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 279ae0fff7ad..5c4e5a96a984 100644 --- a/include/net/netfilter/nf_tables.h +++ b/include/net/netfilter/nf_tables.h @@ -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, 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); }