- (djm) Implement paranoid priv dropping checks, based on:

   "SetUID demystified" - Hao Chen, David Wagner and Drew Dean
   Proceedings of USENIX Security Symposium 2002

1 files changed, 47 insertions, 0 deletions

diff --git a/uidswap.c b/uidswap.c
index db6253259..04c269b0a 100644
--- a/uidswap.c
+++ b/uidswap.c
@@ -143,16 +143,63 @@ restore_uid(void)
 void
 permanently_set_uid(struct passwd *pw)
 {
+        uid_t old_uid = getuid();
+        gid_t old_gid = getgid();
+
         if (temporarily_use_uid_effective)
                 fatal("permanently_set_uid: temporarily_use_uid effective");
         debug("permanently_set_uid: %u/%u", (u_int)pw->pw_uid,
             (u_int)pw->pw_gid);
+
+#if defined(HAVE_SETRESGID)
+        if (setresgid(pw->pw_gid, pw->pw_gid, pw->pw_gid) < 0)
+                fatal("setresgid %u: %.100s", (u_int)pw->pw_gid, strerror(errno));
+#elif defined(HAVE_SETREGID)
+        if (setregid(pw->pw_gid, pw->pw_gid) < 0)
+                fatal("setregid %u: %.100s", (u_int)pw->pw_gid, strerror(errno));
+#else
         if (setegid(pw->pw_gid) < 0)
                 fatal("setegid %u: %.100s", (u_int)pw->pw_gid, strerror(errno));
         if (setgid(pw->pw_gid) < 0)
                 fatal("setgid %u: %.100s", (u_int)pw->pw_gid, strerror(errno));
+#endif
+
+#if defined(HAVE_SETRESUID)
+        if (setresuid(pw->pw_uid, pw->pw_uid, pw->pw_uid) < 0)
+                fatal("setresuid %u: %.100s", (u_int)pw->pw_uid, strerror(errno));
+#elif defined(HAVE_SETRESUID)
+        if (setresuid(pw->pw_uid, pw->pw_uid, pw->pw_uid) < 0)
+                fatal("setresuid %u: %.100s", (u_int)pw->pw_uid, strerror(errno));
+#else
+# ifndef SETEUID_BREAKS_SETUID
         if (seteuid(pw->pw_uid) < 0)
                 fatal("seteuid %u: %.100s", (u_int)pw->pw_uid, strerror(errno));
+# endif
         if (setuid(pw->pw_uid) < 0)
                 fatal("setuid %u: %.100s", (u_int)pw->pw_uid, strerror(errno));
+#endif
+
+        /* Try restoration of GID if changed (test clearing of saved gid) */
+        if (old_gid != pw->pw_gid && 
+            (setgid(old_gid) != -1 || setegid(old_gid) != -1))
+                fatal("%s: was able to restore old [e]gid");
+
+        /* Verify GID drop was successful */
+        if (getgid() != pw->pw_gid || getegid() != pw->pw_gid) {
+                fatal("%s: egid incorrect gid:%u egid:%u (should be %u)", 
+                    __func__, (u_int)getgid(), (u_int)getegid(), 
+                    (u_int)pw->pw_gid);
+        }
+
+        /* Try restoration of UID if changed (test clearing of saved uid) */
+        if (old_uid != pw->pw_uid && 
+            (setuid(old_uid) != -1 || seteuid(old_uid) != -1))
+                fatal("%s: was able to restore old [e]uid");
+
+        /* Verify UID drop was successful */
+        if (getuid() != pw->pw_uid || geteuid() != pw->pw_uid) {
+                fatal("%s: euid incorrect uid:%u euid:%u (should be %u)", 
+                    __func__, (u_int)getuid(), (u_int)geteuid(), 
+                    (u_int)pw->pw_uid);
+        }
 }