From mboxrd@z Thu Jan  1 00:00:00 1970
From: Wu Fengguang <fengguang.wu@intel.com>
Subject: [PATCH 5/5] devmem: dont allow seek to last page
Date: Sat, 30 Jan 2010 17:45:20 +0800
Message-ID: <20100130094958.141191239@intel.com>
References: <20100130094515.475881280@intel.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>,
	LKML <linux-kernel@vger.kernel.org>,
	OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
To: Andrew Morton <akpm@linux-foundation.org>
Return-path: <linux-kernel-owner+glk-linux-kernel-3=40m.gmane.org-S1753502Ab0A3JyX@vger.kernel.org>
cc: Al Viro <viro@ZenIV.linux.org.uk>
cc: <linux-fsdevel@vger.kernel.org>
Content-Disposition: inline; filename=mem-seek-fix
Sender: linux-kernel-owner@vger.kernel.org
List-Id: linux-fsdevel.vger.kernel.org

So as to return a uniform error -EOVERFLOW instead of a random one:

# kmem-seek 0xfffffffffffffff0
seek /dev/kmem: Device or resource busy
# kmem-seek 0xfffffffffffffff1
seek /dev/kmem: Block device required

Suggested by OGAWA Hirofumi.

CC: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
---
 drivers/char/mem.c |   19 +++++++++++++------
 1 file changed, 13 insertions(+), 6 deletions(-)

--- linux-mm.orig/drivers/char/mem.c	2010-01-30 17:41:51.000000000 +0800
+++ linux-mm/drivers/char/mem.c	2010-01-30 17:42:29.000000000 +0800
@@ -721,16 +721,23 @@ static loff_t memory_lseek(struct file *
 
 	mutex_lock(&file->f_path.dentry->d_inode->i_mutex);
 	switch (orig) {
-		case 0:
+		case SEEK_CUR:
+			offset += file->f_pos;
+			if ((unsigned long long)offset <
+			    (unsigned long long)file->f_pos) {
+				ret = -EOVERFLOW;
+				break;
+			}
+		case SEEK_SET:
+			/* to avoid userland mistaking f_pos=-9 as -EBADF=-9 */
+			if ((unsigned long long)offset >= ~0xFFFULL) {
+				ret = -EOVERFLOW;
+				break;
+			}
 			file->f_pos = offset;
 			ret = file->f_pos;
 			force_successful_syscall_return();
 			break;
-		case 1:
-			file->f_pos += offset;
-			ret = file->f_pos;
-			force_successful_syscall_return();
-			break;
 		default:
 			ret = -EINVAL;
 	}