[ 3.5.y.z extended stable ] Patch "nfs: don't zero out the rest of the page if we hit the EOF" has been added to staging queue

[Herton Ronaldo Krzesinski]

This is a note to let you know that I have just added a patch titled

    nfs: don't zero out the rest of the page if we hit the EOF

to the linux-3.5.y-queue branch of the 3.5.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.5.y-queue

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.5.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Herton

------

>From 32a72be9dab96ff67937c977e21696a9075bb678 Mon Sep 17 00:00:00 2001
From: Jeff Layton <jlayton at redhat.com>
Date: Wed, 12 Dec 2012 11:38:44 -0500
Subject: [PATCH] nfs: don't zero out the rest of the page if we hit the EOF
 on a DIO READ

commit 67fad106a219e083c91c79695bd1807dde1bf7b9 upstream.

Eryu provided a test program that would segfault when attempting to read
past the EOF on file that was opened O_DIRECT. The buffer given to the
read() call was on the stack, and when he attempted to read past it it
would scribble over the rest of the stack page.

If we hit the end of the file on a DIO READ request, then we don't want
to zero out the rest of the buffer. These aren't pagecache pages after
all, and there's no guarantee that the buffers that were passed in
represent entire pages.

Cc: Fred Isaman <iisaman at netapp.com>
Reported-by: Eryu Guan <eguan at redhat.com>
Signed-off-by: Jeff Layton <jlayton at redhat.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust at netapp.com>
Signed-off-by: Herton Ronaldo Krzesinski <herton.krzesinski at canonical.com>
---
 fs/nfs/direct.c |    8 --------
 1 file changed, 8 deletions(-)

diff --git a/fs/nfs/direct.c b/fs/nfs/direct.c
index 4825337..36b3958 100644
--- a/fs/nfs/direct.c
+++ b/fs/nfs/direct.c
@@ -247,14 +247,6 @@ static void nfs_direct_read_completion(struct nfs_pgio_header *hdr)
 		struct nfs_page *req = nfs_list_entry(hdr->pages.next);
 		struct page *page = req->wb_page;

-		if (test_bit(NFS_IOHDR_EOF, &hdr->flags)) {
-			if (bytes > hdr->good_bytes)
-				zero_user(page, 0, PAGE_SIZE);
-			else if (hdr->good_bytes - bytes < PAGE_SIZE)
-				zero_user_segment(page,
-					hdr->good_bytes & ~PAGE_MASK,
-					PAGE_SIZE);
-		}
 		if (!PageCompound(page)) {
 			if (test_bit(NFS_IOHDR_ERROR, &hdr->flags)) {
 				if (bytes < hdr->good_bytes)
--
1.7.9.5