[PATCH v3 12/13] epoll: support mapping for epfd when polled from userspace

Roman Penyaev
2019-05-16T08:58:54Z

User has to mmap user_header and user_index vmalloce'd pointers in order
to consume events from userspace. Also we do not let any copies of vma
on fork().

Signed-off-by: Roman Penyaev <rpenyaev@suse.de>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: linux-fsdevel@vger.kernel.org
Cc: linux-kernel@vger.kernel.org

diff --git a/fs/eventpoll.c b/fs/eventpoll.c
index 20c94587488f..9ff666ce7cb5 100644
--- a/fs/eventpoll.c
+++ b/fs/eventpoll.c
@@ -1276,11 +1276,47 @@ static void ep_show_fdinfo(struct seq_file *m, struct file *f)
}
#endif

+static int ep_eventpoll_mmap(struct file *filep, struct vm_area_struct *vma)
+{
+ struct eventpoll *ep = vma->vm_file->private_data;
+ size_t size;
+ int rc;
+
+ if (!ep_polled_by_user(ep))
+ return -ENOTSUPP;
+
+ size = vma->vm_end - vma->vm_start;
+ if (!vma->vm_pgoff && size > ep->header_length)
+ return -ENXIO;
+ if (vma->vm_pgoff && ep->header_length != (vma->vm_pgoff << PAGE_SHIFT))
+ /* Index ring starts exactly after the header */
+ return -ENXIO;
+ if (vma->vm_pgoff && size > ep->index_length)
+ return -ENXIO;
+
+ /*
+ * vm_pgoff is used *only* for indication, what is mapped: user header
+ * or user index ring. Sizes are checked above.
+ */
+ if (!vma->vm_pgoff)
+ rc = remap_vmalloc_range_partial(vma, vma->vm_start,
+ ep->user_header, size);
+ else
+ rc = remap_vmalloc_range_partial(vma, vma->vm_start,
+ ep->user_index, size);
+ if (likely(!rc))
+ /* No copies for forks(), please */
+ vma->vm_flags |= VM_DONTCOPY;
+
+ return rc;
+}
+
/* File callbacks that implement the eventpoll file behaviour */
static const struct file_operations eventpoll_fops = {
#ifdef CONFIG_PROC_FS
.show_fdinfo = ep_show_fdinfo,
#endif
+ .mmap = ep_eventpoll_mmap,
.release = ep_eventpoll_release,
.poll = ep_eventpoll_poll,
.llseek = noop_llseek,
--
2.21.0