From mboxrd@z Thu Jan 1 00:00:00 1970 From: Kees Cook Subject: [PATCH v2] netfilter: nfnetlink: Remove VLA usage Date: Wed, 30 May 2018 12:17:56 -0700 Message-ID: <20180530191756.GA39504@beast> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Jozsef Kadlecsik , Florian Westphal , "David S. Miller" , netfilter-devel@vger.kernel.org, coreteam@netfilter.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org To: Pablo Neira Ayuso Return-path: Content-Disposition: inline Sender: linux-kernel-owner@vger.kernel.org List-Id: netfilter-devel.vger.kernel.org In the quest to remove all stack VLA usage from the kernel[1], this allocates the maximum size expected for all possible attrs and adds sanity-checks at both registration and usage to make sure nothing gets out of sync. [1] https://lkml.kernel.org/r/CA+55aFzCG-zNmZwX4A2FQpadafLfEzK6CC=qPXydAacU1RqZWA@mail.gmail.com Signed-off-by: Kees Cook --- v2: Use a static value and add a check in nfnetlink_subsys_register() --- net/netfilter/nfnetlink.c | 25 +++++++++++++++++++++++-- 1 file changed, 23 insertions(+), 2 deletions(-) diff --git a/net/netfilter/nfnetlink.c b/net/netfilter/nfnetlink.c index 03ead8a9e90c..1a80fdcf008f 100644 --- a/net/netfilter/nfnetlink.c +++ b/net/netfilter/nfnetlink.c @@ -37,6 +37,8 @@ MODULE_ALIAS_NET_PF_PROTO(PF_NETLINK, NETLINK_NETFILTER); rcu_dereference_protected(table[(id)].subsys, \ lockdep_nfnl_is_held((id))) +#define NFNL_MAX_ATTR_COUNT 32 + static struct { struct mutex mutex; const struct nfnetlink_subsystem __rcu *subsys; @@ -76,6 +78,13 @@ EXPORT_SYMBOL_GPL(lockdep_nfnl_is_held); int nfnetlink_subsys_register(const struct nfnetlink_subsystem *n) { + u8 cb_id; + + /* Sanity-check attr_count size to avoid stack buffer overflow. */ + for (cb_id = 0; cb_id < n->cb_count; cb_id++) + if (WARN_ON(n->cb[cb_id].attr_count > NFNL_MAX_ATTR_COUNT)) + return -EINVAL; + nfnl_lock(n->subsys_id); if (table[n->subsys_id].subsys) { nfnl_unlock(n->subsys_id); @@ -185,11 +194,17 @@ static int nfnetlink_rcv_msg(struct sk_buff *skb, struct nlmsghdr *nlh, { int min_len = nlmsg_total_size(sizeof(struct nfgenmsg)); u8 cb_id = NFNL_MSG_TYPE(nlh->nlmsg_type); - struct nlattr *cda[ss->cb[cb_id].attr_count + 1]; + struct nlattr *cda[NFNL_MAX_ATTR_COUNT + 1]; struct nlattr *attr = (void *)nlh + min_len; int attrlen = nlh->nlmsg_len - min_len; __u8 subsys_id = NFNL_SUBSYS_ID(type); + /* Sanity-check NFNL_MAX_ATTR_COUNT */ + if (ss->cb[cb_id].attr_count > NFNL_MAX_ATTR_COUNT) { + rcu_read_unlock(); + return -ENOMEM; + } + err = nla_parse(cda, ss->cb[cb_id].attr_count, attr, attrlen, ss->cb[cb_id].policy, extack); if (err < 0) { @@ -379,10 +394,16 @@ static void nfnetlink_rcv_batch(struct sk_buff *skb, struct nlmsghdr *nlh, { int min_len = nlmsg_total_size(sizeof(struct nfgenmsg)); u8 cb_id = NFNL_MSG_TYPE(nlh->nlmsg_type); - struct nlattr *cda[ss->cb[cb_id].attr_count + 1]; + struct nlattr *cda[NFNL_MAX_ATTR_COUNT + 1]; struct nlattr *attr = (void *)nlh + min_len; int attrlen = nlh->nlmsg_len - min_len; + /* Sanity-check NFTA_MAX_ATTR */ + if (ss->cb[cb_id].attr_count > NFNL_MAX_ATTR_COUNT) { + err = -ENOMEM; + goto ack; + } + err = nla_parse(cda, ss->cb[cb_id].attr_count, attr, attrlen, ss->cb[cb_id].policy, NULL); if (err < 0) -- 2.17.0 -- Kees Cook Pixel Security