From: Lorenz Bauer lmb@isovalent.com Date: Thu, 20 Jul 2023 17:30:11 +0200
Currently the bpf_sk_assign helper in tc BPF context refuses SO_REUSEPORT sockets. This means we can't use the helper to steer traffic to Envoy, which configures SO_REUSEPORT on its sockets. In turn, we're blocked from removing TPROXY from our setup.
The reason that bpf_sk_assign refuses such sockets is that the bpf_sk_lookup helpers don't execute SK_REUSEPORT programs. Instead, one of the reuseport sockets is selected by hash. This could cause dispatch to the "wrong" socket:
sk = bpf_sk_lookup_tcp(...) // select SO_REUSEPORT by hash bpf_sk_assign(skb, sk) // SK_REUSEPORT wasn't executedFixing this isn't as simple as invoking SK_REUSEPORT from the lookup helpers unfortunately. In the tc context, L2 headers are at the start of the skb, while SK_REUSEPORT expects L3 headers instead.
Instead, we execute the SK_REUSEPORT program when the assigned socket is pulled out of the skb, further up the stack. This creates some trickiness with regards to refcounting as bpf_sk_assign will put both refcounted and RCU freed sockets in skb->sk. reuseport sockets are RCU freed. We can infer that the sk_assigned socket is RCU freed if the reuseport lookup succeeds, but convincing yourself of this fact isn't straight forward. Therefore we defensively check refcounting on the sk_assign sock even though it's probably not required in practice.
Fixes: 8e368dc72e86 ("bpf: Fix use of sk->sk_reuseport from sk_assign") Fixes: cf7fbe660f2d ("bpf: Add socket assign support") Co-developed-by: Daniel Borkmann daniel@iogearbox.net Signed-off-by: Daniel Borkmann daniel@iogearbox.net Cc: Joe Stringer joe@cilium.io Link: https://lore.kernel.org/bpf/CACAyw98+qycmpQzKupquhkxbvWK4OFyDuuLMBNROnfWMZxU... Reviewed-by: Kuniyuki Iwashima kuniyu@amazon.com Signed-off-by: Lorenz Bauer lmb@isovalent.com
include/net/inet6_hashtables.h | 56 ++++++++++++++++++++++++++++++++++++++---- include/net/inet_hashtables.h | 49 ++++++++++++++++++++++++++++++++++-- include/net/sock.h | 7 ++++-- include/uapi/linux/bpf.h | 3 --- net/core/filter.c | 2 -- net/ipv4/udp.c | 8 ++++-- net/ipv6/udp.c | 10 +++++--- tools/include/uapi/linux/bpf.h | 3 --- 8 files changed, 116 insertions(+), 22 deletions(-)
diff --git a/include/net/inet6_hashtables.h b/include/net/inet6_hashtables.h index a6722d6ef80f..284b5ce7205d 100644 --- a/include/net/inet6_hashtables.h +++ b/include/net/inet6_hashtables.h @@ -103,6 +103,46 @@ static inline struct sock *__inet6_lookup(struct net *net, daddr, hnum, dif, sdif); } +static inline +struct sock *inet6_steal_sock(struct net *net, struct sk_buff *skb, int doff,
const struct in6_addr *saddr, const __be16 sport,const struct in6_addr *daddr, const __be16 dport,bool *refcounted, inet6_ehashfn_t *ehashfn)+{
- struct sock *sk, *reuse_sk;
- bool prefetched;
- sk = skb_steal_sock(skb, refcounted, &prefetched);
- if (!sk)
return NULL;- if (!prefetched)
return sk;- if (sk->sk_protocol == IPPROTO_TCP) {
if (sk->sk_state != TCP_LISTEN)return sk;- } else if (sk->sk_protocol == IPPROTO_UDP) {
if (sk->sk_state != TCP_CLOSE)return sk;- } else {
return sk;- }
- reuse_sk = inet6_lookup_reuseport(net, sk, skb, doff,
saddr, sport, daddr, ntohs(dport),ehashfn);- if (!reuse_sk)
return sk;- /* We've chosen a new reuseport sock which is never refcounted. This
* implies that sk also isn't refcounted.*/- WARN_ON_ONCE(*refcounted);
- return reuse_sk;
+}
static inline struct sock *__inet6_lookup_skb(struct inet_hashinfo *hashinfo, struct sk_buff *skb, int doff, const __be16 sport, @@ -110,14 +150,20 @@ static inline struct sock *__inet6_lookup_skb(struct inet_hashinfo *hashinfo, int iif, int sdif, bool *refcounted) {
- struct sock *sk = skb_steal_sock(skb, refcounted);
- struct net *net = dev_net(skb_dst(skb)->dev);
- const struct ipv6hdr *ip6h = ipv6_hdr(skb);
- struct sock *sk;
- sk = inet6_steal_sock(net, skb, doff, &ip6h->saddr, sport, &ip6h->daddr, dport,
refcounted, inet6_ehashfn);- if (IS_ERR(sk))
return NULL;
- return __inet6_lookup(dev_net(skb_dst(skb)->dev), hashinfo, skb,
doff, &ipv6_hdr(skb)->saddr, sport,&ipv6_hdr(skb)->daddr, ntohs(dport),
- return __inet6_lookup(net, hashinfo, skb,
doff, &ip6h->saddr, sport,&ip6h->daddr, ntohs(dport), iif, sdif, refcounted);} diff --git a/include/net/inet_hashtables.h b/include/net/inet_hashtables.h index c0532cc7587f..1177effabed3 100644 --- a/include/net/inet_hashtables.h +++ b/include/net/inet_hashtables.h @@ -449,6 +449,46 @@ static inline struct sock *inet_lookup(struct net *net, return sk; } +static inline +struct sock *inet_steal_sock(struct net *net, struct sk_buff *skb, int doff,
const __be32 saddr, const __be16 sport,const __be32 daddr, const __be16 dport,bool *refcounted, inet_ehashfn_t *ehashfn)+{
- struct sock *sk, *reuse_sk;
- bool prefetched;
- sk = skb_steal_sock(skb, refcounted, &prefetched);
- if (!sk)
return NULL;- if (!prefetched)
return sk;- if (sk->sk_protocol == IPPROTO_TCP) {
if (sk->sk_state != TCP_LISTEN)return sk;- } else if (sk->sk_protocol == IPPROTO_UDP) {
if (sk->sk_state != TCP_CLOSE)return sk;- } else {
return sk;- }
- reuse_sk = inet_lookup_reuseport(net, sk, skb, doff,
saddr, sport, daddr, ntohs(dport),ehashfn);- if (!reuse_sk)
return sk;- /* We've chosen a new reuseport sock which is never refcounted. This
* implies that sk also isn't refcounted.*/- WARN_ON_ONCE(*refcounted);
- return reuse_sk;
+}
static inline struct sock *__inet_lookup_skb(struct inet_hashinfo *hashinfo, struct sk_buff *skb, int doff, @@ -457,13 +497,18 @@ static inline struct sock *__inet_lookup_skb(struct inet_hashinfo *hashinfo, const int sdif, bool *refcounted) {
- struct sock *sk = skb_steal_sock(skb, refcounted);
- struct net *net = dev_net(skb_dst(skb)->dev); const struct iphdr *iph = ip_hdr(skb);
- struct sock *sk;
- sk = inet_steal_sock(net, skb, doff, iph->saddr, sport, iph->daddr, dport,
refcounted, inet_ehashfn);- if (IS_ERR(sk))
return NULL;
- return __inet_lookup(dev_net(skb_dst(skb)->dev), hashinfo, skb,
- return __inet_lookup(net, hashinfo, skb, doff, iph->saddr, sport, iph->daddr, dport, inet_iif(skb), sdif, refcounted);
diff --git a/include/net/sock.h b/include/net/sock.h index 2eb916d1ff64..320f00e69ae9 100644 --- a/include/net/sock.h +++ b/include/net/sock.h @@ -2814,20 +2814,23 @@ sk_is_refcounted(struct sock *sk)
- skb_steal_sock - steal a socket from an sk_buff
- @skb: sk_buff to steal the socket from
- @refcounted: is set to true if the socket is reference-counted
*/
- @prefetched: is set to true if the socket was assigned from bpf
static inline struct sock * -skb_steal_sock(struct sk_buff *skb, bool *refcounted) +skb_steal_sock(struct sk_buff *skb, bool *refcounted, bool *prefetched) { if (skb->sk) { struct sock *sk = skb->sk; *refcounted = true;
if (skb_sk_is_prefetched(skb))
*prefetched = skb_sk_is_prefetched(skb);if (*prefetched) *refcounted = sk_is_refcounted(sk);- *prefetched = false; *refcounted = false; return NULL;
} diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h index 739c15906a65..7fc98f4b63e9 100644 --- a/include/uapi/linux/bpf.h +++ b/include/uapi/linux/bpf.h @@ -4198,9 +4198,6 @@ union bpf_attr {
**-EOPNOTSUPP** if the operation is not supported, for examplea call from outside of TC ingress.
**-ESOCKTNOSUPPORT** if the socket type is not supported
(reuseport).
- long bpf_sk_assign(struct bpf_sk_lookup *ctx, struct bpf_sock *sk, u64 flags)
- Description
Helper is overloaded depending on BPF program type. Thisdiff --git a/net/core/filter.c b/net/core/filter.c index b5b51ef48c5f..7c37f4646c20 100644 --- a/net/core/filter.c +++ b/net/core/filter.c @@ -7351,8 +7351,6 @@ BPF_CALL_3(bpf_sk_assign, struct sk_buff *, skb, struct sock *, sk, u64, flags) return -EOPNOTSUPP; if (unlikely(dev_net(skb->dev) != sock_net(sk))) return -ENETUNREACH;
- if (unlikely(sk_fullsock(sk) && sk->sk_reuseport))
return -ESOCKTNOSUPPORT;diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c index 045eca6ed177..ec1a5f8a2eca 100644 --- a/net/ipv4/udp.c +++ b/net/ipv4/udp.c @@ -2388,7 +2388,11 @@ int __udp4_lib_rcv(struct sk_buff *skb, struct udp_table *udptable, if (udp4_csum_init(skb, uh, proto)) goto csum_error;
- sk = skb_steal_sock(skb, &refcounted);
- sk = inet_steal_sock(net, skb, sizeof(struct udphdr), saddr, uh->source, daddr, uh->dest,
&refcounted, udp_ehashfn);- if (IS_ERR(sk))
goto no_sk;- if (sk) { struct dst_entry *dst = skb_dst(skb); int ret;
@@ -2409,7 +2413,7 @@ int __udp4_lib_rcv(struct sk_buff *skb, struct udp_table *udptable, sk = __udp4_lib_lookup_skb(skb, uh->source, uh->dest, udptable); if (sk) return udp_unicast_rcv_skb(sk, skb, uh);
+no_sk: if (!xfrm4_policy_check(NULL, XFRM_POLICY_IN, skb)) goto drop; nf_reset_ct(skb); diff --git a/net/ipv6/udp.c b/net/ipv6/udp.c index 109f14b17a09..f6fc75edfa23 100644 --- a/net/ipv6/udp.c +++ b/net/ipv6/udp.c @@ -925,9 +925,9 @@ int __udp6_lib_rcv(struct sk_buff *skb, struct udp_table *udptable, enum skb_drop_reason reason = SKB_DROP_REASON_NOT_SPECIFIED; const struct in6_addr *saddr, *daddr; struct net *net = dev_net(skb->dev);
- bool refcounted; struct udphdr *uh; struct sock *sk;
- bool refcounted; u32 ulen = 0;
if (!pskb_may_pull(skb, sizeof(struct udphdr)))
This chunk is unnecessary. If there is no other comments from anyone, it would be good to drop this while merging.
Thanks!
@@ -964,7 +964,11 @@ int __udp6_lib_rcv(struct sk_buff *skb, struct udp_table *udptable, goto csum_error; /* Check if the socket is already available, e.g. due to early demux */
- sk = skb_steal_sock(skb, &refcounted);
- sk = inet6_steal_sock(net, skb, sizeof(struct udphdr), saddr, uh->source, daddr, uh->dest,
&refcounted, udp6_ehashfn);- if (IS_ERR(sk))
goto no_sk;- if (sk) { struct dst_entry *dst = skb_dst(skb); int ret;
@@ -998,7 +1002,7 @@ int __udp6_lib_rcv(struct sk_buff *skb, struct udp_table *udptable, goto report_csum_error; return udp6_unicast_rcv_skb(sk, skb, uh); }
+no_sk: reason = SKB_DROP_REASON_NO_SOCKET; if (!uh->check) diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h index 739c15906a65..7fc98f4b63e9 100644 --- a/tools/include/uapi/linux/bpf.h +++ b/tools/include/uapi/linux/bpf.h @@ -4198,9 +4198,6 @@ union bpf_attr {
**-EOPNOTSUPP** if the operation is not supported, for examplea call from outside of TC ingress.
**-ESOCKTNOSUPPORT** if the socket type is not supported
(reuseport).
- long bpf_sk_assign(struct bpf_sk_lookup *ctx, struct bpf_sock *sk, u64 flags)
- Description
Helper is overloaded depending on BPF program type. This-- 2.41.0