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>

diff --git a/fs/debugfs/inode.c b/fs/debugfs/inode.c
index 0d23b52..b486169 100644 (file)
--- 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;
 }