2011-02-19 17:02:55

by Oleg Nesterov

Subject: Re: + userns-add-a-user_namespace-as-creator-owner-of-uts_namespace.patch added to -mm tree

> Subject: userns: add a user_namespace as creator/owner of uts_namespace
> From: "Serge E. Hallyn" <[email protected]>

Minor nit... feel free to ignore, but can't resist.

--- a/kernel/nsproxy.c~userns-add-a-user_namespace-as-creator-owner-of-uts_namespace
+++ a/kernel/nsproxy.c
@@ -74,6 +74,11 @@ static struct nsproxy *create_new_namesp
err = PTR_ERR(new_nsp->uts_ns);
goto out_uts;
}
+ if (new_nsp->uts_ns != tsk->nsproxy->uts_ns) {
+ put_user_ns(new_nsp->uts_ns->user_ns);
+ new_nsp->uts_ns->user_ns = task_cred_xxx(tsk, user)->user_ns;
+ get_user_ns(new_nsp->uts_ns->user_ns);
+ }

Looks correct, but confusing imho.

"new_nsp->uts_ns != tsk->nsproxy->uts_ns" is a bit strange way to
check "flags & CLONE_NEWUTS", no?

And since copy_utsname() already checks CLONE_NEWUTS, can't we move
this code into copy_utsname() or clone_uts_ns() ?

This way we can also avoid the unnecessary put_user_ns(new_nsp->user_ns)
above and get_user_ns(ns->user_ns) in create_uts_ns().

The same for "userns: add a user namespace owner of ipc ns" patch, at
first glance.


Once again, this is minor. But nsproxy repeats this pattern again and
again. For example, why copy_utsname() does get_uts_ns() unconditionally?
Or copy_namespaces()->get_nsproxy() ? Of course, I do not mean the tiny
performance penalty in the unlikely case. But this complicates the
understanding of this code, imho the simple cleanup below makes sense.

Oleg.

kernel/nsproxy.c | 30 ++++++++++--------------------
kernel/utsname.c | 13 ++++---------
2 files changed, 14 insertions(+), 29 deletions(-)

--- x/kernel/nsproxy.c
+++ x/kernel/nsproxy.c
@@ -120,22 +120,19 @@ int copy_namespaces(unsigned long flags,
{
struct nsproxy *old_ns = tsk->nsproxy;
struct nsproxy *new_ns;
- int err = 0;

if (!old_ns)
return 0;

- get_nsproxy(old_ns);
-
if (!(flags & (CLONE_NEWNS | CLONE_NEWUTS | CLONE_NEWIPC |
- CLONE_NEWPID | CLONE_NEWNET)))
+ CLONE_NEWPID | CLONE_NEWNET))) {
+ get_nsproxy(old_ns);
return 0;
-
- if (!capable(CAP_SYS_ADMIN)) {
- err = -EPERM;
- goto out;
}

+ if (!capable(CAP_SYS_ADMIN))
+ return -EPERM;
+
/*
* CLONE_NEWIPC must detach from the undolist: after switching
* to a new ipc namespace, the semaphore arrays from the old
@@ -143,22 +140,15 @@ int copy_namespaces(unsigned long flags,
* means share undolist with parent, so we must forbid using
* it along with CLONE_NEWIPC.
*/
- if ((flags & CLONE_NEWIPC) && (flags & CLONE_SYSVSEM)) {
- err = -EINVAL;
- goto out;
- }
+ if ((flags & CLONE_NEWIPC) && (flags & CLONE_SYSVSEM))
+ return -EINVAL;

new_ns = create_new_namespaces(flags, tsk, tsk->fs);
- if (IS_ERR(new_ns)) {
- err = PTR_ERR(new_ns);
- goto out;
- }
+ if (IS_ERR(new_ns))
+ return PTR_ERR(new_ns);

tsk->nsproxy = new_ns;
-
-out:
- put_nsproxy(old_ns);
- return err;
+ return 0;
}

void free_nsproxy(struct nsproxy *ns)
--- x/kernel/utsname.c
+++ x/kernel/utsname.c
@@ -52,18 +52,13 @@ static struct uts_namespace *clone_uts_n
*/
struct uts_namespace *copy_utsname(unsigned long flags, struct uts_namespace *old_ns)
{
- struct uts_namespace *new_ns;
-
BUG_ON(!old_ns);
- get_uts_ns(old_ns);

- if (!(flags & CLONE_NEWUTS))
- return old_ns;
+ if (unlikely(flags & CLONE_NEWUTS))
+ return clone_uts_ns(old_ns);

- new_ns = clone_uts_ns(old_ns);
-
- put_uts_ns(old_ns);
- return new_ns;
+ get_uts_ns(old_ns);
+ return old_ns;
}

void free_uts_ns(struct kref *kref)

2011-02-20 22:28:48

by Serge E. Hallyn

Subject: Re: + userns-add-a-user_namespace-as-creator-owner-of-uts_namespace.patch added to -mm tree

Quoting Oleg Nesterov ([email protected]):
> > Subject: userns: add a user_namespace as creator/owner of uts_namespace
> > From: "Serge E. Hallyn" <[email protected]>
>
> Minor nit... feel free to ignore, but can't resist.
>
> --- a/kernel/nsproxy.c~userns-add-a-user_namespace-as-creator-owner-of-uts_namespace
> +++ a/kernel/nsproxy.c
> @@ -74,6 +74,11 @@ static struct nsproxy *create_new_namesp
> err = PTR_ERR(new_nsp->uts_ns);
> goto out_uts;
> }
> + if (new_nsp->uts_ns != tsk->nsproxy->uts_ns) {
> + put_user_ns(new_nsp->uts_ns->user_ns);
> + new_nsp->uts_ns->user_ns = task_cred_xxx(tsk, user)->user_ns;
> + get_user_ns(new_nsp->uts_ns->user_ns);
> + }
>
> Looks correct, but confusing imho.
>
> "new_nsp->uts_ns != tsk->nsproxy->uts_ns" is a bit strange way to
> check "flags & CLONE_NEWUTS", no?
>
> And since copy_utsname() already checks CLONE_NEWUTS, can't we move
> this code into copy_utsname() or clone_uts_ns() ?

Yup. I had only found the bug this addresses very late so sort of
felt I should keep it as an obvious band-aid for now. I've got a
lot of feedback to address on this set (!), and I'll do this more
cleanly as well.

Thanks for taking a look, Oleg.

-serge