ubifs: make ubifs_[get|set]xattr atomic

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@cn.fujitsu.com>
Signed-off-by: Richard Weinberger <richard@nod.at>

1 files changed, 9 insertions, 3 deletions

diff --git a/fs/ubifs/xattr.c b/fs/ubifs/xattr.c
index 96f3448b6eb4..99364aeed035 100644
--- a/fs/ubifs/xattr.c
+++ b/fs/ubifs/xattr.c
@@ -200,6 +200,7 @@ static int change_xattr(struct ubifs_info *c, struct inode *host,
         int err;
         struct ubifs_inode *host_ui = ubifs_inode(host);
         struct ubifs_inode *ui = ubifs_inode(inode);
+        void *buf = NULL;
         struct ubifs_budget_req req = { .dirtied_ino = 2,
                 .dirtied_ino_d = ALIGN(size, 8) + ALIGN(host_ui->data_len, 8) };
 
@@ -208,14 +209,17 @@ static int change_xattr(struct ubifs_info *c, struct inode *host,
         if (err)
                 return err;
 
-        kfree(ui->data);
-        ui->data = kmemdup(value, size, GFP_NOFS);
-        if (!ui->data) {
+        buf = kmemdup(value, size, GFP_NOFS);
+        if (!buf) {
                 err = -ENOMEM;
                 goto out_free;
         }
+        mutex_lock(&ui->ui_mutex);
+        kfree(ui->data);
+        ui->data = buf;
         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 +413,7 @@ 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 +428,7 @@ 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);