Merge branch 'userns-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/luto/linux

Pull user-namespace fixes from Andy Lutomirski.

* 'userns-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/luto/linux:
  userns: Changing any namespace id mappings should require privileges
  userns: Check uid_map's opener's fsuid, not the current fsuid
  userns: Don't let unprivileged users trick privileged users into setting the id_map

1 files changed, 13 insertions, 9 deletions

diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c
index a54f26f82eb2..e134d8f365dd 100644
--- a/kernel/user_namespace.c
+++ b/kernel/user_namespace.c
@@ -25,7 +25,8 @@
 
 static struct kmem_cache *user_ns_cachep __read_mostly;
 
-static bool new_idmap_permitted(struct user_namespace *ns, int cap_setid,
+static bool new_idmap_permitted(const struct file *file,
+                                struct user_namespace *ns, int cap_setid,
                                 struct uid_gid_map *map);
 
 static void set_cred_user_ns(struct cred *cred, struct user_namespace *user_ns)
@@ -612,10 +613,10 @@ static ssize_t map_write(struct file *file, const char __user *buf,
         if (map->nr_extents != 0)
                 goto out;
 
-        /* Require the appropriate privilege CAP_SETUID or CAP_SETGID
-         * over the user namespace in order to set the id mapping.
+        /*
+         * Adjusting namespace settings requires capabilities on the target.
          */
-        if (cap_valid(cap_setid) && !ns_capable(ns, cap_setid))
+        if (cap_valid(cap_setid) && !file_ns_capable(file, ns, CAP_SYS_ADMIN))
                 goto out;
 
         /* Get a buffer */
@@ -700,7 +701,7 @@ static ssize_t map_write(struct file *file, const char __user *buf,
 
         ret = -EPERM;
         /* Validate the user is allowed to use user id's mapped to. */
-        if (!new_idmap_permitted(ns, cap_setid, &new_map))
+        if (!new_idmap_permitted(file, ns, cap_setid, &new_map))
                 goto out;
 
         /* Map the lower ids from the parent user namespace to the
@@ -787,7 +788,8 @@ ssize_t proc_projid_map_write(struct file *file, const char __user *buf, size_t
                          &ns->projid_map, &ns->parent->projid_map);
 }
 
-static bool new_idmap_permitted(struct user_namespace *ns, int cap_setid,
+static bool new_idmap_permitted(const struct file *file, 
+                                struct user_namespace *ns, int cap_setid,
                                 struct uid_gid_map *new_map)
 {
         /* Allow mapping to your own filesystem ids */
@@ -795,12 +797,12 @@ static bool new_idmap_permitted(struct user_namespace *ns, int cap_setid,
                 u32 id = new_map->extent[0].lower_first;
                 if (cap_setid == CAP_SETUID) {
                         kuid_t uid = make_kuid(ns->parent, id);
-                        if (uid_eq(uid, current_fsuid()))
+                        if (uid_eq(uid, file->f_cred->fsuid))
                                 return true;
                 }
                 else if (cap_setid == CAP_SETGID) {
                         kgid_t gid = make_kgid(ns->parent, id);
-                        if (gid_eq(gid, current_fsgid()))
+                        if (gid_eq(gid, file->f_cred->fsgid))
                                 return true;
                 }
         }
@@ -811,8 +813,10 @@ static bool new_idmap_permitted(struct user_namespace *ns, int cap_setid,
 
         /* Allow the specified ids if we have the appropriate capability
          * (CAP_SETUID or CAP_SETGID) over the parent user namespace.
+         * And the opener of the id file also had the approprpiate capability.
          */
-        if (ns_capable(ns->parent, cap_setid))
+        if (ns_capable(ns->parent, cap_setid) &&
+            file_ns_capable(file, ns->parent, cap_setid))
                 return true;
 
         return false;