On Fri, May 04, 2012 at 11:37:49PM +0800, Tao Ma wrote:
> From: Tao Ma <boyu.mt@xxxxxxxxxx>
>
> 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 <tytso@xxxxxxx>
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 <boyu.mt@xxxxxxxxxx>
Signed-off-by: "Theodore Ts'o" <tytso@xxxxxxx>
Cc: stable@xxxxxxxxxx
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;
ext4_set_inode_flags(inode);
--
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