[PATCH 2/3] devmem: check vmalloc address on kmem read/write

[Wu Fengguang <fengguang.wu@intel.com>]

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From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>

Otherwise vmalloc_to_page() will BUG().

This also makes the kmem read/write implementation aligned with mem(4):
"References to nonexistent locations cause errors to be returned." Here
we return -ENXIO (inspired by Hugh) if no bytes have been transfered
to/from user space, otherwise return partial read/write results.

CC: Greg Kroah-Hartman <gregkh@suse.de>
CC: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
---
 drivers/char/mem.c |    8 ++++++++
 1 file changed, 8 insertions(+)

--- linux-mm.orig/drivers/char/mem.c	2009-09-16 08:52:17.000000000 +0800
+++ linux-mm/drivers/char/mem.c	2009-09-16 09:15:03.000000000 +0800
@@ -443,6 +443,10 @@ static ssize_t read_kmem(struct file *fi
 			return -ENOMEM;
 		while (count > 0) {
 			sz = size_inside_page(p, count);
+			if (!is_vmalloc_or_module_addr((void *)p)) {
+				err = -ENXIO;
+				break;
+			}
 			err = vread(kbuf, (char *)p, sz);
 			if (err)
 				break;
@@ -543,6 +547,10 @@ static ssize_t write_kmem(struct file * 
 			unsigned long sz = size_inside_page(p, count);
 			unsigned long n;
 
+			if (!is_vmalloc_or_module_addr((void *)p)) {
+				err = -ENXIO;
+				break;
+			}
 			n = copy_from_user(kbuf, buf, sz);
 			if (n) {
 				err = -EFAULT;

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