linux-kernel - Re: [PATCH] audit: fix a memory leak bug

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Date:   Thu, 18 Apr 2019 17:52:06 -0400
From:   Paul Moore <paul@...l-moore.com>
To:     Wenwen Wang <wang6495@....edu>
Cc:     Eric Paris <eparis@...hat.com>,
        "moderated list:AUDIT SUBSYSTEM" <linux-audit@...hat.com>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] audit: fix a memory leak bug

On Thu, Apr 18, 2019 at 1:39 PM Wenwen Wang <wang6495@....edu> wrote:
> In audit_rule_change(), audit_data_to_entry() is firstly invoked to
> translate the payload data to the kernel's rule representation. In
> audit_data_to_entry(), depending on the audit field type, an audit tree may
> be created in audit_make_tree(), which eventually invokes kmalloc() to
> allocate the tree.  Since this tree is a temporary tree, it will be then
> freed in the following execution, e.g., audit_add_rule() if the message
> type is AUDIT_ADD_RULE or audit_del_rule() if the message type is
> AUDIT_DEL_RULE. However, if the message type is neither AUDIT_ADD_RULE nor
> AUDIT_DEL_RULE, i.e., the default case of the switch statement, this
> temporary tree is not freed.
>
> To fix this issue, free the allocated tree in the default case.
>
> Signed-off-by: Wenwen Wang <wang6495@....edu>
> ---
>  kernel/auditfilter.c | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/kernel/auditfilter.c b/kernel/auditfilter.c
> index 63f8b3f..70a34db 100644
> --- a/kernel/auditfilter.c
> +++ b/kernel/auditfilter.c
> @@ -1128,6 +1128,8 @@ int audit_rule_change(int type, int seq, void *data, size_t datasz)
>                 audit_log_rule_change("remove_rule", &entry->rule, !err);
>                 break;
>         default:
> +               if (entry->rule.tree)
> +                       audit_put_tree(entry->rule.tree);
>                 err = -EINVAL;
>                 WARN_ON(1);
>         }

Since there are only two "types" (_ADD_RULE and _DEL_RULE) and the
allocation is only three lines (audit_data_to_entry() + two lines for
error handling), maybe it makes more sense to duplicate the
audit_data_to_entry() call into the individual case statements so we
are only doing the allocations when we have a valid "type"?

-- 
paul moore
www.paul-moore.com