vfs: introduce d_instantiate_no_diralias()
...which just returns -EBUSY if a directory alias would be created.
This is to be used by fuse mkdir to make sure that a buggy or malicious
userspace filesystem doesn't do anything nasty. Previously fuse used a
private mutex for this purpose, which can now go away.
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
diff --git a/fs/dcache.c b/fs/dcache.c
index d888223..c8e83d0 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -1801,6 +1801,33 @@
EXPORT_SYMBOL(d_instantiate_unique);
+/**
+ * d_instantiate_no_diralias - instantiate a non-aliased dentry
+ * @entry: dentry to complete
+ * @inode: inode to attach to this dentry
+ *
+ * Fill in inode information in the entry. If a directory alias is found, then
+ * return an error (and drop inode). Together with d_materialise_unique() this
+ * guarantees that a directory inode may never have more than one alias.
+ */
+int d_instantiate_no_diralias(struct dentry *entry, struct inode *inode)
+{
+ BUG_ON(!hlist_unhashed(&entry->d_alias));
+
+ spin_lock(&inode->i_lock);
+ if (S_ISDIR(inode->i_mode) && !hlist_empty(&inode->i_dentry)) {
+ spin_unlock(&inode->i_lock);
+ iput(inode);
+ return -EBUSY;
+ }
+ __d_instantiate(entry, inode);
+ spin_unlock(&inode->i_lock);
+ security_d_instantiate(entry, inode);
+
+ return 0;
+}
+EXPORT_SYMBOL(d_instantiate_no_diralias);
+
struct dentry *d_make_root(struct inode *root_inode)
{
struct dentry *res = NULL;