From: "Darrick J. Wong" Subject: [PATCH 4/5] ext4: Prevent stack overrun in ext4_file_open when recording last known mountpoint Date: Fri, 21 Oct 2011 14:18:18 -0700 Message-ID: <20111021211818.10784.77127.stgit@elm3c44.beaverton.ibm.com> References: <20111021211759.10784.17257.stgit@elm3c44.beaverton.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Cc: linux-ext4@vger.kernel.org, linux-kernel To: Tao Ma , Theodore Tso Return-path: Received: from e36.co.us.ibm.com ([32.97.110.154]:57451 "EHLO e36.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752461Ab1JUVSY (ORCPT ); Fri, 21 Oct 2011 17:18:24 -0400 Received: from /spool/local by e36.co.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Fri, 21 Oct 2011 15:18:24 -0600 In-Reply-To: <20111021211759.10784.17257.stgit@elm3c44.beaverton.ibm.com> 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 strlcpy instead. Andi Kleen suggested using strlcpy instead of strncpy. 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..9781099 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)); + strlcpy(sbi->s_es->s_last_mounted, cp, + sizeof(sbi->s_es->s_last_mounted)); ext4_mark_super_dirty(sb); } }