From: Tao Ma Subject: Re: [PATCH] ext4: Save and restore state flags in EXT4_IOC_SETFLAGS. Date: Mon, 04 Jun 2012 11:22:55 +0800 Message-ID: <4FCC2A0F.40804@tao.ma> References: <1336145869-4120-1-git-send-email-tm@tao.ma> <20120601034820.GC7897@thunk.org> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Cc: linux-ext4@vger.kernel.org, stable To: Ted Ts'o Return-path: Received: from oproxy7-pub.bluehost.com ([67.222.55.9]:43262 "HELO oproxy7-pub.bluehost.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1755683Ab2FDDXL (ORCPT ); Sun, 3 Jun 2012 23:23:11 -0400 In-Reply-To: <20120601034820.GC7897@thunk.org> Sender: linux-ext4-owner@vger.kernel.org List-ID: Hi Ted, Sorry for the delay. On 06/01/2012 11:48 AM, Ted Ts'o wrote: > On Fri, May 04, 2012 at 11:37:49PM +0800, Tao Ma wrote: >> From: Tao Ma >> >> In commit 353eb83c we removes i_state_flags with 64-bit longs, >> But in case we call EXT4_IOC_SETFLAGS, we fail to save the >> high 32-bit state flags and only stores the low 32-bit back >> to ei->i_flags. So the state flags are missing now in 64-bit >> long architecture. > > The problem with this approach is that we are still editing i_flags > and then replacing it with the new value. So we're vulnerable to > races where some other process is modifies the i_state_flags between > when we sample it using ext4_save_state_flags() and when we restore > them. > > This is a better way to fix the problem, and what I plan to commit > into the ext4 tree: > > commit 79906964a187c405db72a3abc60eb9b50d804fbc > Author: Theodore Ts'o > Date: Thu May 31 23:46:01 2012 -0400 > > ext4: don't trash state flags in EXT4_IOC_SETFLAGS > > In commit 353eb83c we removed i_state_flags with 64-bit longs, But > when handling the EXT4_IOC_SETFLAGS ioctl, we replace i_flags > directly, which trashes the state flags which are stored in the high > 32-bits of i_flags on 64-bit platforms. So use the the > ext4_{set,clear}_inode_flags() functions which use atomic bit > manipulation functions instead. > > Reported-by: Tao Ma > Signed-off-by: "Theodore Ts'o" > Cc: stable@kernel.org > > diff --git a/fs/ext4/ioctl.c b/fs/ext4/ioctl.c > index feba55a..8ad112a 100644 > --- a/fs/ext4/ioctl.c > +++ b/fs/ext4/ioctl.c > @@ -38,7 +38,7 @@ long ext4_ioctl(struct file *filp, unsigned int cmd, unsigned long arg) > handle_t *handle = NULL; > int err, migrate = 0; > struct ext4_iloc iloc; > - unsigned int oldflags; > + unsigned int oldflags, mask, i; > unsigned int jflag; > > if (!inode_owner_or_capable(inode)) > @@ -115,8 +115,14 @@ long ext4_ioctl(struct file *filp, unsigned int cmd, unsigned long arg) > if (err) > goto flags_err; > > - flags = flags & EXT4_FL_USER_MODIFIABLE; > - flags |= oldflags & ~EXT4_FL_USER_MODIFIABLE; > + for (i = 0, mask = 1; i < 32; i++, mask <<= 1) { > + if (!(mask & EXT4_FL_USER_MODIFIABLE)) > + continue; > + if (mask & flags) > + ext4_set_inode_flag(inode, i); > + else > + ext4_clear_inode_flag(inode, i); > + } > ei->i_flags = flags; You forget to remove this line and we can still get the problem. I am busy with other stuff and when I got to it, it is already in linus' tree. So I have sent out another patch to remove this line and after that my test case passed. The patch subject is "[PATCH] ext4: Don't set i_flags in EXT4_IOC_SETFLAGS." Thanks Tao > > ext4_set_inode_flags(inode); > > > -- > 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