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 <[email protected]>
>>
>> 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 <[email protected]>
> 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 <[email protected]>
> Signed-off-by: "Theodore Ts'o" <[email protected]>
> Cc: [email protected]
>
> 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);
>
>
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