From: "Darrick J. Wong" Subject: [PATCH] ext4: Prevent stack overrun in ext4_file_open when recording last known mountpoint Date: Thu, 15 Sep 2011 16:16:45 -0700 Message-ID: <20110915231645.GE12086@tux1.beaverton.ibm.com> Reply-To: djwong@us.ibm.com Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: linux-kernel , linux-ext4 To: "Theodore Ts'o" Return-path: Received: from e6.ny.us.ibm.com ([32.97.182.146]:52293 "EHLO e6.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932690Ab1IOXQv (ORCPT ); Thu, 15 Sep 2011 19:16:51 -0400 Content-Disposition: inline Sender: linux-ext4-owner@vger.kernel.org List-ID: In ext4_file_open, the filesystem records the mountpoint of the first file that is opened after mounting the filesystem. It does this by allocating a 64-byte stack buffer, calling d_path() to grab the mount point through which this file was accessed, and then memcpy()ing 64 bytes into the superblock's s_last_mounted field, starting from the return value of d_path(), which is stored as "cp". However, if cp > buf (which it frequently is since path components are prepended starting at the end of buf) then we can end up copying stack data into the superblock. Writing stack variables into the superblock doesn't sound like a great idea, so use strncpy instead. Signed-off-by: Darrick J. Wong --- fs/ext4/file.c | 4 ++-- 1 files changed, 2 insertions(+), 2 deletions(-) diff --git a/fs/ext4/file.c b/fs/ext4/file.c index e4095e9..67223e0 100644 --- a/fs/ext4/file.c +++ b/fs/ext4/file.c @@ -181,8 +181,8 @@ static int ext4_file_open(struct inode * inode, struct file * filp) path.dentry = mnt->mnt_root; cp = d_path(&path, buf, sizeof(buf)); if (!IS_ERR(cp)) { - memcpy(sbi->s_es->s_last_mounted, cp, - sizeof(sbi->s_es->s_last_mounted)); + strncpy(sbi->s_es->s_last_mounted, cp, + sizeof(sbi->s_es->s_last_mounted)); ext4_mark_super_dirty(sb); } }