Turn resolution of trailing symlinks iterative everywhere
Al Viro [Tue, 15 Mar 2011 01:54:55 +0000 (21:54 -0400)]
The last remaining place (resolution of nested symlink) converted
to the loop of the same kind we have in path_lookupat() and
path_openat().

Note that we still *do* have a recursion in pathname resolution;
can't avoid it, really.  However, it's strictly for nested symlinks
now - i.e. ones in the middle of a pathname.

link_path_walk() has lost the tail now - it always walks everything
except the last component.

do_follow_link() renamed to nested_symlink() and moved down.

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

fs/namei.c

index 9575d00..017c3fa 100644 (file)
@@ -779,40 +779,6 @@ __do_follow_link(const struct path *link, struct nameidata *nd, void **p)
        return error;
 }
 
-/*
- * This limits recursive symlink follows to 8, while
- * limiting consecutive symlinks to 40.
- *
- * Without that kind of total limit, nasty chains of consecutive
- * symlinks can cause almost arbitrarily long lookups. 
- */
-static inline int do_follow_link(struct path *path, struct nameidata *nd)
-{
-       void *cookie;
-       int err = -ELOOP;
-
-       if (current->link_count >= MAX_NESTED_LINKS)
-               goto loop;
-       if (current->total_link_count >= 40)
-               goto loop;
-       BUG_ON(nd->depth >= MAX_NESTED_LINKS);
-       cond_resched();
-       current->link_count++;
-       current->total_link_count++;
-       nd->depth++;
-       err = __do_follow_link(path, nd, &cookie);
-       if (!IS_ERR(cookie) && path->dentry->d_inode->i_op->put_link)
-               path->dentry->d_inode->i_op->put_link(path->dentry, nd, cookie);
-       path_put(path);
-       current->link_count--;
-       nd->depth--;
-       return err;
-loop:
-       path_put_conditional(path, nd);
-       path_put(&nd->path);
-       return err;
-}
-
 static int follow_up_rcu(struct path *path)
 {
        struct vfsmount *parent;
@@ -1367,6 +1333,52 @@ static inline int walk_component(struct nameidata *nd, struct path *path,
 }
 
 /*
+ * This limits recursive symlink follows to 8, while
+ * limiting consecutive symlinks to 40.
+ *
+ * Without that kind of total limit, nasty chains of consecutive
+ * symlinks can cause almost arbitrarily long lookups.
+ */
+static inline int nested_symlink(struct path *path, struct nameidata *nd)
+{
+       int res;
+
+       BUG_ON(nd->depth >= MAX_NESTED_LINKS);
+       if (unlikely(current->link_count >= MAX_NESTED_LINKS)) {
+               path_put_conditional(path, nd);
+               path_put(&nd->path);
+               return -ELOOP;
+       }
+
+       nd->depth++;
+       current->link_count++;
+
+       do {
+               struct path link = *path;
+               void *cookie;
+               if (unlikely(current->total_link_count >= 40)) {
+                       path_put_conditional(path, nd);
+                       path_put(&nd->path);
+                       res = -ELOOP;
+                       break;
+               }
+               cond_resched();
+               current->total_link_count++;
+               res = __do_follow_link(&link, nd, &cookie);
+               if (!res)
+                       res = walk_component(nd, path, &nd->last,
+                                            nd->last_type, LOOKUP_FOLLOW);
+               if (!IS_ERR(cookie) && link.dentry->d_inode->i_op->put_link)
+                       link.dentry->d_inode->i_op->put_link(link.dentry, nd, cookie);
+               path_put(&link);
+       } while (res > 0);
+
+       current->link_count--;
+       nd->depth--;
+       return res;
+}
+
+/*
  * Name resolution.
  * This is the basic name resolution function, turning a pathname into
  * the final dentry. We expect 'base' to be positive and a directory.
@@ -1385,9 +1397,6 @@ static int link_path_walk(const char *name, struct nameidata *nd)
        if (!*name)
                return 0;
 
-       if (nd->depth)
-               lookup_flags = LOOKUP_FOLLOW | (nd->flags & LOOKUP_CONTINUE);
-
        /* At this point we know we have a real path component. */
        for(;;) {
                unsigned long hash;
@@ -1440,14 +1449,14 @@ static int link_path_walk(const char *name, struct nameidata *nd)
                        goto last_component;
                while (*++name == '/');
                if (!*name)
-                       goto last_with_slashes;
+                       goto last_component;
 
                err = walk_component(nd, &next, &this, type, LOOKUP_FOLLOW);
                if (err < 0)
                        return err;
 
                if (err) {
-                       err = do_follow_link(&next, nd);
+                       err = nested_symlink(&next, nd);
                        if (err)
                                return err;
                }
@@ -1457,24 +1466,11 @@ static int link_path_walk(const char *name, struct nameidata *nd)
                continue;
                /* here ends the main loop */
 
-last_with_slashes:
-               lookup_flags |= LOOKUP_FOLLOW | LOOKUP_DIRECTORY;
 last_component:
                /* Clear LOOKUP_CONTINUE iff it was previously unset */
                nd->flags &= lookup_flags | ~LOOKUP_CONTINUE;
-               if (lookup_flags & LOOKUP_PARENT) {
-                       nd->last = this;
-                       nd->last_type = type;
-                       return 0;
-               }
-               err = walk_component(nd, &next, &this, type, LOOKUP_FOLLOW);
-               if (err < 0)
-                       return err;
-               if (err) {
-                       err = do_follow_link(&next, nd);
-                       if (err)
-                               return err;
-               }
+               nd->last = this;
+               nd->last_type = type;
                return 0;
        }
        terminate_walk(nd);