Re: [dpdk-dev] [PATCH] Fix `eventfd_link' module leakages and races

[Pavel Boldin <pboldin@mirantis.com>]

Changchun,

Please review the updated patch.

Pavel

On Tue, Mar 17, 2015 at 3:29 AM, Ouyang, Changchun <
changchun.ouyang@intel.com> wrote:

>
>
> > -----Original Message-----
> > From: dev [mailto:dev-bounces@dpdk.org] On Behalf Of Pavel Boldin
> > Sent: Tuesday, March 17, 2015 12:41 AM
> > To: dev@dpdk.org
> > Cc: Pavel Boldin
> > Subject: [dpdk-dev] [PATCH] Fix `eventfd_link' module leakages and races
> >
> > From: Pavel Boldin <pboldin@mirantis.com>
> >
> > The `eventfd_link' module provides an API to "steal" fd from another
> process
> > had been written with a bug that leaks `struct file' because of the extra
> > reference counter increment and missing `fput' call.
> >
> > The other bug is using another process' `task_struct' without
> incrementing a
> > reference counter.
> >
> > Fix these bugs and refactor the module.
> > ---
> >  examples/vhost/eventfd_link/eventfd_link.c | 236 ++++++++++++++++-----
> > --------
> >  1 file changed, 130 insertions(+), 106 deletions(-)
> >
> > diff --git a/examples/vhost/eventfd_link/eventfd_link.c
> > b/examples/vhost/eventfd_link/eventfd_link.c
> > index 69470ba..9f1f8fb 100644
> > --- a/examples/vhost/eventfd_link/eventfd_link.c
> > +++ b/examples/vhost/eventfd_link/eventfd_link.c
> > @@ -42,15 +42,15 @@
> >   * get_files_struct is copied from fs/file.c
> >   */
> >  struct files_struct *
> > -get_files_struct (struct task_struct *task)
> > +get_files_struct(struct task_struct *task)
> >  {
> >       struct files_struct *files;
> >
> > -     task_lock (task);
> > +     task_lock(task);
> >       files = task->files;
> >       if (files)
> > -             atomic_inc (&files->count);
> > -     task_unlock (task);
> > +             atomic_inc(&files->count);
> > +     task_unlock(task);
>
> I don't find any actual code change for above.
> If they are tab, space, indent refine,
> I suggest it needs a separate patch named code cleanup,
> Then it is easy to review.
>
> Same for other places.
>
> Done.
> Changchun
>
>
> >
> >       return files;
> >  }
> > @@ -59,117 +59,142 @@ get_files_struct (struct task_struct *task)
> >   * put_files_struct is extracted from fs/file.c
> >   */
> >  void
> > -put_files_struct (struct files_struct *files)
> > +put_files_struct(struct files_struct *files)
> >  {
> > -     if (atomic_dec_and_test (&files->count))
> > -     {
> > +     if (atomic_dec_and_test(&files->count))
> >               BUG ();
> > +}
> > +
> > +static struct file *
> > +fget_from_files(struct files_struct *files, unsigned fd) {
> > +     struct file *file;
> > +
> > +     rcu_read_lock();
> > +     file = fcheck_files(files, fd);
> > +     if (file)
> > +     {
> > +             if (file->f_mode & FMODE_PATH
> > +                     || !atomic_long_inc_not_zero(&file->f_count))
> > +                 file = NULL;
> >       }
> > +     rcu_read_unlock();
> > +
> > +     return file;
> > +}
> > +
> > +static int
> > +close_fd(unsigned fd)
> > +{
> > +     struct file *file;
> > +     struct files_struct *files = current->files;
> > +     struct fdtable *fdt;
> > +
> > +     spin_lock(&files->file_lock);
> > +     fdt = files_fdtable(files);
> > +     if (fd >= fdt->max_fds)
> > +             goto out_unlock;
> > +     file = fdt->fd[fd];
> > +     if (!file)
> > +             goto out_unlock;
> > +     rcu_assign_pointer(fdt->fd[fd], NULL);
> > +     __clear_bit(fd, fdt->close_on_exec);
> > +     spin_unlock(&files->file_lock);
> > +     return filp_close(file, files);
> > +
> > +out_unlock:
> > +     spin_unlock(&files->file_lock);
> > +     return -EBADF;
> >  }
> >
> >
> >  static long
> > -eventfd_link_ioctl (struct file *f, unsigned int ioctl, unsigned long
> arg)
> > +eventfd_link_ioctl_copy(unsigned long arg)
> >  {
> > -     void __user *argp = (void __user *) arg;
> > +     long ret = -EFAULT;
> >       struct task_struct *task_target = NULL;
> > -     struct file *file;
> > -     struct files_struct *files;
> > -     struct fdtable *fdt;
> > +     struct file *target_file = NULL;
> > +     struct files_struct *target_files = NULL;
> >       struct eventfd_copy eventfd_copy;
> > +     struct pid *pid;
> > +
> > +     if (copy_from_user(&eventfd_copy, (void __user*)arg,
> > +                         sizeof(struct eventfd_copy)))
> > +             goto out;
> > +
> > +     /*
> > +      * Find the task struct for the target pid
> > +      */
> > +     pid = find_vpid(eventfd_copy.target_pid);
> > +     if (pid == NULL) {
> > +             printk(KERN_INFO "Unable to find pid %d\n",
> > +                     eventfd_copy.target_pid);
> > +             goto out;
> > +     }
> > +
> > +     task_target = get_pid_task(pid, PIDTYPE_PID);
> > +     if (task_target == NULL) {
> > +             printk(KERN_INFO "Failed to get task for pid %d\n",
> > +                     eventfd_copy.target_pid);
> > +             goto out;
> > +     }
> > +
> > +     ret = close_fd(eventfd_copy.source_fd);
> > +     if (ret)
> > +             goto out_task;
> > +     ret = -EFAULT;
> > +
> > +     /*
> > +      * Find the file struct associated with the target fd.
> > +      */
> > +
> > +     target_files = get_files_struct(task_target);
> > +     if (target_files == NULL) {
> > +             printk (KERN_INFO "Failed to get target files struct\n");
> > +             goto out_task;
> > +     }
> > +
> > +     target_file = fget_from_files(target_files,
> eventfd_copy.target_fd);
> > +
> > +     if (target_file == NULL) {
> > +             printk (KERN_INFO "Failed to get file from target pid\n");
> > +             goto out_target_files;
> > +     }
> > +
> > +
> > +     /*
> > +      * Install the file struct from the target process into the
> > +      * file desciptor of the source process,
> > +      */
> > +
> > +     fd_install(eventfd_copy.source_fd, target_file);
> > +
> > +     ret = 0;
> > +
> > +out_target_files:
> > +     put_files_struct(target_files);
> > +out_task:
> > +     put_task_struct(task_target);
> > +out:
> > +     return ret;
> > +}
> > +
> > +static long
> > +eventfd_link_ioctl(struct file *f, unsigned int ioctl, unsigned long
> > +arg) {
> > +     long ret;
> >
> >       switch (ioctl)
> >       {
> >               case EVENTFD_COPY:
> > -                     if (copy_from_user (&eventfd_copy, argp, sizeof
> > (struct eventfd_copy)))
> > -                             return -EFAULT;
> > -
> > -                     /*
> > -                      * Find the task struct for the target pid
> > -                      */
> > -                     task_target =
> > -                             pid_task (find_vpid
> > (eventfd_copy.target_pid), PIDTYPE_PID);
> > -                     if (task_target == NULL)
> > -                     {
> > -                             printk (KERN_DEBUG "Failed to get mem ctx
> > for target pid\n");
> > -                             return -EFAULT;
> > -                     }
> > -
> > -                     files = get_files_struct (current);
> > -                     if (files == NULL)
> > -                     {
> > -                             printk (KERN_DEBUG "Failed to get files
> > struct\n");
> > -                             return -EFAULT;
> > -                     }
> > -
> > -                     rcu_read_lock ();
> > -                     file = fcheck_files (files,
> eventfd_copy.source_fd);
> > -                     if (file)
> > -                     {
> > -                             if (file->f_mode & FMODE_PATH
> > -
> >       || !atomic_long_inc_not_zero (&file->f_count))
> > -                                     file = NULL;
> > -                     }
> > -                     rcu_read_unlock ();
> > -                     put_files_struct (files);
> > -
> > -                     if (file == NULL)
> > -                     {
> > -                             printk (KERN_DEBUG "Failed to get file from
> > source pid\n");
> > -                             return 0;
> > -                     }
> > -
> > -                     /*
> > -                      * Release the existing eventfd in the source
> process
> > -                      */
> > -                     spin_lock (&files->file_lock);
> > -                     fput(file);
> > -                     filp_close (file, files);
> > -                     fdt = files_fdtable (files);
> > -                     fdt->fd[eventfd_copy.source_fd] = NULL;
> > -                     spin_unlock (&files->file_lock);
> > -
> > -                     /*
> > -                      * Find the file struct associated with the target
> fd.
> > -                      */
> > -
> > -                     files = get_files_struct (task_target);
> > -                     if (files == NULL)
> > -                     {
> > -                             printk (KERN_DEBUG "Failed to get files
> > struct\n");
> > -                             return -EFAULT;
> > -                     }
> > -
> > -                     rcu_read_lock ();
> > -                     file = fcheck_files (files,
> eventfd_copy.target_fd);
> > -                     if (file)
> > -                     {
> > -                             if (file->f_mode & FMODE_PATH
> > -
> >       || !atomic_long_inc_not_zero (&file->f_count))
> > -                                     file = NULL;
> > -                     }
> > -                     rcu_read_unlock ();
> > -                     put_files_struct (files);
> > -
> > -                     if (file == NULL)
> > -                     {
> > -                             printk (KERN_DEBUG "Failed to get file from
> > target pid\n");
> > -                             return 0;
> > -                     }
> > -
> > -
> > -                     /*
> > -                      * Install the file struct from the target process
> into
> > the
> > -                      * file desciptor of the source process,
> > -                      */
> > -
> > -                     fd_install (eventfd_copy.source_fd, file);
> > -
> > -                     return 0;
> > -
> > +                     ret = eventfd_link_ioctl_copy(arg);
> > +                     break;
> >               default:
> > -                     return -ENOIOCTLCMD;
> > +                     ret = -ENOIOCTLCMD;
> > +                     break;
> >       }
> > +
> > +     return ret;
> >  }
> >
> >  static const struct file_operations eventfd_link_fops = { @@ -184,21
> +209,20
> > @@ static struct miscdevice eventfd_link_misc = {  };
> >
> >  static int __init
> > -eventfd_link_init (void)
> > +eventfd_link_init(void)
> >  {
> > -     printk(KERN_INFO "eventfd_link is broken, use it at your risk\n");
> > -     return misc_register (&eventfd_link_misc);
> > +     return misc_register(&eventfd_link_misc);
> >  }
> >
> > -module_init (eventfd_link_init);
> > +module_init(eventfd_link_init);
> >
> >  static void __exit
> > -eventfd_link_exit (void)
> > +eventfd_link_exit(void)
> >  {
> > -     misc_deregister (&eventfd_link_misc);
> > +     misc_deregister(&eventfd_link_misc);
> >  }
> >
> > -module_exit (eventfd_link_exit);
> > +module_exit(eventfd_link_exit);
> >
> >  MODULE_VERSION ("0.0.1");
> >  MODULE_LICENSE ("GPL v2");
> > --
> > 1.9.1
>
>