[patch 08/18] pagemap: require aligned-length, non-null reads of /proc/pid/pagemap

[Greg KH]

2.6.27-stable review patch.  If anyone has any objections, please let us know.

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

From: Vitaly Mayatskikh <v.mayatskih@xxxxxxxxx>

commit 0816178638c15ce5472d39d771a96860dff4141a upstream.

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@xxxxxxxxx>
Cc: Thomas Tuttle <ttuttle@xxxxxxxxxx>
Acked-by: Matt Mackall <mpm@xxxxxxxxxxx>
Cc: Alexey Dobriyan <adobriyan@xxxxxxxxx>
Cc: <stable@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxx>

---
 fs/proc/task_mmu.c |    4 ++++
 1 file changed, 4 insertions(+)

--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -665,6 +665,10 @@ static ssize_t pagemap_read(struct file 
 		goto out_task;
 
 	ret = 0;
+
+	if (!count)
+		goto out_task;
+
 	mm = get_task_mm(task);
 	if (!mm)
 		goto out_task;


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