Re: [RFC][PATCH v2] ext4: add expose_stale_data flag in fallocate
From: Ric Wheeler
Date: Thu May 03 2012 - 06:10:05 EST
On 05/03/2012 12:14 AM, Zheng Liu wrote:
Hi all,
Here is the v2 of FALLOC_FL_NO_HIDE_STALE in fallocate. Now no new flag is
added into vfs in order to reduce the impacts and avoid a huge security hole.
The application cannot call fallocate with a new flag to create an unwritten
extent. It needs to call ioctl to enable/disable this feature. Meanwhile, in
ioctl, filesystem will check CAP_SYS_RAWIO to ensure that the user has a
privilege to switch on/off it. Currently, I only implement it in ext4.
Hi Zheng,
I thought that we had pretty much decided to try and fix the ext4 performance
impact, not pursue this?
Thanks!
Ric
Even though I try to reduce its impact, this feature still brings a security
hole. So the application must ensure that it initializes an unwritten extent
by itself before reading it, and it is used in a limited environment.
v1 -> v2:
* remove FALLOC_FL_NO_HIDE_STALE flag in vfs
* add 'i_expose_stale_data' in ext4 to enable/disable it
Regards,
Zheng
From 530045b4a1f75df5afd40c0e20c89917f97d7d5a Mon Sep 17 00:00:00 2001
From: Zheng Liu<wenqing.lz@xxxxxxxxxx>
Date: Thu, 3 May 2012 11:21:44 +0800
Subject: [RFC][PATCH v2] ext4: add expose_stale_data flag in fallocate
We can use fallocate to preallocate sequential blocks. But these extents are
uninitialized. So when the application does a write, filesystem will
initialized these unwritten extents and it brings a huge overhead in some
cases.
This patch adds a new flag in inode to indicate whether initialize an unwritten
extent or not. This flag is enable/disable within ioctl that switch on/off this
feature. The application must call ioctl to enable this feature before it tries
to preallocate some blocks.
Obviously, this feature brings a huge security hole. The application must
guarantee to initialize this file by itself before reading it at the same
offset. So the application *MUST* use it carefully.
CC: Ric Wheeler<rwheeler@xxxxxxxxxx>
CC: Eric Sandeen<sandeen@xxxxxxxxxx>
CC: Ted Ts'o tytso@xxxxxxx>
CC: Dave Chinner<david@xxxxxxxxxxxxx>
CC: Lukas Czerner<lczerner@xxxxxxxxxx>
CC: Andreas Dilger<adilger@xxxxxxxxxxxxx>
CC: Szabolcs Szakacsits<szaka@xxxxxxxxxx>
Signed-off-by: Zheng Liu<wenqing.lz@xxxxxxxxxx>
---
fs/ext4/ext4.h | 5 +++++
fs/ext4/extents.c | 6 +++++-
fs/ext4/ioctl.c | 43 +++++++++++++++++++++++++++++++++++++++++++
fs/ext4/super.c | 1 +
4 files changed, 54 insertions(+), 1 deletions(-)
diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index 0e01e90..f56caf0 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -593,6 +593,8 @@ enum {
#define EXT4_IOC_ALLOC_DA_BLKS _IO('f', 12)
#define EXT4_IOC_MOVE_EXT _IOWR('f', 15, struct move_extent)
#define EXT4_IOC_RESIZE_FS _IOW('f', 16, __u64)
+#define EXT4_IOC_GET_EXPOSE_STALE _IOR('f', 17, int)
+#define EXT4_IOC_SET_EXPOSE_STALE _IOW('f', 18, int)
#if defined(__KERNEL__)&& defined(CONFIG_COMPAT)
/*
@@ -908,6 +910,9 @@ struct ext4_inode_info {
*/
tid_t i_sync_tid;
tid_t i_datasync_tid;
+
+ /* expose stale data in creating a new extent */
+ int i_expose_stale_data;
};
/*
diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
index abcdeab..14f54f1 100644
--- a/fs/ext4/extents.c
+++ b/fs/ext4/extents.c
@@ -4269,6 +4269,7 @@ static void ext4_falloc_update_inode(struct inode *inode,
long ext4_fallocate(struct file *file, int mode, loff_t offset, loff_t len)
{
struct inode *inode = file->f_path.dentry->d_inode;
+ struct ext4_inode_info *ei = EXT4_I(inode);
handle_t *handle;
loff_t new_size;
unsigned int max_blocks;
@@ -4312,7 +4313,10 @@ long ext4_fallocate(struct file *file, int mode, loff_t offset, loff_t len)
trace_ext4_fallocate_exit(inode, offset, max_blocks, ret);
return ret;
}
- flags = EXT4_GET_BLOCKS_CREATE_UNINIT_EXT;
+ if (ei->i_expose_stale_data)
+ flags = EXT4_GET_BLOCKS_CREATE;
+ else
+ flags = EXT4_GET_BLOCKS_CREATE_UNINIT_EXT;
if (mode& FALLOC_FL_KEEP_SIZE)
flags |= EXT4_GET_BLOCKS_KEEP_SIZE;
/*
diff --git a/fs/ext4/ioctl.c b/fs/ext4/ioctl.c
index 6eee255..a37db8e 100644
--- a/fs/ext4/ioctl.c
+++ b/fs/ext4/ioctl.c
@@ -432,6 +432,47 @@ resizefs_out:
return 0;
}
+ case EXT4_IOC_GET_EXPOSE_STALE: {
+ int enable;
+
+ /* security check */
+ if (!capable(CAP_SYS_RAWIO))
+ return -EPERM;
+
+ /*
+ * currently only extent-based files support (pre)allocate with
+ * EXPOSE_STALE_DATA flag
+ */
+ if (!(ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS)))
+ return -EOPNOTSUPP;
+
+ enable = ei->i_expose_stale_data;
+
+ return put_user(enable, (int __user *) arg);
+ }
+
+ case EXT4_IOC_SET_EXPOSE_STALE: {
+ int enable;
+
+ /* security check */
+ if (!capable(CAP_SYS_RAWIO))
+ return -EPERM;
+
+ /*
+ * currently only extent-based files support (pre)allocate with
+ * EXPOSE_STALE_DATA flag
+ */
+ if (!(ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS)))
+ return -EOPNOTSUPP;
+
+ if (get_user(enable, (int __user *) arg))
+ return -EFAULT;
+
+ ei->i_expose_stale_data = enable;
+
+ return 0;
+ }
+
default:
return -ENOTTY;
}
@@ -495,6 +536,8 @@ long ext4_compat_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
case EXT4_IOC_MOVE_EXT:
case FITRIM:
case EXT4_IOC_RESIZE_FS:
+ case EXT4_IOC_GET_EXPOSE_STALE:
+ case EXT4_IOC_SET_EXPOSE_STALE:
break;
default:
return -ENOIOCTLCMD;
diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index e1fb1d5..6de2db0 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -943,6 +943,7 @@ static struct inode *ext4_alloc_inode(struct super_block *sb)
ei->i_datasync_tid = 0;
atomic_set(&ei->i_ioend_count, 0);
atomic_set(&ei->i_aiodio_unwritten, 0);
+ ei->i_expose_stale_data = 0;
return&ei->vfs_inode;
}
--
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