Re: [bpf PATCH v2 1/6] bpf: sockmap, fix crash when ipv6 sock is added

On 06/14/2018 04:53 PM, Martin KaFai Lau wrote:

On Thu, Jun 14, 2018 at 09:44:46AM -0700, John Fastabend wrote:

quoted

This fixes a crash where we assign tcp_prot to IPv6 sockets instead
of tcpv6_prot.

Previously we overwrote the sk->prot field with tcp_prot even in the
AF_INET6 case. This patch ensures the correct tcp_prot and tcpv6_prot
are used.

quoted

Further, only allow ESTABLISHED connections to join the
map per note in TLS ULP,

   /* The TLS ulp is currently supported only for TCP sockets
    * in ESTABLISHED state.
    * Supporting sockets in LISTEN state will require us
    * to modify the accept implementation to clone rather then
    * share the ulp context.
    */

This bit has been moved to patch 2.

Yep better cut the comment as well.

quoted

Also tested with 'netserver -6' and 'netperf -H [IPv6]' as well as
'netperf -H [IPv4]'. The ESTABLISHED check resolves the previously
crashing case here.

Fixes: 174a79ff9515 ("bpf: sockmap with sk redirect support")
Reported-by: syzbot+5c063698bdbfac19f363@syzkaller.appspotmail.com
Signed-off-by: John Fastabend <john.fastabend@gmail.com>
Signed-off-by: Wei Wang <redacted>
---
 0 files changed

0 files changed will fix that as well.

quoted

diff --git a/kernel/bpf/sockmap.c b/kernel/bpf/sockmap.c
index 52a91d8..f6dd4cd 100644
--- a/kernel/bpf/sockmap.c
+++ b/kernel/bpf/sockmap.c

@@ -140,6 +140,7 @@ static int bpf_tcp_recvmsg(struct sock *sk, struct msghdr *msg, size_t len,
 static int bpf_tcp_sendmsg(struct sock *sk, struct msghdr *msg, size_t size);
 static int bpf_tcp_sendpage(struct sock *sk, struct page *page,
 			    int offset, size_t size, int flags);
+static void bpf_tcp_close(struct sock *sk, long timeout);
 
 static inline struct smap_psock *smap_psock_sk(const struct sock *sk)
 {

@@ -161,7 +162,42 @@ static bool bpf_tcp_stream_read(const struct sock *sk)
 	return !empty;
 }
 
-static struct proto tcp_bpf_proto;
+enum {
+	SOCKMAP_IPV4,
+	SOCKMAP_IPV6,
+	SOCKMAP_NUM_PROTS,
+};
+
+enum {
+	SOCKMAP_BASE,
+	SOCKMAP_TX,
+	SOCKMAP_NUM_CONFIGS,
+};
+
+static struct proto *saved_tcpv6_prot;

__read_mostly

Sure makes sense.

quoted

+static DEFINE_MUTEX(tcpv6_prot_mutex);
+static struct proto bpf_tcp_prots[SOCKMAP_NUM_PROTS][SOCKMAP_NUM_CONFIGS];
+static void build_protos(struct proto prot[SOCKMAP_NUM_CONFIGS],
+			 struct proto *base)
+{
+	prot[SOCKMAP_BASE]			= *base;
+	prot[SOCKMAP_BASE].close		= bpf_tcp_close;
+	prot[SOCKMAP_BASE].recvmsg		= bpf_tcp_recvmsg;
+	prot[SOCKMAP_BASE].stream_memory_read	= bpf_tcp_stream_read;
+
+	prot[SOCKMAP_TX]			= prot[SOCKMAP_BASE];
+	prot[SOCKMAP_TX].sendmsg		= bpf_tcp_sendmsg;
+	prot[SOCKMAP_TX].sendpage		= bpf_tcp_sendpage;
+}
+
+static void update_sk_prot(struct sock *sk, struct smap_psock *psock)
+{
+	int family = sk->sk_family == AF_INET6 ? SOCKMAP_IPV6 : SOCKMAP_IPV4;
+	int conf = psock->bpf_tx_msg ? SOCKMAP_TX : SOCKMAP_BASE;
+
+	sk->sk_prot = &bpf_tcp_prots[family][conf];
+}
+
 static int bpf_tcp_init(struct sock *sk)
 {
 	struct smap_psock *psock;

@@ -181,14 +217,17 @@ static int bpf_tcp_init(struct sock *sk)
 	psock->save_close = sk->sk_prot->close;
 	psock->sk_proto = sk->sk_prot;
 
-	if (psock->bpf_tx_msg) {
-		tcp_bpf_proto.sendmsg = bpf_tcp_sendmsg;
-		tcp_bpf_proto.sendpage = bpf_tcp_sendpage;
-		tcp_bpf_proto.recvmsg = bpf_tcp_recvmsg;
-		tcp_bpf_proto.stream_memory_read = bpf_tcp_stream_read;
+	/* Build IPv6 sockmap whenever the address of tcpv6_prot changes */
+	if (sk->sk_family == AF_INET6 &&
+	    unlikely(sk->sk_prot != smp_load_acquire(&saved_tcpv6_prot))) {
+		mutex_lock(&tcpv6_prot_mutex);

bpf_tcp_init() can be called by skops?
Can mutex_lock() be used here?

No mutex lock can not be used here. Both are called
with rcu_read_lock() and we can not sleep. Thanks
for catching. Also this will give a kernel splat now
that I have the right config options. Guess we need
a v3 :/

Thanks,
John