Patch "CIFS: Fix splice read for non-cached files" has been added to the 4.9-stable tree

[<gregkh@linuxfoundation.org>]

This is a note to let you know that I've just added the patch titled

    CIFS: Fix splice read for non-cached files

to the 4.9-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     cifs-fix-splice-read-for-non-cached-files.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From 9c25702cee1405099f982894c865c163de7909a8 Mon Sep 17 00:00:00 2001
From: Pavel Shilovsky <pshilov@microsoft.com>
Date: Thu, 19 Jan 2017 13:53:15 -0800
Subject: CIFS: Fix splice read for non-cached files

From: Pavel Shilovsky <pshilov@microsoft.com>

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@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 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;


Patches currently in stable-queue which might be from pshilov@microsoft.com are

queue-4.9/cifs-fix-splice-read-for-non-cached-files.patch