*/
+FileFd* GetTempFile(std::string const &Prefix, bool ImmediateUnlink, FileFd * const TmpFd)     /*{{{*/

 {
    char fn[512];
 {
    char fn[512];

-   FileFd *Fd = new FileFd();
+   FileFd * const Fd = TmpFd == NULL ? new FileFd() : TmpFd;

 
 

-   std::string tempdir = GetTempDir();
-   snprintf(fn, sizeof(fn), "%s/%s.XXXXXX", 
+   std::string const tempdir = GetTempDir();
+   snprintf(fn, sizeof(fn), "%s/%s.XXXXXX",

             tempdir.c_str(), Prefix.c_str());
             tempdir.c_str(), Prefix.c_str());

-   int fd = mkstemp(fn);
+   int const fd = mkstemp(fn);

    if(ImmediateUnlink)
       unlink(fn);
    if(ImmediateUnlink)
       unlink(fn);

-   if (fd < 0) 
+   if (fd < 0)

    {
       _error->Errno("GetTempFile",_("Unable to mkstemp %s"), fn);
       return NULL;
    }
    {
       _error->Errno("GetTempFile",_("Unable to mkstemp %s"), fn);
       return NULL;
    }

-   if (!Fd->OpenDescriptor(fd, FileFd::WriteOnly, FileFd::None, true))
+   if (!Fd->OpenDescriptor(fd, FileFd::ReadWrite, FileFd::None, true))

    {
       _error->Errno("GetTempFile",_("Unable to write to %s"),fn);
       return NULL;
    }
    {
       _error->Errno("GetTempFile",_("Unable to write to %s"),fn);
       return NULL;
    }

-

    return Fd;
 }
    return Fd;
 }

-
-bool Rename(std::string From, std::string To)
+                                                                       /*}}}*/
+bool Rename(std::string From, std::string To)                          /*{{{*/

 {
    if (rename(From.c_str(),To.c_str()) != 0)
    {
       _error->Error(_("rename failed, %s (%s -> %s)."),strerror(errno),
                     From.c_str(),To.c_str());
       return false;
 {
    if (rename(From.c_str(),To.c_str()) != 0)
    {
       _error->Error(_("rename failed, %s (%s -> %s)."),strerror(errno),
                     From.c_str(),To.c_str());
       return false;

-   }   
+   }

    return true;
 }
    return true;
 }

-
-bool Popen(const char* Args[], FileFd &Fd, pid_t &Child, FileFd::OpenMode Mode)
+                                                                       /*}}}*/
+bool Popen(const char* Args[], FileFd &Fd, pid_t &Child, FileFd::OpenMode Mode)/*{{{*/

 {
    int fd;
    if (Mode != FileFd::ReadOnly && Mode != FileFd::WriteOnly)
 {
    int fd;
    if (Mode != FileFd::ReadOnly && Mode != FileFd::WriteOnly)


@@ -2121,10 +2213,8 @@ bool Popen(const char* Args[], FileFd &Fd, pid_t &Child, FileFd::OpenMode Mode)
 
    int Pipe[2] = {-1, -1};
    if(pipe(Pipe) != 0)
 
    int Pipe[2] = {-1, -1};
    if(pipe(Pipe) != 0)

-   {

       return _error->Errno("pipe", _("Failed to create subprocess IPC"));
       return _error->Errno("pipe", _("Failed to create subprocess IPC"));

-      return NULL;
-   }
+

    std::set<int> keep_fds;
    keep_fds.insert(Pipe[0]);
    keep_fds.insert(Pipe[1]);
    std::set<int> keep_fds;
    keep_fds.insert(Pipe[0]);
    keep_fds.insert(Pipe[1]);


@@ -2158,29 +2248,149 @@ bool Popen(const char* Args[], FileFd &Fd, pid_t &Child, FileFd::OpenMode Mode)
    {
       close(Pipe[1]);
       fd = Pipe[0];
    {
       close(Pipe[1]);
       fd = Pipe[0];

-   } else if(Mode == FileFd::WriteOnly)
+   }
+   else if(Mode == FileFd::WriteOnly)

    {
       close(Pipe[0]);
       fd = Pipe[1];
    }
    {
       close(Pipe[0]);
       fd = Pipe[1];
    }

+   else
+      return _error->Error("Popen supports ReadOnly (x)or WriteOnly mode only");

    Fd.OpenDescriptor(fd, Mode, FileFd::None, true);
 
    return true;
 }
    Fd.OpenDescriptor(fd, Mode, FileFd::None, true);
 
    return true;
 }

-
-bool DropPrivs()
+                                                                       /*}}}*/
+bool DropPrivileges()                                                  /*{{{*/

 {
 {

-   if (getuid() != 0)
+   if(_config->FindB("Debug::NoDropPrivs", false) == true)

       return true;
 
       return true;
 

-   const std::string nobody = _config->Find("APT::User::Nobody", "nobody");
-   struct passwd *pw = getpwnam(nobody.c_str());
+#if __gnu_linux__
+#if defined(PR_SET_NO_NEW_PRIVS) && ( PR_SET_NO_NEW_PRIVS != 38 )
+#error "PR_SET_NO_NEW_PRIVS is defined, but with a different value than expected!"
+#endif
+   // see prctl(2), needs linux3.5 at runtime - magic constant to avoid it at buildtime
+   int ret = prctl(38, 1, 0, 0, 0);
+   // ignore EINVAL - kernel is too old to understand the option
+   if(ret < 0 && errno != EINVAL)
+      _error->Warning("PR_SET_NO_NEW_PRIVS failed with %i", ret);
+#endif
+
+   // empty setting disables privilege dropping - this also ensures
+   // backward compatibility, see bug #764506
+   const std::string toUser = _config->Find("APT::Sandbox::User");
+   if (toUser.empty() || toUser == "root")
+      return true;
+
+   // a lot can go wrong trying to drop privileges completely,
+   // so ideally we would like to verify that we have done it –
+   // but the verify asks for too much in case of fakeroot (and alike)
+   // [Specific checks can be overridden with dedicated options]
+   bool const VerifySandboxing = _config->FindB("APT::Sandbox::Verify", false);
+
+   // uid will be 0 in the end, but gid might be different anyway
+   uid_t const old_uid = getuid();
+   gid_t const old_gid = getgid();
+
+   if (old_uid != 0)
+      return true;
+
+   struct passwd *pw = getpwnam(toUser.c_str());

    if (pw == NULL)
    if (pw == NULL)

-      return _error->Warning("No user %s, can not drop rights", nobody.c_str());
+      return _error->Error("No user %s, can not drop rights", toUser.c_str());
+
+   // Do not change the order here, it might break things
+   // Get rid of all our supplementary groups first
+   if (setgroups(1, &pw->pw_gid))
+      return _error->Errno("setgroups", "Failed to setgroups");
+
+   // Now change the group ids to the new user
+#ifdef HAVE_SETRESGID
+   if (setresgid(pw->pw_gid, pw->pw_gid, pw->pw_gid) != 0)
+      return _error->Errno("setresgid", "Failed to set new group ids");
+#else
+   if (setegid(pw->pw_gid) != 0)
+      return _error->Errno("setegid", "Failed to setegid");
+

    if (setgid(pw->pw_gid) != 0)
       return _error->Errno("setgid", "Failed to setgid");
    if (setgid(pw->pw_gid) != 0)
       return _error->Errno("setgid", "Failed to setgid");

+#endif
+
+   // Change the user ids to the new user
+#ifdef HAVE_SETRESUID
+   if (setresuid(pw->pw_uid, pw->pw_uid, pw->pw_uid) != 0)
+      return _error->Errno("setresuid", "Failed to set new user ids");
+#else

    if (setuid(pw->pw_uid) != 0)
       return _error->Errno("setuid", "Failed to setuid");
    if (setuid(pw->pw_uid) != 0)
       return _error->Errno("setuid", "Failed to setuid");

+   if (seteuid(pw->pw_uid) != 0)
+      return _error->Errno("seteuid", "Failed to seteuid");
+#endif
+
+   // disabled by default as fakeroot doesn't implement getgroups currently (#806521)
+   if (VerifySandboxing == true || _config->FindB("APT::Sandbox::Verify::Groups", false) == true)
+   {
+      // Verify that the user isn't still in any supplementary groups
+      long const ngroups_max = sysconf(_SC_NGROUPS_MAX);
+      std::unique_ptr<gid_t[]> gidlist(new gid_t[ngroups_max]);
+      if (unlikely(gidlist == NULL))
+        return _error->Error("Allocation of a list of size %lu for getgroups failed", ngroups_max);
+      ssize_t gidlist_nr;
+      if ((gidlist_nr = getgroups(ngroups_max, gidlist.get())) < 0)
+        return _error->Errno("getgroups", "Could not get new groups (%lu)", ngroups_max);
+      for (ssize_t i = 0; i < gidlist_nr; ++i)
+        if (gidlist[i] != pw->pw_gid)
+           return _error->Error("Could not switch group, user %s is still in group %d", toUser.c_str(), gidlist[i]);
+   }
+
+   // enabled by default as all fakeroot-lookalikes should fake that accordingly
+   if (VerifySandboxing == true || _config->FindB("APT::Sandbox::Verify::IDs", true) == true)
+   {
+      // Verify that gid, egid, uid, and euid changed
+      if (getgid() != pw->pw_gid)
+        return _error->Error("Could not switch group");
+      if (getegid() != pw->pw_gid)
+        return _error->Error("Could not switch effective group");
+      if (getuid() != pw->pw_uid)
+        return _error->Error("Could not switch user");
+      if (geteuid() != pw->pw_uid)
+        return _error->Error("Could not switch effective user");
+
+#ifdef HAVE_GETRESUID
+      // verify that the saved set-user-id was changed as well
+      uid_t ruid = 0;
+      uid_t euid = 0;
+      uid_t suid = 0;
+      if (getresuid(&ruid, &euid, &suid))
+        return _error->Errno("getresuid", "Could not get saved set-user-ID");
+      if (suid != pw->pw_uid)
+        return _error->Error("Could not switch saved set-user-ID");
+#endif
+
+#ifdef HAVE_GETRESGID
+      // verify that the saved set-group-id was changed as well
+      gid_t rgid = 0;
+      gid_t egid = 0;
+      gid_t sgid = 0;
+      if (getresgid(&rgid, &egid, &sgid))
+        return _error->Errno("getresuid", "Could not get saved set-group-ID");
+      if (sgid != pw->pw_gid)
+        return _error->Error("Could not switch saved set-group-ID");
+#endif
+   }
+
+   // disabled as fakeroot doesn't forbid (by design) (re)gaining root from unprivileged
+   if (VerifySandboxing == true || _config->FindB("APT::Sandbox::Verify::Regain", false) == true)
+   {
+      // Check that uid and gid changes do not work anymore
+      if (pw->pw_gid != old_gid && (setgid(old_gid) != -1 || setegid(old_gid) != -1))
+        return _error->Error("Could restore a gid to root, privilege dropping did not work");
+
+      if (pw->pw_uid != old_uid && (setuid(old_uid) != -1 || seteuid(old_uid) != -1))
+        return _error->Error("Could restore a uid to root, privilege dropping did not work");
+   }

 
    return true;
 }
 
    return true;
 }

+                                                                       /*}}}*/