From: "Darrick J. Wong" Subject: Re: [PATCH v2] ext4: Prevent stack overrun in ext4_file_open when recording last known mountpoint Date: Fri, 30 Sep 2011 12:46:55 -0700 Message-ID: <20110930194655.GX12086@tux1.beaverton.ibm.com> References: <20110915231645.GE12086@tux1.beaverton.ibm.com> <20110916184005.GH12086@tux1.beaverton.ibm.com> Reply-To: djwong@us.ibm.com Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: "Theodore Ts'o" , linux-kernel , linux-ext4 To: Andi Kleen Return-path: Received: from e5.ny.us.ibm.com ([32.97.182.145]:41265 "EHLO e5.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755450Ab1I3Tqz (ORCPT ); Fri, 30 Sep 2011 15:46:55 -0400 Content-Disposition: inline In-Reply-To: <20110916184005.GH12086@tux1.beaverton.ibm.com> Sender: linux-ext4-owner@vger.kernel.org List-ID: On Fri, Sep 16, 2011 at 11:40:05AM -0700, Darrick J. Wong wrote: > 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. Ok, it's been a couple of weeks.... any thoughts, Ted? --D > > 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); > } > } > -- > To unsubscribe from this list: send the line "unsubscribe linux-ext4" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html >