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SubjectRe: [PATCH resend] user namespace: usb: make usb urbs user namespace aware (v2)
Quoting Alan Stern (stern@rowland.harvard.edu):
> On Fri, 23 Sep 2011, Serge E. Hallyn wrote:
>
> > (re-sending to Cc: Greg and linux-usb)
> >
> > Add to the dev_state and alloc_async structures the user namespace
> > corresponding to the uid and euid. Pass these to kill_pid_info_as_uid(),
> > which can then implement a proper, user-namespace-aware uid check.
> >
> > Changelog:
> > Sep 20: Per Oleg's suggestion: Instead of caching and passing user namespace,
> > uid, and euid each separately, pass a struct cred.
>
> This should be broken up into two separate patches: One to add
> kill_pid_info_as_cred() and the other to modify the usbfs driver.

It seems like that would make the first patch harder to review (since
it won't just show the changes from kill_pid_info_as_uid to
kill_pid_info_as_cred), but I'll go ahead and split it up. I assume
kill_pid_info_as_uid should be removed in a third patch?

> > --- a/drivers/usb/core/devio.c
> > +++ b/drivers/usb/core/devio.c
>
> > @@ -393,9 +395,8 @@ static void async_compled ted(struct urb *urb)
> > struct dev_state *ps = as->ps;
> > struct siginfo sinfo;
> > struct pid *pid = NULL;
> > - uid_t uid = 0;
> > - uid_t euid = 0;
> > u32 secid = 0;
> > + const struct cred *cred = NULL;
> > int signr;
> >
> > spin_lock(&ps->lock);
> > @@ -408,8 +409,7 @@ static void async_completed(struct urb *urb)
> > sinfo.si_code = SI_ASYNCIO;
> > sinfo.si_addr = as->userurb;
> > pid = as->pid;
> > - uid = as->uid;
> > - euid = as->euid;
> > + cred = as->cred;
> > secid = as->secid;
> > }
> > snoop(&urb->dev->dev, "urb complete\n");
> > @@ -423,8 +423,7 @@ static void async_completed(struct urb *urb)
> > spin_unlock(&ps->lock);
> >
> > if (signr)
> > - kill_pid_info_as_uid(sinfo.si_signo, &sinfo, pid, uid,
> > - euid, secid);
> > + kill_pid_info_as_cred(sinfo.si_signo, &sinfo, pid, cred, secid);
>
> This continues a bug that already exists in the current code. Once
> ps->lock is released, there is no guarantee that the async structure
> will still exist. It may already have been freed, and the reference to

Yikes. That makes sense. I'll fix that for the cred and the pid as well
then?

> as->cred may already have been dropped. That's why the local copies
> have to be made above. cred shouldn't be a simple copy of as->cred; it
> should also increment the reference count.
>
> > @@ -706,8 +705,7 @@ static int usbdev_open(struct inode *inode, struct file *file)
> > init_waitqueue_head(&ps->wait);
> > ps->discsignr = 0;
> > ps->disc_pid = get_pid(task_pid(current));
> > - ps->disc_uid = cred->uid;
> > - ps->disc_euid = cred->euid;
> > + ps->cred = get_cred(cred);
>
> You might as well get rid of the "cred" local variable. It isn't used
> for anything except this assignment.
>
> Alan Stern

Thanks for looking, Alan.

-serge


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