Re: [PATCH v5 nf] netfilter: seqadj: Drop the packet directly when fail to add seqadj extension to avoid dereference NULL pointer later

On Tue, Sep 06, 2016 at 04:51:17PM +0200, Florian Westphal wrote:

fgao@ikuai8.com [off-list ref] wrote:

quoted

From: Gao Feng <redacted>

When memory is exhausted, nfct_seqadj_ext_add may fail to add the seqadj
extension. But the function nf_ct_seqadj_init doesn't check if get valid
seqadj pointer by the nfct_seqadj.

Now drop the packet directly when fail to add seqadj extension to avoid
dereference NULL pointer in nf_ct_seqadj_init.

Signed-off-by: Gao Feng <redacted>
---
 v5: Return NF_ACCEPT instead of NF_DROP when nfct_seqadj_ext_add failed in nf_nat_setup_info
 v4: Drop the packet directly when fail to add seqadj extension;
 v3: Remove the warning log when seqadj is null;
 v2: Remove the unnessary seqadj check in nf_ct_seq_adjust
 v1: Initial patch

 net/netfilter/nf_conntrack_core.c | 6 +++++-
 net/netfilter/nf_nat_core.c       | 3 ++-
 2 files changed, 7 insertions(+), 2 deletions(-)

diff --git a/net/netfilter/nf_conntrack_core.c b/net/netfilter/nf_conntrack_core.c
index dd2c43a..dfa76ce 100644
--- a/net/netfilter/nf_conntrack_core.c
+++ b/net/netfilter/nf_conntrack_core.c

@@ -1036,7 +1036,11 @@ init_conntrack(struct net *net, struct nf_conn *tmpl,
 		return (struct nf_conntrack_tuple_hash *)ct;
 
 	if (tmpl && nfct_synproxy(tmpl)) {
-		nfct_seqadj_ext_add(ct);
+		if (!nfct_seqadj_ext_add(ct)) {
+			nf_conntrack_free(ct);
+			pr_debug("Can't add seqadj extension\n");
+			return NULL;
+		}

if (!nfct_add_synrpxy(ct, tmpl)) {
	nf_conntrack_free(ct);
	return NULL;
}

static bool nf_ct_add_synproxy(struct nf_conn *ct, const struct nf_conn *tmpl)
{
	if (tmpl && nfct_synproxy(tmpl)) {
		if (!nfct_seqadj_ext_add(ct))
			return false;

		if (!nfct_synproxy_ext_add(ct))
			return false;
	}

	return true;
}

I like this helper idea, please send a v6 using this using what
Florian is proposing.

quoted

diff --git a/net/netfilter/nf_nat_core.c b/net/netfilter/nf_nat_core.c
index de31818..f8b916a 100644
--- a/net/netfilter/nf_nat_core.c
+++ b/net/netfilter/nf_nat_core.c

@@ -441,7 +441,8 @@ nf_nat_setup_info(struct nf_conn *ct,
 			ct->status |= IPS_DST_NAT;
 
 		if (nfct_help(ct))
-			nfct_seqadj_ext_add(ct);
+			if (!nfct_seqadj_ext_add(ct))
+				return NF_ACCEPT;
 	}

Hmm, why accept?

We are asked to add extension to rewrite sequence numbers, but
we cannot.  How can the connection work if we cannot munge/track
seqno rewrites?

Actually we could just NF_DROP, but if we add support for ctnetlink to
inject entries with sequence adjustment with no NAT. I think we need
this to get synproxy working with conntrackd state synchronization.

Thanks!