Messages in this thread | | | Date | Mon, 23 Jul 2018 11:28:18 +0200 | From | Florian Westphal <> | Subject | Re: [PATCH] netlink: fix memory leak of dump |
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Pablo Neira Ayuso <pablo@netfilter.org> wrote: > > diff --git a/net/netfilter/nf_tables_api.c b/net/netfilter/nf_tables_api.c > > --- a/net/netfilter/nf_tables_api.c > > +++ b/net/netfilter/nf_tables_api.c > > @@ -5010,6 +5013,22 @@ nft_obj_filter_alloc(const struct nlattr * const nla[]) > > return filter; > > } > > > > +static int nf_tables_dump_obj_start(struct netlink_callback *cb) > > +{ > > + const struct nlattr * const *nla = cb->data;
On-Stack input. I can't see how its wrong, ->start() happens from same context as netlink_dump_start so its valid.
> > + struct nft_obj_filter *filter = NULL; > > + > > + if (nla[NFTA_OBJ_TABLE] || > > + nla[NFTA_OBJ_TYPE]) { > > + filter = nft_obj_filter_alloc(nla); > > + if (IS_ERR(filter)) > > + return -ENOMEM; > > + } > > + > > + cb->data = filter;
And this replaced the on-stack input with dynamically allocated one, which will be free'd via ->done().
> > /* called with rcu_read_lock held */ > > static int nf_tables_getobj(struct net *net, struct sock *nlsk, > > struct sk_buff *skb, const struct nlmsghdr *nlh, > > @@ -5028,21 +5047,13 @@ static int nf_tables_getobj(struct net *net, struct sock *nlsk, > > > > if (nlh->nlmsg_flags & NLM_F_DUMP) { > > struct netlink_dump_control c = { > > + .start = nf_tables_dump_obj_start, > > .dump = nf_tables_dump_obj, > > .done = nf_tables_dump_obj_done, > > .module = THIS_MODULE, > > + .data = (void *)nla, > > You cannot do this. > > nla is allocated in this stack.
Yes.
> the nla will not be available in the second recv(), it won't be there.
Its replaced in ->start().
As David pointed out, once ->start() returns 0 we set cb_running, i.e. only after successful ->start() netlink core will call ->dump() again.
So I see no problem setting ->data to onstack cookie and then duplicating it to heap via kmemdup in ->start().
As far as I can see netlink core offers all functionality already, so we only need to switch netfilter to make use of it.
If you disagree please let me know, otherwise I will cook up a patch along this pattern for net/netfilter/*.
Thanks.
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