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-rw-r--r--apt-pkg/contrib/fileutl.cc85
-rw-r--r--apt-pkg/contrib/fileutl.h12
2 files changed, 92 insertions, 5 deletions
diff --git a/apt-pkg/contrib/fileutl.cc b/apt-pkg/contrib/fileutl.cc
index 6b8f04dea..e81f32a52 100644
--- a/apt-pkg/contrib/fileutl.cc
+++ b/apt-pkg/contrib/fileutl.cc
@@ -48,6 +48,7 @@
#include <errno.h>
#include <glob.h>
#include <pwd.h>
+#include <grp.h>
#include <set>
#include <algorithm>
@@ -64,6 +65,10 @@
#include <endian.h>
#include <stdint.h>
+#if __gnu_linux__
+#include <sys/prctl.h>
+#endif
+
#include <apti18n.h>
/*}}}*/
@@ -2170,17 +2175,89 @@ bool Popen(const char* Args[], FileFd &Fd, pid_t &Child, FileFd::OpenMode Mode)
bool DropPrivs()
{
- if (getuid() != 0)
+ // uid will be 0 in the end, but gid might be different anyway
+ uid_t old_uid = getuid();
+ gid_t old_gid = getgid();
+
+ if (old_uid != 0)
+ return true;
+ if(_config->FindB("Debug::NoDropPrivs", false) == true)
return true;
- const std::string nobody = _config->Find("APT::User::Nobody", "nobody");
- struct passwd *pw = getpwnam(nobody.c_str());
+ const std::string toUser = _config->Find("APT::Sandbox::User", "_apt");
+ struct passwd *pw = getpwnam(toUser.c_str());
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());
+
+#if __gnu_linux__
+ // see prctl(2), needs linux3.5
+ int ret = prctl(PR_SET_NO_NEW_PRIVS, 1, 0,0, 0);
+ if(ret < 0)
+ _error->Warning("PR_SET_NO_NEW_PRIVS failed with %i", ret);
+#endif
+ // Do not change the order here, it might break things
+ if (setgroups(1, &pw->pw_gid))
+ return _error->Errno("setgroups", "Failed to setgroups");
+
+ 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 (setuid(pw->pw_uid) != 0)
return _error->Errno("setuid", "Failed to setuid");
+ // the seteuid() is probably uneeded (at least thats what the linux
+ // man-page says about setuid(2)) but we cargo culted it anyway
+ if (seteuid(pw->pw_uid) != 0)
+ return _error->Errno("seteuid", "Failed to seteuid");
+
+ // Verify that the user has only a single group, and the correct one
+ gid_t groups[1];
+ if (getgroups(1, groups) != 1)
+ return _error->Errno("getgroups", "Could not get new groups");
+ if (groups[0] != pw->pw_gid)
+ return _error->Error("Could not switch group");
+
+ // 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
+
+ // 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;
}
diff --git a/apt-pkg/contrib/fileutl.h b/apt-pkg/contrib/fileutl.h
index a8e255b86..9dd29eb9e 100644
--- a/apt-pkg/contrib/fileutl.h
+++ b/apt-pkg/contrib/fileutl.h
@@ -199,7 +199,17 @@ bool ExecWait(pid_t Pid,const char *Name,bool Reap = false);
// check if the given file starts with a PGP cleartext signature
bool StartsWithGPGClearTextSignature(std::string const &FileName);
-// process releated
+/**
+ * \brief Drop privileges
+ *
+ * Drop the privileges to the user _apt (or the one specified in
+ * APT::Sandbox::User). This does not set the supplementary group
+ * ids up correctly, it only uses the default group. Also prevent
+ * the process from gaining any new privileges afterwards, at least
+ * on Linux.
+ *
+ * \return true on success, false on failure with _error set
+ */
bool DropPrivs();
// File string manipulators