From 0816178638c15ce5472d39d771a96860dff4141a Mon Sep 17 00:00:00 2001
From: Vitaly Mayatskikh <v.mayatskih@gmail.com>
Date: Thu, 30 Apr 2009 15:08:18 -0700
Subject: [PATCH] pagemap: require aligned-length, non-null reads of
 /proc/pid/pagemap

The intention of commit aae8679b0ebcaa92f99c1c3cb0cd651594a43915
("pagemap: fix bug in add_to_pagemap, require aligned-length reads of
/proc/pid/pagemap") was to force reads of /proc/pid/pagemap to be a
multiple of 8 bytes, but now it allows to read 0 bytes, which actually
puts some data to user's buffer.  According to POSIX, if count is zero,
read() should return zero and has no other results.

Signed-off-by: Vitaly Mayatskikh <v.mayatskih@gmail.com>
Cc: Thomas Tuttle <ttuttle@google.com>
Acked-by: Matt Mackall <mpm@selenic.com>
Cc: Alexey Dobriyan <adobriyan@gmail.com>
Cc: <stable@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
---
 fs/proc/task_mmu.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index 39e4ad4..6f61b7c 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -665,6 +665,10 @@ static ssize_t pagemap_read(struct file *file, char __user *buf,
 		goto out_task;
 
 	ret = 0;
+
+	if (!count)
+		goto out_task;
+
 	mm = get_task_mm(task);
 	if (!mm)
 		goto out_task;
-- 
2.7.4