[hurd, commited 3/3] hurd: Preserve the euid/egid in seteuids/setgroups.

[Samuel Thibault]

From: Yelninei <yelni...@tutamail.com>

By convention the first uid/gid is the euid/egid. Ensure that the
first uid/gid in the array passed to auth_makeauth is the egid/egid to
not unexpectedly overwrite it.
---
 hurd/seteuids.c               | 17 +++++++++++++----
 sysdeps/mach/hurd/setgroups.c | 17 +++++++++++++----
 2 files changed, 26 insertions(+), 8 deletions(-)

diff --git a/hurd/seteuids.c b/hurd/seteuids.c
index 3be772ae8b..8c4f5f2c20 100644
--- a/hurd/seteuids.c
+++ b/hurd/seteuids.c
@@ -15,6 +15,7 @@
    License along with the GNU C Library; if not, see
    <https://www.gnu.org/licenses/>.  */
 
+#include <unistd.h>
 #include <hurd.h>
 #include <hurd/id.h>
 
@@ -24,12 +25,20 @@ seteuids (size_t n, const uid_t *uids)
 {
   error_t err;
   auth_t newauth;
-  size_t i;
-  gid_t new[n];
+  size_t i, start;
+  uid_t euid;
+  uid_t new[n + 1];
 
+  start = 0;
+  euid = geteuid ();
+  if (euid != (uid_t) -1 && (n == 0 || (n > 0 && euid != uids[0])))
+    {
+      new[0] = euid;
+      start = 1;
+    }
   /* Fault before taking locks.  */
   for (i = 0; i < n; ++i)
-    new[i] = uids[i];
+    new[i + start] = uids[i];
 
 retry:
   HURD_CRITICAL_BEGIN;
@@ -40,7 +49,7 @@ retry:
       /* Get a new auth port using those IDs.  */
       err = __USEPORT (AUTH,
                       __auth_makeauth (port, NULL, MACH_MSG_TYPE_COPY_SEND, 0,
-                                       new, n,
+                                       new, n + start,
                                        _hurd_id.aux.uids, _hurd_id.aux.nuids,
                                        _hurd_id.gen.gids, _hurd_id.gen.ngids,
                                        _hurd_id.aux.gids, _hurd_id.aux.ngids,
diff --git a/sysdeps/mach/hurd/setgroups.c b/sysdeps/mach/hurd/setgroups.c
index 5d71d89011..ddfed7cac5 100644
--- a/sysdeps/mach/hurd/setgroups.c
+++ b/sysdeps/mach/hurd/setgroups.c
@@ -17,6 +17,7 @@
 
 #include <errno.h>
 #include <sys/types.h>
+#include <unistd.h>
 #include <grp.h>
 #include <hurd.h>
 #include <hurd/id.h>
@@ -27,12 +28,20 @@ setgroups (size_t n, const gid_t *groups)
 {
   error_t err;
   auth_t newauth;
-  size_t i;
-  gid_t new[n];
+  size_t i, start;
+  gid_t egid;
+  gid_t new[n + 1];
 
+  start = 0;
+  egid = getegid ();
+  if (egid != (gid_t) -1 && (n == 0 || (n > 0 && egid != groups[0])))
+    {
+      new[0] = egid;
+      start = 1;
+    }
   /* Fault before taking locks.  */
   for (i = 0; i < n; ++i)
-    new[i] = groups[i];
+    new[i + start] = groups[i];
 
 retry:
   HURD_CRITICAL_BEGIN;
@@ -45,7 +54,7 @@ retry:
                       __auth_makeauth (port, NULL, MACH_MSG_TYPE_COPY_SEND, 0,
                                        _hurd_id.gen.uids, _hurd_id.gen.nuids,
                                        _hurd_id.aux.uids, _hurd_id.aux.nuids,
-                                       new, n,
+                                       new, n + start,
                                        _hurd_id.aux.gids, _hurd_id.aux.ngids,
                                        &newauth));
     }
-- 
2.53.0