[PATCH 5.18 168/231] netfilter: nf_tables: avoid skb access on nf_stolen

Greg Kroah-Hartman
2022-07-19T13:05:58Z

From: Florian Westphal <fw@strlen.de>

[ Upstream commit e34b9ed96ce3b06c79bf884009b16961ca478f87 ]

When verdict is NF_STOLEN, the skb might have been freed.

When tracing is enabled, this can result in a use-after-free:
1. access to skb->nf_trace
2. access to skb->mark
3. computation of trace id
4. dump of packet payload

To avoid 1, keep a cached copy of skb->nf_trace in the
trace state struct.
Refresh this copy whenever verdict is != STOLEN.

Avoid 2 by skipping skb->mark access if verdict is STOLEN.

3 is avoided by precomputing the trace id.

Only dump the packet when verdict is not "STOLEN".

Reported-by: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
include/net/netfilter/nf_tables.h | 16 ++++++-----
net/netfilter/nf_tables_core.c | 24 ++++++++++++++---
net/netfilter/nf_tables_trace.c | 44 +++++++++++++++++--------------
3 files changed, 55 insertions(+), 29 deletions(-)

diff --git a/include/net/netfilter/nf_tables.h b/include/net/netfilter/nf_tables.h
index f0c3a1ee197c..64cf655c818c 100644
--- a/include/net/netfilter/nf_tables.h
+++ b/include/net/netfilter/nf_tables.h
@@ -1342,24 +1342,28 @@ void nft_unregister_flowtable_type(struct nf_flowtable_type *type);
/**
* struct nft_traceinfo - nft tracing information and state
*
+ * @trace: other struct members are initialised
+ * @nf_trace: copy of skb->nf_trace before rule evaluation
+ * @type: event type (enum nft_trace_types)
+ * @skbid: hash of skb to be used as trace id
+ * @packet_dumped: packet headers sent in a previous traceinfo message
* @pkt: pktinfo currently processed
* @basechain: base chain currently processed
* @chain: chain currently processed
* @rule: rule that was evaluated
* @verdict: verdict given by rule
- * @type: event type (enum nft_trace_types)
- * @packet_dumped: packet headers sent in a previous traceinfo message
- * @trace: other struct members are initialised
*/
struct nft_traceinfo {
+ bool trace;
+ bool nf_trace;
+ bool packet_dumped;
+ enum nft_trace_types type:8;
+ u32 skbid;
const struct nft_pktinfo *pkt;
const struct nft_base_chain *basechain;
const struct nft_chain *chain;
const struct nft_rule_dp *rule;
const struct nft_verdict *verdict;
- enum nft_trace_types type;
- bool packet_dumped;
- bool trace;
};

void nft_trace_init(struct nft_traceinfo *info, const struct nft_pktinfo *pkt,
diff --git a/net/netfilter/nf_tables_core.c b/net/netfilter/nf_tables_core.c
index 53f40e473855..3ddce24ac76d 100644
--- a/net/netfilter/nf_tables_core.c
+++ b/net/netfilter/nf_tables_core.c
@@ -25,9 +25,7 @@ static noinline void __nft_trace_packet(struct nft_traceinfo *info,
const struct nft_chain *chain,
enum nft_trace_types type)
{
- const struct nft_pktinfo *pkt = info->pkt;
-
- if (!info->trace || !pkt->skb->nf_trace)
+ if (!info->trace || !info->nf_trace)
return;

info->chain = chain;
@@ -42,11 +40,24 @@ static inline void nft_trace_packet(struct nft_traceinfo *info,
enum nft_trace_types type)
{
if (static_branch_unlikely(&nft_trace_enabled)) {
+ const struct nft_pktinfo *pkt = info->pkt;
+
+ info->nf_trace = pkt->skb->nf_trace;
info->rule = rule;
__nft_trace_packet(info, chain, type);
}
}

+static inline void nft_trace_copy_nftrace(struct nft_traceinfo *info)
+{
+ if (static_branch_unlikely(&nft_trace_enabled)) {
+ const struct nft_pktinfo *pkt = info->pkt;
+
+ if (info->trace)
+ info->nf_trace = pkt->skb->nf_trace;
+ }
+}
+
static void nft_bitwise_fast_eval(const struct nft_expr *expr,
struct nft_regs *regs)
{
@@ -85,6 +96,7 @@ static noinline void __nft_trace_verdict(struct nft_traceinfo *info,
const struct nft_chain *chain,
const struct nft_regs *regs)
{
+ const struct nft_pktinfo *pkt = info->pkt;
enum nft_trace_types type;

switch (regs->verdict.code) {
@@ -92,8 +104,13 @@ static noinline void __nft_trace_verdict(struct nft_traceinfo *info,
case NFT_RETURN:
type = NFT_TRACETYPE_RETURN;
break;
+ case NF_STOLEN:
+ type = NFT_TRACETYPE_RULE;
+ /* can't access skb->nf_trace; use copy */
+ break;
default:
type = NFT_TRACETYPE_RULE;
+ info->nf_trace = pkt->skb->nf_trace;
break;
}

@@ -254,6 +271,7 @@ nft_do_chain(struct nft_pktinfo *pkt, void *priv)
switch (regs.verdict.code) {
case NFT_BREAK:
regs.verdict.code = NFT_CONTINUE;
+ nft_trace_copy_nftrace(&info);
continue;
case NFT_CONTINUE:
nft_trace_packet(&info, chain, rule,
diff --git a/net/netfilter/nf_tables_trace.c b/net/netfilter/nf_tables_trace.c
index 5041725423c2..1163ba9c1401 100644
--- a/net/netfilter/nf_tables_trace.c
+++ b/net/netfilter/nf_tables_trace.c
@@ -7,7 +7,7 @@
#include <linux/module.h>
#include <linux/static_key.h>
#include <linux/hash.h>
-#include <linux/jhash.h>
+#include <linux/siphash.h>
#include <linux/if_vlan.h>
#include <linux/init.h>
#include <linux/skbuff.h>
@@ -25,22 +25,6 @@
DEFINE_STATIC_KEY_FALSE(nft_trace_enabled);
EXPORT_SYMBOL_GPL(nft_trace_enabled);

-static int trace_fill_id(struct sk_buff *nlskb, struct sk_buff *skb)
-{
- __be32 id;
-
- /* using skb address as ID results in a limited number of
- * values (and quick reuse).
- *
- * So we attempt to use as many skb members that will not
- * change while skb is with netfilter.
- */
- id = (__be32)jhash_2words(hash32_ptr(skb), skb_get_hash(skb),
- skb->skb_iif);
-
- return nla_put_be32(nlskb, NFTA_TRACE_ID, id);
-}
-
static int trace_fill_header(struct sk_buff *nlskb, u16 type,
const struct sk_buff *skb,
int off, unsigned int len)
@@ -186,6 +170,7 @@ void nft_trace_notify(struct nft_traceinfo *info)
struct nlmsghdr *nlh;
struct sk_buff *skb;
unsigned int size;
+ u32 mark = 0;
u16 event;

if (!nfnetlink_has_listeners(nft_net(pkt), NFNLGRP_NFTRACE))
@@ -229,7 +214,7 @@ void nft_trace_notify(struct nft_traceinfo *info)
if (nla_put_be32(skb, NFTA_TRACE_TYPE, htonl(info->type)))
goto nla_put_failure;

- if (trace_fill_id(skb, pkt->skb))
+ if (nla_put_u32(skb, NFTA_TRACE_ID, info->skbid))
goto nla_put_failure;

if (nla_put_string(skb, NFTA_TRACE_CHAIN, info->chain->name))
@@ -249,16 +234,24 @@ void nft_trace_notify(struct nft_traceinfo *info)
case NFT_TRACETYPE_RULE:
if (nft_verdict_dump(skb, NFTA_TRACE_VERDICT, info->verdict))
goto nla_put_failure;
+
+ /* pkt->skb undefined iff NF_STOLEN, disable dump */
+ if (info->verdict->code == NF_STOLEN)
+ info->packet_dumped = true;
+ else
+ mark = pkt->skb->mark;
+
break;
case NFT_TRACETYPE_POLICY:
+ mark = pkt->skb->mark;
+
if (nla_put_be32(skb, NFTA_TRACE_POLICY,
htonl(info->basechain->policy)))
goto nla_put_failure;
break;
}

- if (pkt->skb->mark &&
- nla_put_be32(skb, NFTA_TRACE_MARK, htonl(pkt->skb->mark)))
+ if (mark && nla_put_be32(skb, NFTA_TRACE_MARK, htonl(mark)))
goto nla_put_failure;

if (!info->packet_dumped) {
@@ -283,9 +276,20 @@ void nft_trace_init(struct nft_traceinfo *info, const struct nft_pktinfo *pkt,
const struct nft_verdict *verdict,
const struct nft_chain *chain)
{
+ static siphash_key_t trace_key __read_mostly;
+ struct sk_buff *skb = pkt->skb;
+
info->basechain = nft_base_chain(chain);
info->trace = true;
+ info->nf_trace = pkt->skb->nf_trace;
info->packet_dumped = false;
info->pkt = pkt;
info->verdict = verdict;
+
+ net_get_random_once(&trace_key, sizeof(trace_key));
+
+ info->skbid = (u32)siphash_3u32(hash32_ptr(skb),
+ skb_get_hash(skb),
+ skb->skb_iif,
+ &trace_key);
}
--
2.35.1