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proc: Usable inode numbers for the namespace file descriptors.

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Assign a unique proc inode to each namespace, and use that
inode number to ensure we only allocate at most one proc
inode for every namespace in proc.

A single proc inode per namespace allows userspace to test
to see if two processes are in the same namespace.

This has been a long requested feature and only blocked because
a naive implementation would put the id in a global space and
would ultimately require having a namespace for the names of
namespaces, making migration and certain virtualization tricks
impossible.

We still don't have per superblock inode numbers for proc, which
appears necessary for application unaware checkpoint/restart and
migrations (if the application is using namespace file descriptors)
but that is now allowd by the design if it becomes important.

I have preallocated the ipc and uts initial proc inode numbers so
their structures can be statically initialized.

Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
This commit is contained in:
Eric W. Biederman
2011-06-15 10:21:48 -07:00
parent bf056bfa80
commit 98f842e675
18 changed files with 132 additions and 12 deletions
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15
kernel/user_namespace.c
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@@ -58,6 +58,7 @@ int create_user_ns(struct cred *new)
struct user_namespace *ns, *parent_ns = new->user_ns;
kuid_t owner = new->euid;
kgid_t group = new->egid;
int ret;
/* The creator needs a mapping in the parent user namespace
* or else we won't be able to reasonably tell userspace who
@@ -71,6 +72,12 @@ int create_user_ns(struct cred *new)
if (!ns)
return -ENOMEM;
ret = proc_alloc_inum(&ns->proc_inum);
if (ret) {
kmem_cache_free(user_ns_cachep, ns);
return ret;
}
kref_init(&ns->kref);
/* Leave the new->user_ns reference with the new user namespace. */
ns->parent = parent_ns;
@@ -103,6 +110,7 @@ void free_user_ns(struct kref *kref)
container_of(kref, struct user_namespace, kref);
parent = ns->parent;
proc_free_inum(ns->proc_inum);
kmem_cache_free(user_ns_cachep, ns);
put_user_ns(parent);
}
@@ -808,12 +816,19 @@ static int userns_install(struct nsproxy *nsproxy, void *ns)
return commit_creds(cred);
}
static unsigned int userns_inum(void *ns)
{
struct user_namespace *user_ns = ns;
return user_ns->proc_inum;
}
const struct proc_ns_operations userns_operations = {
.name = "user",
.type = CLONE_NEWUSER,
.get = userns_get,
.put = userns_put,
.install = userns_install,
.inum = userns_inum,
};
static __init int user_namespaces_init(void)