pidns: Make the pidns proc mount/umount logic obvious.

Track the number of pids in the proc hash table.  When the number of
pids goes to 0 schedule work to unmount the kernel mount of proc.

Move the mount of proc into alloc_pid when we allocate the pid for
init.

Remove the surprising calls of pid_ns_release proc in fork and
proc_flush_task.  Those code paths really shouldn't know about proc
namespace implementation details and people have demonstrated several
times that finding and understanding those code paths is difficult and
non-obvious.

Because of the call path detach pid is alwasy called with the
rtnl_lock held free_pid is not allowed to sleep, so the work to
unmounting proc is moved to a work queue.  This has the side benefit
of not blocking the entire world waiting for the unnecessary
rcu_barrier in deactivate_locked_super.

In the process of making the code clear and obvious this fixes a bug
reported by Gao feng <gaofeng@cn.fujitsu.com> where we would leak a
mount of proc during clone(CLONE_NEWPID|CLONE_NEWNET) if copy_pid_ns
succeeded and copy_net_ns failed.

Acked-by: "Serge E. Hallyn" <serge@hallyn.com>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
This commit is contained in:
Eric W. Biederman 2012-08-01 10:33:47 -07:00
parent 17cf22c33e
commit 0a01f2cc39
6 changed files with 26 additions and 22 deletions

View file

@ -2590,10 +2590,6 @@ void proc_flush_task(struct task_struct *task)
proc_flush_task_mnt(upid->ns->proc_mnt, upid->nr,
tgid->numbers[i].nr);
}
upid = &pid->numbers[pid->level];
if (upid->nr == 1)
pid_ns_release_proc(upid->ns);
}
static struct dentry *proc_pid_instantiate(struct inode *dir,

View file

@ -155,11 +155,6 @@ void __init proc_root_init(void)
err = register_filesystem(&proc_fs_type);
if (err)
return;
err = pid_ns_prepare_proc(&init_pid_ns);
if (err) {
unregister_filesystem(&proc_fs_type);
return;
}
proc_self_init();
proc_symlink("mounts", NULL, "self/mounts");

View file

@ -21,6 +21,7 @@ struct pid_namespace {
struct kref kref;
struct pidmap pidmap[PIDMAP_ENTRIES];
int last_pid;
int nr_hashed;
struct task_struct *child_reaper;
struct kmem_cache *pid_cachep;
unsigned int level;
@ -32,6 +33,7 @@ struct pid_namespace {
struct bsd_acct_struct *bacct;
#endif
struct user_namespace *user_ns;
struct work_struct proc_work;
kgid_t pid_gid;
int hide_pid;
int reboot; /* group exit code if this pidns was rebooted */

View file

@ -1476,8 +1476,6 @@ static struct task_struct *copy_process(unsigned long clone_flags,
if (p->io_context)
exit_io_context(p);
bad_fork_cleanup_namespaces:
if (unlikely(clone_flags & CLONE_NEWPID))
pid_ns_release_proc(p->nsproxy->pid_ns);
exit_task_namespaces(p);
bad_fork_cleanup_mm:
if (p->mm)

View file

@ -36,6 +36,7 @@
#include <linux/pid_namespace.h>
#include <linux/init_task.h>
#include <linux/syscalls.h>
#include <linux/proc_fs.h>
#define pid_hashfn(nr, ns) \
hash_long((unsigned long)nr + (unsigned long)ns, pidhash_shift)
@ -270,8 +271,12 @@ void free_pid(struct pid *pid)
unsigned long flags;
spin_lock_irqsave(&pidmap_lock, flags);
for (i = 0; i <= pid->level; i++)
hlist_del_rcu(&pid->numbers[i].pid_chain);
for (i = 0; i <= pid->level; i++) {
struct upid *upid = pid->numbers + i;
hlist_del_rcu(&upid->pid_chain);
if (--upid->ns->nr_hashed == 0)
schedule_work(&upid->ns->proc_work);
}
spin_unlock_irqrestore(&pidmap_lock, flags);
for (i = 0; i <= pid->level; i++)
@ -293,6 +298,7 @@ struct pid *alloc_pid(struct pid_namespace *ns)
goto out;
tmp = ns;
pid->level = ns->level;
for (i = ns->level; i >= 0; i--) {
nr = alloc_pidmap(tmp);
if (nr < 0)
@ -303,17 +309,23 @@ struct pid *alloc_pid(struct pid_namespace *ns)
tmp = tmp->parent;
}
if (unlikely(is_child_reaper(pid))) {
if (pid_ns_prepare_proc(ns))
goto out_free;
}
get_pid_ns(ns);
pid->level = ns->level;
atomic_set(&pid->count, 1);
for (type = 0; type < PIDTYPE_MAX; ++type)
INIT_HLIST_HEAD(&pid->tasks[type]);
upid = pid->numbers + ns->level;
spin_lock_irq(&pidmap_lock);
for ( ; upid >= pid->numbers; --upid)
for ( ; upid >= pid->numbers; --upid) {
hlist_add_head_rcu(&upid->pid_chain,
&pid_hash[pid_hashfn(upid->nr, upid->ns)]);
upid->ns->nr_hashed++;
}
spin_unlock_irq(&pidmap_lock);
out:
@ -570,6 +582,7 @@ void __init pidmap_init(void)
/* Reserve PID 0. We never call free_pidmap(0) */
set_bit(0, init_pid_ns.pidmap[0].page);
atomic_dec(&init_pid_ns.pidmap[0].nr_free);
init_pid_ns.nr_hashed = 1;
init_pid_ns.pid_cachep = KMEM_CACHE(pid,
SLAB_HWCACHE_ALIGN | SLAB_PANIC);

View file

@ -72,6 +72,12 @@ static struct kmem_cache *create_pid_cachep(int nr_ids)
return NULL;
}
static void proc_cleanup_work(struct work_struct *work)
{
struct pid_namespace *ns = container_of(work, struct pid_namespace, proc_work);
pid_ns_release_proc(ns);
}
/* MAX_PID_NS_LEVEL is needed for limiting size of 'struct pid' */
#define MAX_PID_NS_LEVEL 32
@ -105,6 +111,7 @@ static struct pid_namespace *create_pid_namespace(struct user_namespace *user_ns
ns->level = level;
ns->parent = get_pid_ns(parent_pid_ns);
ns->user_ns = get_user_ns(user_ns);
INIT_WORK(&ns->proc_work, proc_cleanup_work);
set_bit(0, ns->pidmap[0].page);
atomic_set(&ns->pidmap[0].nr_free, BITS_PER_PAGE - 1);
@ -112,15 +119,8 @@ static struct pid_namespace *create_pid_namespace(struct user_namespace *user_ns
for (i = 1; i < PIDMAP_ENTRIES; i++)
atomic_set(&ns->pidmap[i].nr_free, BITS_PER_PAGE);
err = pid_ns_prepare_proc(ns);
if (err)
goto out_put_parent_pid_ns;
return ns;
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: