linux-kernel - [PATCH 3.16 228/305] tmpfs: don't undo fallocate past its last page

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Message-ID: <lsq.1471110171.844392595@decadent.org.uk>
Date:	Sat, 13 Aug 2016 18:42:51 +0100
From:	Ben Hutchings <ben@...adent.org.uk>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:	akpm@...ux-foundation.org,
	"Linus Torvalds" <torvalds@...ux-foundation.org>,
	"Vlastimil Babka" <vbabka@...e.cz>,
	"Anthony Romano" <anthony.romano@...eos.com>,
	"Hugh Dickins" <hughd@...gle.com>,
	"Brandon Philips" <brandon@...p.co>
Subject: [PATCH 3.16 228/305] tmpfs: don't undo fallocate past its last page

3.16.37-rc1 review patch.  If anyone has any objections, please let me know.

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

From: Anthony Romano <anthony.romano@...eos.com>

commit b9b4bb26af017dbe930cd4df7f9b2fc3a0497bfe upstream.

When fallocate is interrupted it will undo a range that extends one byte
past its range of allocated pages.  This can corrupt an in-use page by
zeroing out its first byte.  Instead, undo using the inclusive byte
range.

Fixes: 1635f6a74152f1d ("tmpfs: undo fallocation on failure")
Link: http://lkml.kernel.org/r/1462713387-16724-1-git-send-email-anthony.romano@coreos.com
Signed-off-by: Anthony Romano <anthony.romano@...eos.com>
Cc: Vlastimil Babka <vbabka@...e.cz>
Cc: Hugh Dickins <hughd@...gle.com>
Cc: Brandon Philips <brandon@...p.co>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
[bwh: Backported to 3.16: use PAGE_CACHE_SHIFT instead of PAGE_SHIFT]
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 mm/shmem.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -1867,7 +1867,7 @@ static long shmem_fallocate(struct file
 			/* Remove the !PageUptodate pages we added */
 			shmem_undo_range(inode,
 				(loff_t)start << PAGE_CACHE_SHIFT,
-				(loff_t)index << PAGE_CACHE_SHIFT, true);
+				((loff_t)index << PAGE_CACHE_SHIFT) - 1, true);
 			goto undone;
 		}