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SubjectRe: [PATCH resend] user namespace: usb: make usb urbs user namespace aware (v2)
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.

> --- a/drivers/usb/core/devio.c
> +++ b/drivers/usb/core/devio.c

> @@ -393,9 +395,8 @@ static void async_completed(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
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



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