debugfs: fix create mutex racy fops and private data

Setting fops and private data outside of the mutex at debugfs file
creation introduces a race where the files can be opened with the wrong
file operations and private data.  It is easy to trigger with a process
waiting on file creation notification.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Cc: stable <stable@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

1 files changed, 32 insertions, 23 deletions

diff --git a/fs/debugfs/inode.c b/fs/debugfs/inode.c
index 0d23b52dd22c..b486169f42bf 100644
--- a/fs/debugfs/inode.c
+++ b/fs/debugfs/inode.c
@@ -32,7 +32,9 @@ static struct vfsmount *debugfs_mount;
 static int debugfs_mount_count;
 static bool debugfs_registered;
 
-static struct inode *debugfs_get_inode(struct super_block *sb, int mode, dev_t dev)
+static struct inode *debugfs_get_inode(struct super_block *sb, int mode, dev_t dev,
+                                       void *data, const struct file_operations *fops)
+
 {
         struct inode *inode = new_inode(sb);
 
@@ -44,14 +46,18 @@ static struct inode *debugfs_get_inode(struct super_block *sb, int mode, dev_t d
                         init_special_inode(inode, mode, dev);
                         break;
                 case S_IFREG:
-                        inode->i_fop = &debugfs_file_operations;
+                        inode->i_fop = fops ? fops : &debugfs_file_operations;
+                        inode->i_private = data;
                         break;
                 case S_IFLNK:
                         inode->i_op = &debugfs_link_operations;
+                        inode->i_fop = fops;
+                        inode->i_private = data;
                         break;
                 case S_IFDIR:
                         inode->i_op = &simple_dir_inode_operations;
-                        inode->i_fop = &simple_dir_operations;
+                        inode->i_fop = fops ? fops : &simple_dir_operations;
+                        inode->i_private = data;
 
                         /* directory inodes start off with i_nlink == 2
                          * (for "." entry) */
@@ -64,7 +70,8 @@ static struct inode *debugfs_get_inode(struct super_block *sb, int mode, dev_t d
 
 /* SMP-safe */
 static int debugfs_mknod(struct inode *dir, struct dentry *dentry,
-                         int mode, dev_t dev)
+                         int mode, dev_t dev, void *data,
+                         const struct file_operations *fops)
 {
         struct inode *inode;
         int error = -EPERM;
@@ -72,7 +79,7 @@ static int debugfs_mknod(struct inode *dir, struct dentry *dentry,
         if (dentry->d_inode)
                 return -EEXIST;
 
-        inode = debugfs_get_inode(dir->i_sb, mode, dev);
+        inode = debugfs_get_inode(dir->i_sb, mode, dev, data, fops);
         if (inode) {
                 d_instantiate(dentry, inode);
                 dget(dentry);
@@ -81,12 +88,13 @@ static int debugfs_mknod(struct inode *dir, struct dentry *dentry,
         return error;
 }
 
-static int debugfs_mkdir(struct inode *dir, struct dentry *dentry, int mode)
+static int debugfs_mkdir(struct inode *dir, struct dentry *dentry, int mode,
+                         void *data, const struct file_operations *fops)
 {
         int res;
 
         mode = (mode & (S_IRWXUGO | S_ISVTX)) | S_IFDIR;
-        res = debugfs_mknod(dir, dentry, mode, 0);
+        res = debugfs_mknod(dir, dentry, mode, 0, data, fops);
         if (!res) {
                 inc_nlink(dir);
                 fsnotify_mkdir(dir, dentry);
@@ -94,18 +102,20 @@ static int debugfs_mkdir(struct inode *dir, struct dentry *dentry, int mode)
         return res;
 }
 
-static int debugfs_link(struct inode *dir, struct dentry *dentry, int mode)
+static int debugfs_link(struct inode *dir, struct dentry *dentry, int mode,
+                        void *data, const struct file_operations *fops)
 {
         mode = (mode & S_IALLUGO) | S_IFLNK;
-        return debugfs_mknod(dir, dentry, mode, 0);
+        return debugfs_mknod(dir, dentry, mode, 0, data, fops);
 }
 
-static int debugfs_create(struct inode *dir, struct dentry *dentry, int mode)
+static int debugfs_create(struct inode *dir, struct dentry *dentry, int mode,
+                          void *data, const struct file_operations *fops)
 {
         int res;
 
         mode = (mode & S_IALLUGO) | S_IFREG;
-        res = debugfs_mknod(dir, dentry, mode, 0);
+        res = debugfs_mknod(dir, dentry, mode, 0, data, fops);
         if (!res)
                 fsnotify_create(dir, dentry);
         return res;
@@ -139,7 +149,9 @@ static struct file_system_type debug_fs_type = {
 
 static int debugfs_create_by_name(const char *name, mode_t mode,
                                   struct dentry *parent,
-                                  struct dentry **dentry)
+                                  struct dentry **dentry,
+                                  void *data,
+                                  const struct file_operations *fops)
 {
         int error = 0;
 
@@ -164,13 +176,16 @@ static int debugfs_create_by_name(const char *name, mode_t mode,
         if (!IS_ERR(*dentry)) {
                 switch (mode & S_IFMT) {
                 case S_IFDIR:
-                        error = debugfs_mkdir(parent->d_inode, *dentry, mode);
+                        error = debugfs_mkdir(parent->d_inode, *dentry, mode,
+                                              data, fops);
                         break;
                 case S_IFLNK:
-                        error = debugfs_link(parent->d_inode, *dentry, mode);
+                        error = debugfs_link(parent->d_inode, *dentry, mode,
+                                             data, fops);
                         break;
                 default:
-                        error = debugfs_create(parent->d_inode, *dentry, mode);
+                        error = debugfs_create(parent->d_inode, *dentry, mode,
+                                               data, fops);
                         break;
                 }
                 dput(*dentry);
@@ -221,19 +236,13 @@ struct dentry *debugfs_create_file(const char *name, mode_t mode,
         if (error)
                 goto exit;
 
-        error = debugfs_create_by_name(name, mode, parent, &dentry);
+        error = debugfs_create_by_name(name, mode, parent, &dentry,
+                                       data, fops);
         if (error) {
                 dentry = NULL;
                 simple_release_fs(&debugfs_mount, &debugfs_mount_count);
                 goto exit;
         }
-
-        if (dentry->d_inode) {
-                if (data)
-                        dentry->d_inode->i_private = data;
-                if (fops)
-                        dentry->d_inode->i_fop = fops;
-        }
 exit:
         return dentry;
 }