[PATCH for-next 1/4] io_uring/rsrc: disallow multi-source reg buffers

[Pavel Begunkov <asml.silence@gmail.com>]

If two or more mappings go back to back to each other they can be passed
into io_uring to be registered as a single registered buffer. That would
even work if mappings came from different sources, e.g. it's possible to
mix in this way anon pages and pages from shmem or hugetlb. That is not
a problem but it'd rather be less prone if we forbid such mixing.

Cc: <stable@vger.kernel.org>
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
---
 io_uring/rsrc.c | 13 ++++++++-----
 1 file changed, 8 insertions(+), 5 deletions(-)

diff --git a/io_uring/rsrc.c b/io_uring/rsrc.c
index a59fc02de598..8d7eb1548a04 100644
--- a/io_uring/rsrc.c
+++ b/io_uring/rsrc.c
@@ -1162,14 +1162,17 @@ struct page **io_pin_pages(unsigned long ubuf, unsigned long len, int *npages)
 	pret = pin_user_pages(ubuf, nr_pages, FOLL_WRITE | FOLL_LONGTERM,
 			      pages, vmas);
 	if (pret == nr_pages) {
+		struct file *file = vmas[0]->vm_file;
+
 		/* don't support file backed memory */
 		for (i = 0; i < nr_pages; i++) {
-			struct vm_area_struct *vma = vmas[i];
-
-			if (vma_is_shmem(vma))
+			if (vmas[i]->vm_file != file) {
+				ret = -EINVAL;
+				break;
+			}
+			if (!file)
 				continue;
-			if (vma->vm_file &&
-			    !is_file_hugepages(vma->vm_file)) {
+			if (!vma_is_shmem(vmas[i]) && !is_file_hugepages(file)) {
 				ret = -EOPNOTSUPP;
 				break;
 			}
-- 
2.39.1