Initial revision
diff --git a/uidswap.c b/uidswap.c
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+++ b/uidswap.c
@@ -0,0 +1,95 @@
+/*
+
+uidswap.c
+
+Author: Tatu Ylonen <ylo@cs.hut.fi>
+
+Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
+ All rights reserved
+
+Created: Sat Sep 9 01:56:14 1995 ylo
+
+Code for uid-swapping.
+
+*/
+
+#include "includes.h"
+RCSID("$Id: uidswap.c,v 1.1 1999/10/27 03:42:46 damien Exp $");
+
+#include "ssh.h"
+#include "uidswap.h"
+
+/* Note: all these functions must work in all of the following cases:
+
+ 1. euid=0, ruid=0
+ 2. euid=0, ruid!=0
+ 3. euid!=0, ruid!=0
+
+ Additionally, they must work regardless of whether the system has
+ POSIX saved uids or not. */
+
+#ifdef _POSIX_SAVED_IDS
+/* Lets assume that posix saved ids also work with seteuid, even though that
+ is not part of the posix specification. */
+#define SAVED_IDS_WORK_WITH_SETEUID
+#endif /* _POSIX_SAVED_IDS */
+
+/* Saved effective uid. */
+static uid_t saved_euid = 0;
+
+/* Temporarily changes to the given uid. If the effective user id is not
+ root, this does nothing. This call cannot be nested. */
+
+void temporarily_use_uid(uid_t uid)
+{
+#ifdef SAVED_IDS_WORK_WITH_SETEUID
+
+ /* Save the current euid. */
+ saved_euid = geteuid();
+
+ /* Set the effective uid to the given (unprivileged) uid. */
+ if (seteuid(uid) == -1)
+ debug("seteuid %d: %.100s", (int)uid, strerror(errno));
+
+#else /* SAVED_IDS_WORK_WITH_SETUID */
+
+ /* Propagate the privileged uid to all of our uids. */
+ if (setuid(geteuid()) < 0)
+ debug("setuid %d: %.100s", (int)geteuid(), strerror(errno));
+
+ /* Set the effective uid to the given (unprivileged) uid. */
+ if (seteuid(uid) == -1)
+ debug("seteuid %d: %.100s", (int)uid, strerror(errno));
+
+#endif /* SAVED_IDS_WORK_WITH_SETEUID */
+
+}
+
+/* Restores to the original uid. */
+
+void restore_uid()
+{
+#ifdef SAVED_IDS_WORK_WITH_SETEUID
+
+ /* Set the effective uid back to the saved uid. */
+ if (seteuid(saved_euid) < 0)
+ debug("seteuid %d: %.100s", (int)saved_euid, strerror(errno));
+
+#else /* SAVED_IDS_WORK_WITH_SETEUID */
+
+ /* We are unable to restore the real uid to its unprivileged value. */
+ /* Propagate the real uid (usually more privileged) to effective uid
+ as well. */
+ setuid(getuid());
+
+#endif /* SAVED_IDS_WORK_WITH_SETEUID */
+}
+
+/* Permanently sets all uids to the given uid. This cannot be called while
+ temporarily_use_uid is effective. */
+
+void permanently_set_uid(uid_t uid)
+{
+ if (setuid(uid) < 0)
+ debug("setuid %d: %.100s", (int)uid, strerror(errno));
+}