Re: [PATCH v2] kernel: audit_tree: resource management: need put_tree and goto Err when failure occures

[Chen Gang <gang.chen@asianux.com>]

On 2013年04月20日 15:31, Chen Gang wrote:
> 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@asianux.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:
>>>> >> > 
> 

I hope the maintainers to provide your suggestions or completion. if we
get non-reply from any maintainers, I should continue to analyse.

if we continue analyse independent with original maintainers,
I think, before get a conclusion:

  I should understand the API of audit: what it is, how to use it (test
it), know about all of sub-systems which are related with it (such as fs
sub-system);

  also should know about the design of audit (read through the code),

  and should analyse the lower-level design of audit tree (read the code
completely).

and excuse me, I am not quite familiar with audit, now, and also have to
plan to do another things, so I think I should get a conclusion within
next month (2013-05-31), is it ok ?


BTW:
  my plan for 1st half of 2013 is mainly for familiar environments: can
provide contributes to many various sub systems (e.g. arm, powerpc,
drivers, net, kernel ...)

  my plan for 2nd half of 2013 is mainly for familiar kernel: should
analyse the deeper issues and kernel API/design step by step (e.g. mm,
fs, kernel API documents...)

  the original related mail:
http://linux-kernel.2935.n7.nabble.com/Consult-Plan-personal-contributes-plan-for-2013-td587319.html


> 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
> 


-- 
Chen Gang

Asianux Corporation