+static bool IsAccessibleBySandboxUser(std::string const &filename, bool const ReadWrite)
+{
+ // you would think this is easily to answer with faccessat, right? Wrong!
+ // It e.g. gets groups wrong, so the only thing which works reliable is trying
+ // to open the file we want to open later on…
+ if (unlikely(filename.empty()))
+ return true;
+
+ if (ReadWrite == false)
+ {
+ errno = 0;
+ // can we read a file? Note that non-existing files are "fine"
+ int const fd = open(filename.c_str(), O_RDONLY | O_CLOEXEC);
+ if (fd == -1 && errno == EACCES)
+ return false;
+ close(fd);
+ return true;
+ }
+ else
+ {
+ // the file might not exist yet and even if it does we will fix permissions,
+ // so important is here just that the directory it is in allows that
+ std::string const dirname = flNotFile(filename);
+ if (unlikely(dirname.empty()))
+ return true;
+
+ char const * const filetag = ".apt-acquire-privs-test.XXXXXX";
+ std::string const tmpfile_tpl = flCombine(dirname, filetag);
+ std::unique_ptr<char, decltype(std::free) *> tmpfile { strdup(tmpfile_tpl.c_str()), std::free };
+ int const fd = mkstemp(tmpfile.get());
+ if (fd == -1 && errno == EACCES)
+ return false;
+ RemoveFile("IsAccessibleBySandboxUser", tmpfile.get());
+ close(fd);
+ return true;
+ }
+}
+static void CheckDropPrivsMustBeDisabled(pkgAcquire const &Fetcher)
+{
+ if(getuid() != 0)
+ return;
+
+ std::string const SandboxUser = _config->Find("APT::Sandbox::User");
+ if (SandboxUser.empty() || SandboxUser == "root")
+ return;
+
+ struct passwd const * const pw = getpwnam(SandboxUser.c_str());
+ if (pw == NULL)
+ {
+ _error->Warning(_("No sandbox user '%s' on the system, can not drop privileges"), SandboxUser.c_str());
+ _config->Set("APT::Sandbox::User", "");
+ return;
+ }
+
+ gid_t const old_euid = geteuid();
+ gid_t const old_egid = getegid();
+
+ long const ngroups_max = sysconf(_SC_NGROUPS_MAX);
+ std::unique_ptr<gid_t[]> old_gidlist(new gid_t[ngroups_max]);
+ if (unlikely(old_gidlist == NULL))
+ return;
+ ssize_t old_gidlist_nr;
+ if ((old_gidlist_nr = getgroups(ngroups_max, old_gidlist.get())) < 0)
+ {
+ _error->FatalE("getgroups", "getgroups %lu failed", ngroups_max);
+ old_gidlist[0] = 0;
+ old_gidlist_nr = 1;
+ }
+ if (setgroups(1, &pw->pw_gid))
+ _error->FatalE("setgroups", "setgroups %u failed", pw->pw_gid);
+
+ if (setegid(pw->pw_gid) != 0)
+ _error->FatalE("setegid", "setegid %u failed", pw->pw_gid);
+ if (seteuid(pw->pw_uid) != 0)
+ _error->FatalE("seteuid", "seteuid %u failed", pw->pw_uid);
+
+ for (pkgAcquire::ItemCIterator I = Fetcher.ItemsBegin();
+ I != Fetcher.ItemsEnd(); ++I)
+ {
+ // no need to drop privileges for a complete file
+ if ((*I)->Complete == true)
+ continue;
+
+ // if destination file is inaccessible all hope is lost for privilege dropping
+ if (IsAccessibleBySandboxUser((*I)->DestFile, true) == false)
+ {
+ _error->WarningE("pkgAcquire::Run", _("Can't drop privileges for downloading as file '%s' couldn't be accessed by user '%s'."),
+ (*I)->DestFile.c_str(), SandboxUser.c_str());
+ _config->Set("APT::Sandbox::User", "");
+ break;
+ }
+
+ // if its the source file (e.g. local sources) we might be lucky
+ // by dropping the dropping only for some methods.
+ URI const source = (*I)->DescURI();
+ if (source.Access == "file" || source.Access == "copy")
+ {
+ std::string const conf = "Binary::" + source.Access + "::APT::Sandbox::User";
+ if (_config->Exists(conf) == true)
+ continue;
+
+ if (IsAccessibleBySandboxUser(source.Path, false) == false)
+ {
+ _error->NoticeE("pkgAcquire::Run", _("Can't drop privileges for downloading as file '%s' couldn't be accessed by user '%s'."),
+ source.Path.c_str(), SandboxUser.c_str());
+ _config->CndSet("Binary::file::APT::Sandbox::User", "root");
+ _config->CndSet("Binary::copy::APT::Sandbox::User", "root");
+ }
+ }
+ }
+
+ if (seteuid(old_euid) != 0)
+ _error->FatalE("seteuid", "seteuid %u failed", old_euid);
+ if (setegid(old_egid) != 0)
+ _error->FatalE("setegid", "setegid %u failed", old_egid);
+ if (setgroups(old_gidlist_nr, old_gidlist.get()))
+ _error->FatalE("setgroups", "setgroups %u failed", 0);
+}
projects / apt.git / blobdiff