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 executed
Fixing 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: 8e368dc ("bpf: Fix use of sk->sk_reuseport from sk_assign")
Fixes: cf7fbe6 ("bpf: Add socket assign support")
Co-developed-by: Daniel Borkmann <daniel@xxxxxxxxxxxxx>
Signed-off-by: Daniel Borkmann <daniel@xxxxxxxxxxxxx>
Signed-off-by: Lorenz Bauer <lmb@xxxxxxxxxxxxx>
Cc: Joe Stringer <joe@xxxxxxxxx>
Link: https://lore.kernel.org/bpf/CACAyw98+qycmpQzKupquhkxbvWK4OFyDuuLMBNROnfWMZxUWeA@xxxxxxxxxxxxxx/
---
include/net/inet6_hashtables.h | 36 +++++++++++++++++++++++++++++-----
include/net/inet_hashtables.h | 27 +++++++++++++++++++++++--
include/net/sock.h | 7 +++++--
include/uapi/linux/bpf.h | 3 ---
net/core/filter.c | 2 --
net/ipv4/inet_hashtables.c | 15 +++++++-------
net/ipv4/udp.c | 23 +++++++++++++++++++---
net/ipv6/inet6_hashtables.c | 19 +++++++++---------
net/ipv6/udp.c | 23 +++++++++++++++++++---
tools/include/uapi/linux/bpf.h | 3 ---
10 files changed, 119 insertions(+), 39 deletions(-)
diff --git a/include/net/inet6_hashtables.h b/include/net/inet6_hashtables.h
index 56f1286583d3..3ba4dc2703da 100644
--- a/include/net/inet6_hashtables.h
+++ b/include/net/inet6_hashtables.h
@@ -48,6 +48,13 @@ struct sock *__inet6_lookup_established(struct net *net,
const u16 hnum, const int dif,
const int sdif);
+struct sock *inet6_lookup_reuseport(struct net *net, struct sock *sk,
+ struct sk_buff *skb, int doff,
+ const struct in6_addr *saddr,
+ __be16 sport,
+ const struct in6_addr *daddr,
+ unsigned short hnum);
+
struct sock *inet6_lookup_listener(struct net *net,
struct inet_hashinfo *hashinfo,
struct sk_buff *skb, int doff,
@@ -85,14 +92,33 @@ 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);
-
+ bool prefetched;
+ struct sock *sk = skb_steal_sock(skb, refcounted, &prefetched);
+ struct net *net = dev_net(skb_dst(skb)->dev);
+ const struct ipv6hdr *ip6h = ipv6_hdr(skb);
+
+ if (prefetched) {
+ struct sock *reuse_sk = inet6_lookup_reuseport(net, sk, skb, doff,
+ &ip6h->saddr, sport,
+ &ip6h->daddr, ntohs(dport));
+ if (reuse_sk) {
+ if (reuse_sk != sk) {
+ if (*refcounted) {
+ sock_put(sk);
+ *refcounted = false;
+ }
+ if (IS_ERR(reuse_sk))
+ return NULL;
+ }
+ return reuse_sk;
+ }
+ }
if (sk)
return sk;
- 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 99bd823e97f6..c2af195ca71f 100644
--- a/include/net/inet_hashtables.h
+++ b/include/net/inet_hashtables.h
@@ -379,6 +379,11 @@ struct sock *__inet_lookup_established(struct net *net,
const __be32 daddr, const u16 hnum,
const int dif, const int sdif);
+struct sock *inet_lookup_reuseport(struct net *net, struct sock *sk,
+ struct sk_buff *skb, int doff,
+ __be32 saddr, __be16 sport,
+ __be32 daddr, unsigned short hnum);
+
static inline struct sock *
inet_lookup_established(struct net *net, struct inet_hashinfo *hashinfo,
const __be32 saddr, const __be16 sport,
@@ -436,13 +441,31 @@ static inline struct sock *__inet_lookup_skb(struct inet_hashinfo *hashinfo,
const int sdif,
bool *refcounted)
{
- struct sock *sk = skb_steal_sock(skb, refcounted);
+ bool prefetched;
+ struct sock *sk = skb_steal_sock(skb, refcounted, &prefetched);
+ struct net *net = dev_net(skb_dst(skb)->dev);
const struct iphdr *iph = ip_hdr(skb);
+ if (prefetched) {
+ struct sock *reuse_sk = inet_lookup_reuseport(net, sk, skb, doff,
+ iph->saddr, sport,
+ iph->daddr, ntohs(dport));
+ if (reuse_sk) {
+ if (reuse_sk != sk) {
+ if (*refcounted) {
+ sock_put(sk);
+ *refcounted = false;
+ }
+ if (IS_ERR(reuse_sk))
+ return NULL;
+ }
+ return reuse_sk;
+ }
+ }
if (sk)
return sk;
- 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 656ea89f60ff..5645570c2a64 100644
--- a/include/net/sock.h
+++ b/include/net/sock.h
@@ -2806,20 +2806,23 @@ 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);
skb->destructor = NULL;
skb->sk = NULL;
return sk;
}
+ *prefetched = false;
*refcounted = false;
return NULL;
}
diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 1bb11a6ee667..2af606a525db 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -4144,9 +4144,6 @@ union bpf_attr {
* **-EOPNOTSUPP** if the operation is not supported, for example
* a 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
diff --git a/net/core/filter.c b/net/core/filter.c
index 968139f4a1ac..5f451260849b 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -7265,8 +7265,6 @@ 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;
if (sk_is_refcounted(sk) &&
unlikely(!refcount_inc_not_zero(&sk->sk_refcnt)))
return -ENOENT;
diff --git a/net/ipv4/inet_hashtables.c b/net/ipv4/inet_hashtables.c
index e7391bf310a7..920131e4a65d 100644
--- a/net/ipv4/inet_hashtables.c
+++ b/net/ipv4/inet_hashtables.c
@@ -332,10 +332,10 @@ static inline int compute_score(struct sock *sk, struct net *net,
return score;
}
-static inline struct sock *lookup_reuseport(struct net *net, struct sock *sk,
- struct sk_buff *skb, int doff,
- __be32 saddr, __be16 sport,
- __be32 daddr, unsigned short hnum)
+struct sock *inet_lookup_reuseport(struct net *net, struct sock *sk,
+ struct sk_buff *skb, int doff,
+ __be32 saddr, __be16 sport,
+ __be32 daddr, unsigned short hnum)
{
struct sock *reuse_sk = NULL;
u32 phash;
@@ -346,6 +346,7 @@ static inline struct sock *lookup_reuseport(struct net *net, struct sock *sk,
}
return reuse_sk;
}
+EXPORT_SYMBOL_GPL(inet_lookup_reuseport);
/*
* Here are some nice properties to exploit here. The BSD API
@@ -369,8 +370,8 @@ static struct sock *inet_lhash2_lookup(struct net *net,
sk_nulls_for_each_rcu(sk, node, &ilb2->nulls_head) {
score = compute_score(sk, net, hnum, daddr, dif, sdif);
if (score > hiscore) {
- result = lookup_reuseport(net, sk, skb, doff,
- saddr, sport, daddr, hnum);
+ result = inet_lookup_reuseport(net, sk, skb, doff,
+ saddr, sport, daddr, hnum);
if (result)
return result;
@@ -399,7 +400,7 @@ static inline struct sock *inet_lookup_run_bpf(struct net *net,
if (no_reuseport || IS_ERR_OR_NULL(sk))
return sk;
- reuse_sk = lookup_reuseport(net, sk, skb, doff, saddr, sport, daddr, hnum);
+ reuse_sk = inet_lookup_reuseport(net, sk, skb, doff, saddr, sport, daddr, hnum);
if (reuse_sk)
sk = reuse_sk;
return sk;
diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
index 6893fb867529..c67253386a38 100644
--- a/net/ipv4/udp.c
+++ b/net/ipv4/udp.c
@@ -2426,7 +2426,7 @@ int __udp4_lib_rcv(struct sk_buff *skb, struct udp_table *udptable,
struct rtable *rt = skb_rtable(skb);
__be32 saddr, daddr;
struct net *net = dev_net(skb->dev);
- bool refcounted;
+ bool refcounted, prefetched;
int drop_reason;
drop_reason = SKB_DROP_REASON_NOT_SPECIFIED;
@@ -2455,11 +2455,28 @@ 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 = skb_steal_sock(skb, &refcounted, &prefetched);
if (sk) {
struct dst_entry *dst = skb_dst(skb);
int ret;
+ if (prefetched) {
+ struct sock *reuse_sk = lookup_reuseport(net, sk, skb,
+ saddr, uh->source,
+ daddr, ntohs(uh->dest));
+ if (reuse_sk) {
+ if (reuse_sk != sk) {
+ if (refcounted) {
+ sock_put(sk);
+ refcounted = false;
+ }
+ if (IS_ERR(reuse_sk))
+ goto no_sk;
+ }
+ sk = reuse_sk;
+ }
+ }
+
if (unlikely(rcu_dereference(sk->sk_rx_dst) != dst))
udp_sk_rx_dst_set(sk, dst);
@@ -2476,7 +2493,7 @@ 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/inet6_hashtables.c b/net/ipv6/inet6_hashtables.c
index b64b49012655..b7c56867314e 100644
--- a/net/ipv6/inet6_hashtables.c
+++ b/net/ipv6/inet6_hashtables.c
@@ -111,12 +111,12 @@ static inline int compute_score(struct sock *sk, struct net *net,
return score;
}
-static inline struct sock *lookup_reuseport(struct net *net, struct sock *sk,
- struct sk_buff *skb, int doff,
- const struct in6_addr *saddr,
- __be16 sport,
- const struct in6_addr *daddr,
- unsigned short hnum)
+struct sock *inet6_lookup_reuseport(struct net *net, struct sock *sk,
+ struct sk_buff *skb, int doff,
+ const struct in6_addr *saddr,
+ __be16 sport,
+ const struct in6_addr *daddr,
+ unsigned short hnum)
{
struct sock *reuse_sk = NULL;
u32 phash;
@@ -127,6 +127,7 @@ static inline struct sock *lookup_reuseport(struct net *net, struct sock *sk,
}
return reuse_sk;
}
+EXPORT_SYMBOL_GPL(inet6_lookup_reuseport);
/* called with rcu_read_lock() */
static struct sock *inet6_lhash2_lookup(struct net *net,
@@ -143,8 +144,8 @@ static struct sock *inet6_lhash2_lookup(struct net *net,
sk_nulls_for_each_rcu(sk, node, &ilb2->nulls_head) {
score = compute_score(sk, net, hnum, daddr, dif, sdif);
if (score > hiscore) {
- result = lookup_reuseport(net, sk, skb, doff,
- saddr, sport, daddr, hnum);
+ result = inet6_lookup_reuseport(net, sk, skb, doff,
+ saddr, sport, daddr, hnum);
if (result)
return result;
@@ -175,7 +176,7 @@ static inline struct sock *inet6_lookup_run_bpf(struct net *net,
if (no_reuseport || IS_ERR_OR_NULL(sk))
return sk;
- reuse_sk = lookup_reuseport(net, sk, skb, doff, saddr, sport, daddr, hnum);
+ reuse_sk = inet6_lookup_reuseport(net, sk, skb, doff, saddr, sport, daddr, hnum);
if (reuse_sk)
sk = reuse_sk;
return sk;
diff --git a/net/ipv6/udp.c b/net/ipv6/udp.c
index e5a337e6b970..3fede8ec95c4 100644
--- a/net/ipv6/udp.c
+++ b/net/ipv6/udp.c
@@ -949,7 +949,7 @@ int __udp6_lib_rcv(struct sk_buff *skb, struct udp_table *udptable,
struct net *net = dev_net(skb->dev);
struct udphdr *uh;
struct sock *sk;
- bool refcounted;
+ bool refcounted, prefetched;
u32 ulen = 0;
if (!pskb_may_pull(skb, sizeof(struct udphdr)))
@@ -986,11 +986,28 @@ 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 = skb_steal_sock(skb, &refcounted, &prefetched);
if (sk) {
struct dst_entry *dst = skb_dst(skb);
int ret;
+ if (prefetched) {
+ struct sock *reuse_sk = lookup_reuseport(net, sk, skb,
+ saddr, uh->source,
+ daddr, ntohs(uh->dest));
+ if (reuse_sk) {
+ if (reuse_sk != sk) {
+ if (refcounted) {
+ sock_put(sk);
+ refcounted = false;
+ }
+ if (IS_ERR(reuse_sk))
+ goto no_sk;
+ }
+ sk = reuse_sk;
+ }
+ }
+
if (unlikely(rcu_dereference(sk->sk_rx_dst) != dst))
udp6_sk_rx_dst_set(sk, dst);
@@ -1020,7 +1037,7 @@ 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 1bb11a6ee667..2af606a525db 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -4144,9 +4144,6 @@ union bpf_attr {
* **-EOPNOTSUPP** if the operation is not supported, for example
* a 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
--
2.40.1
