[PATCH 3.18 65/84] userns: Allow setting gid_maps without privilege when setgroups is disabled

[Greg Kroah-Hartman]

3.18-stable review patch.  If anyone has any objections, please let me know.

------------------

From: "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx>

commit 66d2f338ee4c449396b6f99f5e75cd18eb6df272 upstream.

Now that setgroups can be disabled and not reenabled, setting gid_map
without privielge can now be enabled when setgroups is disabled.

This restores most of the functionality that was lost when unprivileged
setting of gid_map was removed.  Applications that use this functionality
will need to check to see if they use setgroups or init_groups, and if they
don't they can be fixed by simply disabling setgroups before writing to
gid_map.

Reviewed-by: Andy Lutomirski <luto@xxxxxxxxxxxxxx>
Signed-off-by: "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 kernel/user_namespace.c |    5 +++++
 1 file changed, 5 insertions(+)

--- a/kernel/user_namespace.c
+++ b/kernel/user_namespace.c
@@ -826,6 +826,11 @@ static bool new_idmap_permitted(const st
 			kuid_t uid = make_kuid(ns->parent, id);
 			if (uid_eq(uid, cred->euid))
 				return true;
+		} else if (cap_setid == CAP_SETGID) {
+			kgid_t gid = make_kgid(ns->parent, id);
+			if (!(ns->flags & USERNS_SETGROUPS_ALLOWED) &&
+			    gid_eq(gid, cred->egid))
+				return true;
 		}
 	}
 


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