Don't call setgroups if we have zero groups; there's no guarantee that it

won't try to deref the pointer.  Based on a patch from mail at quitesimple.org,
ok djm deraadt

diff --git a/usr.bin/ssh/uidswap.c b/usr.bin/ssh/uidswap.c
index e9dee64..ed09f5a 100644 (file)
--- a/usr.bin/ssh/uidswap.c
+++ b/usr.bin/ssh/uidswap.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: uidswap.c,v 1.37 2015/01/16 06:40:12 deraadt Exp $ */
+/* $OpenBSD: uidswap.c,v 1.38 2015/06/22 12:29:57 dtucker Exp $ */
 /*
  * Author: Tatu Ylonen <ylo@cs.hut.fi>
  * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
@@ -76,7 +76,7 @@ temporarily_use_uid(struct passwd *pw)
                        fatal("getgroups: %.100s", strerror(errno));
        }
        /* Set the effective uid to the given (unprivileged) uid. */
-       if (setgroups(user_groupslen, user_groups) < 0)
+       if (user_groupslen > 0 && setgroups(user_groupslen, user_groups) < 0)
                fatal("setgroups: %.100s", strerror(errno));
        if (setegid(pw->pw_gid) < 0)
                fatal("setegid %u: %.100s", (u_int)pw->pw_gid,
@@ -103,7 +103,8 @@ restore_uid(void)
        /* Set the effective uid back to the saved privileged uid. */
        if (seteuid(saved_euid) < 0)
                fatal("seteuid %u: %.100s", (u_int)saved_euid, strerror(errno));
-       if (setgroups(saved_egroupslen, saved_egroups) < 0)
+       if (saved_egroupslen > 0 &&
+           setgroups(saved_egroupslen, saved_egroups) < 0)
                fatal("setgroups: %.100s", strerror(errno));
        if (setegid(saved_egid) < 0)
                fatal("setegid %u: %.100s", (u_int)saved_egid, strerror(errno));