Use setfsuid() rather than seteuid() while creating contexts

Signed-off-by: Kevin Coffman <kwc@citi.umich.edu>
As suggested by Olaf Kirch <okir@suse.de>, use setfsuid() rather than
seteuid() when creating a gss context.  This prevents users from using
credentials that do not belong to them, while also preventing them from
doing things like killing, renicing, or changing the priority of the
gssd process while it is processing the context creation.

diff --git a/utils/gssd/gssd_proc.c b/utils/gssd/gssd_proc.c
index 75a04f5ba23744af9c0a347db1d9447cd5d60da3..c26849713d1e0ad41538b1d9157a8cac9371c4d3 100644 (file)
--- a/utils/gssd/gssd_proc.c
+++ b/utils/gssd/gssd_proc.c
@@ -493,13 +493,13 @@ int create_auth_rpc_client(struct clnt_info *clp,
 
        /* Create the context as the user (not as root) */
        save_uid = geteuid();
-       if (seteuid(uid) != 0) {
-               printerr(0, "WARNING: Failed to seteuid for "
+       if (setfsuid(uid) != 0) {
+               printerr(0, "WARNING: Failed to setfsuid for "
                            "user with uid %d\n", uid);
                goto out_fail;
        }
-       printerr(2, "creating context using euid %d (save_uid %d)\n",
-                       geteuid(), save_uid);
+       printerr(2, "creating context using fsuid %d (save_uid %d)\n",
+                       uid, save_uid);
 
        sec.qop = GSS_C_QOP_DEFAULT;
        sec.svc = RPCSEC_GSS_SVC_NONE;
@@ -646,9 +646,9 @@ int create_auth_rpc_client(struct clnt_info *clp,
                gss_release_cred(&min_stat, &sec.cred);
        if (a != NULL) freeaddrinfo(a);
        /* Restore euid to original value */
-       if ((save_uid != -1) && (seteuid(save_uid) != 0)) {
-               printerr(0, "WARNING: Failed to restore euid"
-                           " to uid %d\n", save_uid);
+       if ((save_uid != -1) && (setfsuid(save_uid) != uid)) {
+               printerr(0, "WARNING: Failed to restore fsuid"
+                           " to uid %d from %d\n", save_uid, uid);
        }
        return retval;