Unionfs: unionfs_create needs to revalidate the dentry

We have to read-lock the superblock rwsem, and we have to revalidate the
parent dentry and this one.  A branch-management operation could have taken
place, mid-way through a VFS operation that eventually reaches
unionfs_create().  So we have to ensure consistency, just as we do with the
file operations.

Signed-off-by: Erez Zadok <ezk@cs.sunysb.edu>
Signed-off-by: Josef 'Jeff' Sipek <jsipek@cs.sunysb.edu>

diff --git a/fs/unionfs/inode.c b/fs/unionfs/inode.c
index 6dfc16f29d0eb82cf54d19453dbe07e4c0f44999..edd226f5d2989d6779828abb722c4e54cd45fc07 100644 (file)
--- a/fs/unionfs/inode.c
+++ b/fs/unionfs/inode.c
@@ -28,9 +28,35 @@ static int unionfs_create(struct inode *parent, struct dentry *dentry,
        struct dentry *hidden_parent_dentry = NULL;
        int bindex = 0, bstart;
        char *name = NULL;
-
+       int valid = 0;
+
+       /*
+        * We have to read-lock the superblock rwsem, and we have to
+        * revalidate the parent dentry and this one.  A branch-management
+        * operation could have taken place, mid-way through a VFS operation
+        * that eventually reaches here.  So we have to ensure consistency,
+        * just as we do with the file operations.
+        *
+        * XXX: we may need to do this for all other inode ops that take a
+        * dentry.
+        */
+       unionfs_read_lock(dentry->d_sb);
        unionfs_lock_dentry(dentry);
 
+       unionfs_lock_dentry(dentry->d_parent);
+       valid = __unionfs_d_revalidate_chain(dentry->d_parent, nd);
+       unionfs_unlock_dentry(dentry->d_parent);
+       if (!valid) {
+               err = -ENOENT;  /* same as what real_lookup does */
+               goto out;
+       }
+       valid = __unionfs_d_revalidate_chain(dentry, nd);
+       /*
+        * It's only a bug if this dentry was not negative and couldn't be
+        * revalidated (shouldn't happen).
+        */
+       BUG_ON(!valid && dentry->d_inode);
+
        /* We start out in the leftmost branch. */
        bstart = dbstart(dentry);
        hidden_dentry = unionfs_lower_dentry(dentry);
@@ -184,6 +210,7 @@ out:
        kfree(name);
 
        unionfs_unlock_dentry(dentry);
+       unionfs_read_unlock(dentry->d_sb);
        return err;
 }