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Date: Sat, 20 Apr 2013 15:31:57 +0800
From: Chen Gang <gang.chen@...anux.com>
To: Chen Gang F T <chen.gang.flying.transformer@...il.com>
CC: Andrew Morton <akpm@...ux-foundation.org>,
Eric Paris <eparis@...hat.com>,
Al Viro <viro@...iv.linux.org.uk>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] kernel: audit_tree: resource management: need put_tree
and goto Err when failure occures
On 2013年04月18日 09:19, Chen Gang F T wrote:
> On 2013年04月18日 04:07, Andrew Morton wrote:
>> > On Wed, 17 Apr 2013 12:04:02 +0800 Chen Gang <gang.chen@...anux.com> wrote:
>> >
>>>> >> > since "normally audit_add_tree_rule() will free it on failure",
>>>> >> > need free it completely, when failure occures.
>>>> >> >
>>>> >> > need additional put_tree before return, since get_tree was called.
>>>> >> > always need goto error processing area for list_del_init.
>> > Isn't that get_tree() in audit_add_tree_rule() simply unneeded? In
>> > other words, is this patch correct:
>> >
after reading code again, I think:
we can remove the pair of get_tree() and put_tree(),
a. the author want to pretect tree not to be freed after unlock audit_filter_mutex
when tree is really freed by others, we have chance to check tree->goner
b. it just like another functions done (audit_tag_tree, audit_trim_trees)
for audit_add_tree_rule, also need let get_tree() protected by audit_filter_mutex.
(move 'get_tree' before unlock audit_filter_mutex)
c. but after read code (at least for audit_add_tree_rule)
during unlock audit_filter_mutex in audit_add_tree_rule:
I find only one posible related work flow which may happen (maybe it can not happen either).
fsnotify_destroy_mark_locked ->
audit_tree_freeing_mark ->
evict_chunk ->
kill_rules ->
call_rcu ->
audit_free_rule_rcu ->
audit_free_rule
it will free rules and entry, but it does not call put_tree().
so I think, at least for audit_add_tree_rule, we can remove the pair of get_tree() and put_tree()
(maybe also need give a check for audit_tag_tree and audit_trim_trees, whether can remove 'get_tree' too)
and the process is incorrect after lock audit_filter_mutex again (line 701..705)
a. if rule->rlist was really empty
the 'rule' itself would already be freed.
the caller and the caller of caller, need notice this (not double free)
instead, we need check tree->gonar (and also need spin_lock protected).
b. we do not need set "rule->tree = tree" again.
i. if 'rule' is not touched by any other thread
it should be rule->tree == tree.
ii. else if rule->tree == NULL (freed by other thread)
'rule' itself might be freed too, we'd better return by failure.
iii. else (!rule->tree && rule->tree != tree) (reused by other thread)
firstly, it should not happen.
if could happen, 'rule->tree = tree' would cause original rule->tree memory leak.
my conclusion is only by reading code (and still I am not quite expert about it, either)
so welcome experts (especially maintainers) to providing suggestions or completions.
thanks.
if no reply within a week (2013-04-28), I should send related patch.
gchen.
653 /* called with audit_filter_mutex */
654 int audit_add_tree_rule(struct audit_krule *rule)
655 {
656 struct audit_tree *seed = rule->tree, *tree;
657 struct path path;
658 struct vfsmount *mnt;
659 int err;
660
661 list_for_each_entry(tree, &tree_list, list) {
662 if (!strcmp(seed->pathname, tree->pathname)) {
663 put_tree(seed);
664 rule->tree = tree;
665 list_add(&rule->rlist, &tree->rules);
666 return 0;
667 }
668 }
669 tree = seed;
670 list_add(&tree->list, &tree_list);
671 list_add(&rule->rlist, &tree->rules);
672 /* do not set rule->tree yet */
673 mutex_unlock(&audit_filter_mutex);
674
675 err = kern_path(tree->pathname, 0, &path);
676 if (err)
677 goto Err;
678 mnt = collect_mounts(&path);
679 path_put(&path);
680 if (IS_ERR(mnt)) {
681 err = PTR_ERR(mnt);
682 goto Err;
683 }
684
685 get_tree(tree);
686 err = iterate_mounts(tag_mount, tree, mnt);
687 drop_collected_mounts(mnt);
688
689 if (!err) {
690 struct node *node;
691 spin_lock(&hash_lock);
692 list_for_each_entry(node, &tree->chunks, list)
693 node->index &= ~(1U<<31);
694 spin_unlock(&hash_lock);
695 } else {
696 trim_marked(tree);
697 goto Err;
698 }
699
700 mutex_lock(&audit_filter_mutex);
701 if (list_empty(&rule->rlist)) {
702 put_tree(tree);
703 return -ENOENT;
704 }
705 rule->tree = tree;
706 put_tree(tree);
707
708 return 0;
709 Err:
710 mutex_lock(&audit_filter_mutex);
711 list_del_init(&tree->list);
712 list_del_init(&tree->rules);
713 put_tree(tree);
714 return err;
715 }
> excuse me:
> I am not quite familiar with it, and also have to do another things.
> so I have to spend additional time resource to make sure about it.
>
> is it ok ?
> I should make sure about it within this week (2013-04-21)
> I should finish related test (if need), within next week (2013-4-28)
>
> if have additional suggestions or completions, please reply.
> (if no reply, I will follow the time point above)
>
> thanks.
>
> gchen.
>
>
--
Chen Gang
Asianux Corporation
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