Make trailing symlink resolution in path_lookupat() iterative

Now the only caller of link_path_walk() that does *not* pass
LOOKUP_PARENT is do_follow_link()

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

diff --git a/fs/namei.c b/fs/namei.c
index 9e7b18a8be66e4f6c3d4c96b4db8c7500319259a..a3431639e166dbd766c0f9eb70c82530aec0110f 100644 (file)
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -1588,12 +1588,23 @@ out_fail:
        return retval;
 }
 
+static inline int lookup_last(struct nameidata *nd, struct path *path)
+{
+       if (nd->last_type == LAST_NORM && nd->last.name[nd->last.len])
+               nd->flags |= LOOKUP_FOLLOW | LOOKUP_DIRECTORY;
+
+       nd->flags &= ~LOOKUP_PARENT;
+       return walk_component(nd, path, &nd->last, nd->last_type,
+                                       nd->flags & LOOKUP_FOLLOW);
+}
+
 /* Returns 0 and nd will be valid on success; Retuns error, otherwise. */
 static int path_lookupat(int dfd, const char *name,
                                unsigned int flags, struct nameidata *nd)
 {
        struct file *base = NULL;
-       int retval;
+       struct path path;
+       int err;
 
        /*
         * Path walking is largely split up into 2 different synchronisation
@@ -1609,23 +1620,55 @@ static int path_lookupat(int dfd, const char *name,
         * be handled by restarting a traditional ref-walk (which will always
         * be able to complete).
         */
-       retval = path_init(dfd, name, flags, nd, &base);
+       err = path_init(dfd, name, flags | LOOKUP_PARENT, nd, &base);
 
-       if (unlikely(retval))
-               return retval;
+       if (unlikely(err))
+               return err;
 
        current->total_link_count = 0;
-       retval = link_path_walk(name, nd);
+       err = link_path_walk(name, nd);
+
+       if (!err && !(flags & LOOKUP_PARENT)) {
+               int count = 0;
+               err = lookup_last(nd, &path);
+               while (err > 0) {
+                       void *cookie;
+                       struct path link = path;
+                       struct inode *inode = link.dentry->d_inode;
+
+                       if (count++ > 32) {
+                               path_put_conditional(&path, nd);
+                               path_put(&nd->path);
+                               err = -ELOOP;
+                               break;
+                       }
+                       cond_resched();
+                       nd->flags |= LOOKUP_PARENT;
+                       err = __do_follow_link(&link, nd, &cookie);
+                       if (!err)
+                               err = lookup_last(nd, &path);
+                       if (!IS_ERR(cookie) && inode->i_op->put_link)
+                               inode->i_op->put_link(link.dentry, nd, cookie);
+                       path_put(&link);
+               }
+       }
 
        if (nd->flags & LOOKUP_RCU) {
                /* went all way through without dropping RCU */
-               BUG_ON(retval);
+               BUG_ON(err);
                if (nameidata_drop_rcu_last(nd))
-                       retval = -ECHILD;
+                       err = -ECHILD;
        }
 
-       if (!retval)
-               retval = handle_reval_path(nd);
+       if (!err)
+               err = handle_reval_path(nd);
+
+       if (!err && nd->flags & LOOKUP_DIRECTORY) {
+               if (!nd->inode->i_op->lookup) {
+                       path_put(&nd->path);
+                       return -ENOTDIR;
+               }
+       }
 
        if (base)
                fput(base);
@@ -1634,7 +1677,7 @@ static int path_lookupat(int dfd, const char *name,
                path_put(&nd->root);
                nd->root.mnt = NULL;
        }
-       return retval;
+       return err;
 }
 
 static int do_path_lookup(int dfd, const char *name,