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

Subsystems: netfilter, networking [general], the rest

STALE3689d

4 messages, 3 authors, 2016-09-07 · open the first message on its own page

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

From: <hidden>
Date: 2016-09-06 14:43:55

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;
+		}
 		nfct_synproxy_ext_add(ct);
 	}

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;
 	}
 
 	if (maniptype == NF_NAT_MANIP_SRC) {

-- 
1.9.1

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

From: Florian Westphal <fw@strlen.de>
Date: 2016-09-06 14:51:21

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

quoted hunk

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;
}

quoted hunk

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?

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

From: Gao Feng <hidden>
Date: 2016-09-06 14:55:15

inline

On Tue, Sep 6, 2016 at 10:51 PM, Florian Westphal [off-list ref] 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;
}

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?

I thought we should drop the packet in that case before.
But Pablo point out one case that the ctnetlink also could add the
seqadj extension too.
There is one synchronization case.

I think he is right. Then modify the patch according to his advice.

Best Regards
Feng

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

From: Pablo Neira Ayuso <pablo@netfilter.org>
Date: 2016-09-07 09:19:11

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!

`h`	back out one level
`j`	next message in thread
`k`	previous message in thread
`l`	drill in
`Esc`	close help / fold thread tree
`?`	toggle this help