Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace

Pull (again) user namespace infrastructure changes from Eric Biederman:
 "Those bugs, those darn embarrasing bugs just want don't want to get
  fixed.

  Linus I just updated my mirror of your kernel.org tree and it appears
  you successfully pulled everything except the last 4 commits that fix
  those embarrasing bugs.

  When you get a chance can you please repull my branch"

* 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace:
  userns: Fix typo in description of the limitation of userns_install
  userns: Add a more complete capability subset test to commit_creds
  userns: Require CAP_SYS_ADMIN for most uses of setns.
  Fix cap_capable to only allow owners in the parent user namespace to have caps.

4 files changed, 31 insertions, 4 deletions

diff --git a/kernel/cred.c b/kernel/cred.c
index 8888afb846e9..e0573a43c7df 100644
--- a/kernel/cred.c
+++ b/kernel/cred.c
@@ -372,6 +372,31 @@ error_put:
         return ret;
 }
 
+static bool cred_cap_issubset(const struct cred *set, const struct cred *subset)
+{
+        const struct user_namespace *set_ns = set->user_ns;
+        const struct user_namespace *subset_ns = subset->user_ns;
+
+        /* If the two credentials are in the same user namespace see if
+         * the capabilities of subset are a subset of set.
+         */
+        if (set_ns == subset_ns)
+                return cap_issubset(subset->cap_permitted, set->cap_permitted);
+
+        /* The credentials are in a different user namespaces
+         * therefore one is a subset of the other only if a set is an
+         * ancestor of subset and set->euid is owner of subset or one
+         * of subsets ancestors.
+         */
+        for (;subset_ns != &init_user_ns; subset_ns = subset_ns->parent) {
+                if ((set_ns == subset_ns->parent)  &&
+                    uid_eq(subset_ns->owner, set->euid))
+                        return true;
+        }
+
+        return false;
+}
+
 /**
  * commit_creds - Install new credentials upon the current task
  * @new: The credentials to be assigned
@@ -410,7 +435,7 @@ int commit_creds(struct cred *new)
             !gid_eq(old->egid, new->egid) ||
             !uid_eq(old->fsuid, new->fsuid) ||
             !gid_eq(old->fsgid, new->fsgid) ||
-            !cap_issubset(new->cap_permitted, old->cap_permitted)) {
+            !cred_cap_issubset(old, new)) {
                 if (task->mm)
                         set_dumpable(task->mm, suid_dumpable);
                 task->pdeath_signal = 0;
diff --git a/kernel/pid_namespace.c b/kernel/pid_namespace.c
index 560da0dab230..fdbd0cdf271a 100644
--- a/kernel/pid_namespace.c
+++ b/kernel/pid_namespace.c
@@ -325,7 +325,8 @@ static int pidns_install(struct nsproxy *nsproxy, void *ns)
         struct pid_namespace *active = task_active_pid_ns(current);
         struct pid_namespace *ancestor, *new = ns;
 
-        if (!ns_capable(new->user_ns, CAP_SYS_ADMIN))
+        if (!ns_capable(new->user_ns, CAP_SYS_ADMIN) ||
+            !nsown_capable(CAP_SYS_ADMIN))
                 return -EPERM;
 
         /*
diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c
index f5975ccf9348..2b042c42fbc4 100644
--- a/kernel/user_namespace.c
+++ b/kernel/user_namespace.c
@@ -799,7 +799,7 @@ static int userns_install(struct nsproxy *nsproxy, void *ns)
         if (user_ns == current_user_ns())
                 return -EINVAL;
 
-        /* Threaded many not enter a different user namespace */
+        /* Threaded processes may not enter a different user namespace */
         if (atomic_read(&current->mm->mm_users) > 1)
                 return -EINVAL;
 
diff --git a/kernel/utsname.c b/kernel/utsname.c
index f6336d51d64c..08b197e8c485 100644
--- a/kernel/utsname.c
+++ b/kernel/utsname.c
@@ -113,7 +113,8 @@ static int utsns_install(struct nsproxy *nsproxy, void *new)
 {
         struct uts_namespace *ns = new;
 
-        if (!ns_capable(ns->user_ns, CAP_SYS_ADMIN))
+        if (!ns_capable(ns->user_ns, CAP_SYS_ADMIN) ||
+            !nsown_capable(CAP_SYS_ADMIN))
                 return -EPERM;
 
         get_uts_ns(ns);