[PATCH 4.9 041/153] CIFS: Fix splice read for non-cached files

[Greg Kroah-Hartman]

4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Pavel Shilovsky <pshilov@xxxxxxxxxxxxx>

commit 9c25702cee1405099f982894c865c163de7909a8 upstream.

Currently we call copy_page_to_iter() for uncached reading into a pipe.
This is wrong because it treats pages as VFS cache pages and copies references
rather than actual data. When we are trying to read from the pipe we end up
calling page_cache_pipe_buf_confirm() which returns -ENODATA. This error
is translated into 0 which is returned to a user.

This issue is reproduced by running xfs-tests suite (generic test #249)
against mount points with "cache=none". Fix it by mapping pages manually
and calling copy_to_iter() that copies data into the pipe.

Signed-off-by: Pavel Shilovsky <pshilov@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 fs/cifs/file.c |   10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

--- a/fs/cifs/file.c
+++ b/fs/cifs/file.c
@@ -2884,7 +2884,15 @@ cifs_readdata_to_iov(struct cifs_readdat
 	for (i = 0; i < rdata->nr_pages; i++) {
 		struct page *page = rdata->pages[i];
 		size_t copy = min_t(size_t, remaining, PAGE_SIZE);
-		size_t written = copy_page_to_iter(page, 0, copy, iter);
+		size_t written;
+
+		if (unlikely(iter->type & ITER_PIPE)) {
+			void *addr = kmap_atomic(page);
+
+			written = copy_to_iter(addr, copy, iter);
+			kunmap_atomic(addr);
+		} else
+			written = copy_page_to_iter(page, 0, copy, iter);
 		remaining -= written;
 		if (written < copy && iov_iter_count(iter) > 0)
 			break;