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

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Date:   Fri, 19 Apr 2019 09:53:22 -0500
From:   Wenwen Wang <wang6495@....edu>
To:     Paul Moore <paul@...l-moore.com>
Cc:     Eric Paris <eparis@...hat.com>,
        "moderated list:AUDIT SUBSYSTEM" <linux-audit@...hat.com>,
        open list <linux-kernel@...r.kernel.org>,
        Wenwen Wang <wang6495@....edu>
Subject: Re: [PATCH] audit: fix a memory leak bug

On Thu, Apr 18, 2019 at 4:52 PM Paul Moore <paul@...l-moore.com> wrote:
>
> 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"?
>
This sounds reasonable to me. I will rework the patch. Thanks!

Wenwen