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netfilter: nf_tables: avoid skb access on nf_stolen

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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>
This commit is contained in:
Florian Westphal 2022-06-22 16:43:57 +02:00 committed by Pablo Neira Ayuso
parent 05907f10e2
commit e34b9ed96c
3 changed files with 55 additions and 29 deletions
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16
include/net/netfilter/nf_tables.h
View file

@ -1338,24 +1338,28 @@ 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,

24
net/netfilter/nf_tables_core.c
View file

@ -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,

44
net/netfilter/nf_tables_trace.c
View file

@ -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);
}