pidns: Capture the user namespace and filter ns_last_pid

- Capture the the user namespace that creates the pid namespace
- Use that user namespace to test if it is ok to write to
  /proc/sys/kernel/ns_last_pid.

Zhao Hongjiang <zhaohongjiang@huawei.com> noticed I was missing a put_user_ns
in when destroying a pid_ns.  I have foloded his patch into this one
so that bisects will work properly.

Acked-by: Serge Hallyn <serge.hallyn@canonical.com>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>

1 files changed, 12 insertions, 5 deletions

diff --git a/kernel/pid_namespace.c b/kernel/pid_namespace.c
index 7b07cc0dfb75..b2604950aa50 100644
--- a/kernel/pid_namespace.c
+++ b/kernel/pid_namespace.c
@@ -10,6 +10,7 @@
 
 #include <linux/pid.h>
 #include <linux/pid_namespace.h>
+#include <linux/user_namespace.h>
 #include <linux/syscalls.h>
 #include <linux/err.h>
 #include <linux/acct.h>
@@ -74,7 +75,8 @@ err_alloc:
 /* MAX_PID_NS_LEVEL is needed for limiting size of 'struct pid' */
 #define MAX_PID_NS_LEVEL 32
 
-static struct pid_namespace *create_pid_namespace(struct pid_namespace *parent_pid_ns)
+static struct pid_namespace *create_pid_namespace(struct user_namespace *user_ns,
+        struct pid_namespace *parent_pid_ns)
 {
         struct pid_namespace *ns;
         unsigned int level = parent_pid_ns->level + 1;
@@ -102,6 +104,7 @@ static struct pid_namespace *create_pid_namespace(struct pid_namespace *parent_p
         kref_init(&ns->kref);
         ns->level = level;
         ns->parent = get_pid_ns(parent_pid_ns);
+        ns->user_ns = get_user_ns(user_ns);
 
         set_bit(0, ns->pidmap[0].page);
         atomic_set(&ns->pidmap[0].nr_free, BITS_PER_PAGE - 1);
@@ -117,6 +120,7 @@ static struct pid_namespace *create_pid_namespace(struct pid_namespace *parent_p
 
 out_put_parent_pid_ns:
         put_pid_ns(parent_pid_ns);
+        put_user_ns(user_ns);
 out_free_map:
         kfree(ns->pidmap[0].page);
 out_free:
@@ -131,16 +135,18 @@ static void destroy_pid_namespace(struct pid_namespace *ns)
 
         for (i = 0; i < PIDMAP_ENTRIES; i++)
                 kfree(ns->pidmap[i].page);
+        put_user_ns(ns->user_ns);
         kmem_cache_free(pid_ns_cachep, ns);
 }
 
-struct pid_namespace *copy_pid_ns(unsigned long flags, struct pid_namespace *old_ns)
+struct pid_namespace *copy_pid_ns(unsigned long flags,
+        struct user_namespace *user_ns, struct pid_namespace *old_ns)
 {
         if (!(flags & CLONE_NEWPID))
                 return get_pid_ns(old_ns);
         if (flags & (CLONE_THREAD|CLONE_PARENT))
                 return ERR_PTR(-EINVAL);
-        return create_pid_namespace(old_ns);
+        return create_pid_namespace(user_ns, old_ns);
 }
 
 static void free_pid_ns(struct kref *kref)
@@ -239,9 +245,10 @@ void zap_pid_ns_processes(struct pid_namespace *pid_ns)
 static int pid_ns_ctl_handler(struct ctl_table *table, int write,
                 void __user *buffer, size_t *lenp, loff_t *ppos)
 {
+        struct pid_namespace *pid_ns = task_active_pid_ns(current);
         struct ctl_table tmp = *table;
 
-        if (write && !capable(CAP_SYS_ADMIN))
+        if (write && !ns_capable(pid_ns->user_ns, CAP_SYS_ADMIN))
                 return -EPERM;
 
         /*
@@ -250,7 +257,7 @@ static int pid_ns_ctl_handler(struct ctl_table *table, int write,
          * it should synchronize its usage with external means.
          */
 
-        tmp.data = &current->nsproxy->pid_ns->last_pid;
+        tmp.data = &pid_ns->last_pid;
         return proc_dointvec_minmax(&tmp, write, buffer, lenp, ppos);
 }