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>

1 files changed, 53 insertions, 10 deletions

diff --git a/fs/namei.c b/fs/namei.c
index 9e7b18a8be66..a3431639e166 100644
--- 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,