[PATCH v3] ubifs: make ubifs_[get|set]xattr atomic

[Dongsheng Yang]

This commit make the ubifs_[get|set]xattr protected by ui_mutex.

Originally, there is a possibility that ubifs_getxattr to get
a wrong value.

  P1                                  P2
----------                  	----------
ubifs_getxattr                      ubifs_setxattr
					- kfree()
- memcpy()
					- kmemdup()

Then ubifs_getxattr() would get a non-sense data. To solve this
problem, this commit make the xattr of ubifs_inode updated in
atomic.

Signed-off-by: Dongsheng Yang <yangds.fnst at cn.fujitsu.com>
---
	-v2
		fix a dead lock in error flow
 fs/ubifs/xattr.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/fs/ubifs/xattr.c b/fs/ubifs/xattr.c
index 96f3448..33badeb 100644
--- a/fs/ubifs/xattr.c
+++ b/fs/ubifs/xattr.c
@@ -208,14 +208,17 @@ static int change_xattr(struct ubifs_info *c, struct inode *host,
 	if (err)
 		return err;
 
+	mutex_lock(&ui->ui_mutex);
 	kfree(ui->data);
 	ui->data = kmemdup(value, size, GFP_NOFS);
 	if (!ui->data) {
+		mutex_unlock(&ui->ui_mutex);
 		err = -ENOMEM;
 		goto out_free;
 	}
 	inode->i_size = ui->ui_size = size;
 	ui->data_len = size;
+	mutex_unlock(&ui->ui_mutex);
 
 	mutex_lock(&host_ui->ui_mutex);
 	host->i_ctime = ubifs_current_time(host);
@@ -409,6 +412,7 @@ ssize_t ubifs_getxattr(struct dentry *dentry, const char *name, void *buf,
 	ubifs_assert(inode->i_size == ui->data_len);
 	ubifs_assert(ubifs_inode(host)->xattr_size > ui->data_len);
 
+	mutex_lock(&ui->ui_mutex);
 	if (buf) {
 		/* If @buf is %NULL we are supposed to return the length */
 		if (ui->data_len > size) {
@@ -423,6 +427,7 @@ ssize_t ubifs_getxattr(struct dentry *dentry, const char *name, void *buf,
 	err = ui->data_len;
 
 out_iput:
+	mutex_unlock(&ui->ui_mutex);
 	iput(inode);
 out_unlock:
 	kfree(xent);
-- 
1.8.4.2