debugfs: full_proxy_open(): free proxy on ->open() failure

Debugfs' full_proxy_open(), the ->open() installed at all inodes created
through debugfs_create_file(),
- grabs a reference to the original struct file_operations instance passed
  to debugfs_create_file(),
- dynamically allocates a proxy struct file_operations instance wrapping
  the original
- and installs this at the file's ->f_op.

Afterwards, it calls the original ->open() and passes its return value back
to the VFS layer.

Now, if that return value indicates failure, the VFS layer won't ever call
->release() and thus, neither the reference to the original file_operations
nor the memory for the proxy file_operations will get released, i.e. both
are leaked.

Upon failure of the original fops' ->open(), undo the proxy installation.
That is:
- Set the struct file ->f_op to what it had been when full_proxy_open()
  was entered.
- Drop the reference to the original file_operations.
- Free the memory holding the proxy file_operations.

Fixes: 49d200deaa68 ("debugfs: prevent access to removed files' private
                      data")
Signed-off-by: Nicolai Stange <nicstange@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/fs/debugfs/file.c b/fs/debugfs/file.c
index 9c1c9a0..d1ec803 100644 (file)
--- a/fs/debugfs/file.c
+++ b/fs/debugfs/file.c
@@ -262,8 +262,10 @@ static int full_proxy_open(struct inode *inode, struct file *filp)
 
        if (real_fops->open) {
                r = real_fops->open(inode, filp);
-
-               if (filp->f_op != proxy_fops) {
+               if (r) {
+                       replace_fops(filp, d_inode(dentry)->i_fop);
+                       goto free_proxy;
+               } else if (filp->f_op != proxy_fops) {
                        /* No protection against file removal anymore. */
                        WARN(1, "debugfs file owner replaced proxy fops: %pd",
                                dentry);