USB: fix race leading to a write after kfree in usbfs

this fixes a race between async_completed() and proc_reapurbnonblock().

CPU A                   CPU B

spin_lock(&ps->lock);
list_move_tail(&as->asynclist, &ps->async_completed);
spin_unlock(&ps->lock);

                                if (!(as = async_getcompleted(ps)))
                                        return -EAGAIN;
                                return processcompl(as, (void __user * __user *)arg);

processcompl() calls free_async() which calls kfree(as)

as->status = urb->status;
if (as->signr) {
        sinfo.si_signo = as->signr;
        sinfo.si_errno = as->status;
        sinfo.si_code = SI_ASYNCIO;
        sinfo.si_addr = as->userurb;
        kill_pid_info_as_uid(as->signr, &sinfo, as->pid, as->uid,
                              as->euid, as->secid);
}
snoop(&urb->dev->dev, "urb complete\n");
snoop_urb(urb, as->userurb);

write after kfree

Signed-off-by: Oliver Neukum <oliver@neukum.org>

diff --git a/drivers/usb/core/devio.c b/drivers/usb/core/devio.c
index 706f181..46ca2af 100644 (file)
--- a/drivers/usb/core/devio.c
+++ b/drivers/usb/core/devio.c
@@ -325,21 +325,34 @@ static void async_completed(struct urb *urb)
        struct async *as = urb->context;
        struct dev_state *ps = as->ps;
        struct siginfo sinfo;
+       struct pid *pid = NULL;
+       uid_t uid = 0;
+       uid_t euid = 0;
+       u32 secid = 0;
+       int signr;
 
        spin_lock(&ps->lock);
        list_move_tail(&as->asynclist, &ps->async_completed);
-       spin_unlock(&ps->lock);
        as->status = urb->status;
-       if (as->signr) {
+       signr = as->signr;
+       if (signr) {
                sinfo.si_signo = as->signr;
                sinfo.si_errno = as->status;
                sinfo.si_code = SI_ASYNCIO;
                sinfo.si_addr = as->userurb;
-               kill_pid_info_as_uid(as->signr, &sinfo, as->pid, as->uid,
-                                     as->euid, as->secid);
+               pid = as->pid;
+               uid = as->uid;
+               euid = as->euid;
+               secid = as->secid;
        }
        snoop(&urb->dev->dev, "urb complete\n");
        snoop_urb(urb, as->userurb);
+       spin_unlock(&ps->lock);
+
+       if (signr)
+               kill_pid_info_as_uid(sinfo.si_signo, &sinfo, pid, uid,
+                                     euid, secid);
+
        wake_up(&ps->wait);
 }