1 files changed, 32 insertions, 1 deletions

diff --git a/fs/configfs/symlink.c b/fs/configfs/symlink.c
index 91eac6c55e07..f3881e4caedd 100644
--- a/fs/configfs/symlink.c
+++ b/fs/configfs/symlink.c
@@ -143,11 +143,42 @@ int configfs_symlink(struct inode *dir, struct dentry *dentry, const char *symna
 	    !type->ct_item_ops->allow_link)
 		goto out_put;
 
+	/*
+	 * This is really sick.  What they wanted was a hybrid of
+	 * link(2) and symlink(2) - they wanted the target resolved
+	 * at syscall time (as link(2) would've done), be a directory
+	 * (which link(2) would've refused to do) *AND* be a deep
+	 * fucking magic, making the target busy from rmdir POV.
+	 * symlink(2) is nothing of that sort, and the locking it
+	 * gets matches the normal symlink(2) semantics.  Without
+	 * attempts to resolve the target (which might very well
+	 * not even exist yet) done prior to locking the parent
+	 * directory.  This perversion, OTOH, needs to resolve
+	 * the target, which would lead to obvious deadlocks if
+	 * attempted with any directories locked.
+	 *
+	 * Unfortunately, that garbage is userland ABI and we should've
+	 * said "no" back in 2005.  Too late now, so we get to
+	 * play very ugly games with locking.
+	 *
+	 * Try *ANYTHING* of that sort in new code, and you will
+	 * really regret it.  Just ask yourself - what could a BOFH
+	 * do to me and do I want to find it out first-hand?
+	 *
+	 *  AV, a thoroughly annoyed bastard.
+	 */
+	inode_unlock(dir);
 	ret = get_target(symname, &path, &target_item, dentry->d_sb);
+	inode_lock(dir);
 	if (ret)
 		goto out_put;
 
-	ret = type->ct_item_ops->allow_link(parent_item, target_item);
+	if (dentry->d_inode || d_unhashed(dentry))
+		ret = -EEXIST;
+	else
+		ret = inode_permission(dir, MAY_WRITE | MAY_EXEC);
+	if (!ret)
+		ret = type->ct_item_ops->allow_link(parent_item, target_item);
 	if (!ret) {
 		mutex_lock(&configfs_symlink_mutex);
 		ret = create_link(parent_item, target_item, dentry);