On Thu, Aug 10, 2017 at 8:46 PM, Andrei Vagin <avagin@xxxxxxxxxx> wrote:
> It is a hybrid of process_vm_readv() and vmsplice().
>
> vmsplice can map memory from a current address space into a pipe.
> process_vm_readv can read memory of another process.
[...]
> +/*
> + * Map pages from a specified task into a pipe
> + */
> +static int remote_single_vec_to_pipe(struct task_struct *task,
> + struct mm_struct *mm,
> + const struct iovec *rvec,
> + struct pipe_inode_info *pipe,
> + unsigned int flags,
> + size_t *total)
> +{
> + struct pipe_buffer buf = {
> + .ops = &user_page_pipe_buf_ops,
> + .flags = flags
> + };
[...]
> + while (nr_pages) {
[...]
> + /*
> + * Get the pages we're interested in. We must
> + * access remotely because task/mm might not
> + * current/current->mm
> + */
> + down_read(&mm->mmap_sem);
> + pages = get_user_pages_remote(task, mm, pa, pages, flags,
> + process_pages, NULL, &locked);
This fifth "flags" argument of get_user_pages_remote() should contain
GUP flags (FOLL_*), but it looks like you're actually passing in 0 or
PIPE_BUF_FLAG_GIFT, which will be interpreted as FOLL_GET?
(See the snippets quoted below.) This looks like a bug.
Maybe use a more meaningful variable name than "flags".
> +static ssize_t remote_iovec_to_pipe(struct task_struct *task,
> + struct mm_struct *mm,
> + const struct iovec *rvec,
> + unsigned long riovcnt,
> + struct pipe_inode_info *pipe,
> + unsigned int flags)
> +{
[...]
> + ret = remote_single_vec_to_pipe(
> + task, mm, &rvec[i], pipe, flags, &total);
[...]
> +}
> +
> +static long process_vmsplice_to_pipe(struct task_struct *task,
> + struct mm_struct *mm, struct file *file,
> + const struct iovec __user *uiov,
> + unsigned long nr_segs, unsigned int flags)
> +{
[...]
> + unsigned int buf_flag = 0;
[...]
> + if (flags & SPLICE_F_GIFT)
> + buf_flag = PIPE_BUF_FLAG_GIFT;
[...]
> + if (!ret)
> + ret = remote_iovec_to_pipe(task, mm, iov,
> + nr_segs, pipe, buf_flag);
[...]
> +}
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