Merge branch 'fix-sockmap'

John Fastabend says:

====================
Fix a splat introduced by recent changes to avoid skipping ingress policy
when kTLS is enabled. The RCU splat was introduced because in the non-TLS
case the caller is wrapped in an rcu_read_lock/unlock. But, in the TLS
case we have a reference to the psock and the caller did not wrap its
call in rcu_read_lock/unlock.

To fix extend the RCU section to include the redirect case which was
missed. From v1->v2 I changed the location a bit to simplify the code
some. See patch 1.

But, then Martin asked why it was not needed in the non-TLS case. The
answer for patch 1 was, as stated above, because the caller has the
rcu read lock. However, there was still a missing case where a BPF
user could in-theory line up a set of parameters to hit a case
where the code was entered from strparser side from a different context
then the initial caller. To hit this user would need a parser program
to return value greater than skb->len then an ENOMEM error could happen
in the strparser codepath triggering strparser to retry from a workqueue
and without rcu_read_lock original caller used. See patch 2 for details.

Finally, we don't actually have any selftests for parser returning a
value geater than skb->len so add one in patch 3. This is especially
needed because at least I don't have any code that uses the parser
to return value greater than skb->len. So I wouldn't have caught any
errors here in my own testing.

Thanks, John

v1->v2: simplify code in patch 1 some and add patches 2 and 3.
====================

Signed-off-by: Alexei Starovoitov <ast@kernel.org>

1 files changed, 15 insertions, 8 deletions

diff --git a/net/core/skmsg.c b/net/core/skmsg.c
index 351afbf6bfba..6a32a1fd34f8 100644
--- a/net/core/skmsg.c
+++ b/net/core/skmsg.c
@@ -683,7 +683,7 @@ static struct sk_psock *sk_psock_from_strp(struct strparser *strp)
 	return container_of(parser, struct sk_psock, parser);
 }
 
-static void sk_psock_skb_redirect(struct sk_psock *psock, struct sk_buff *skb)
+static void sk_psock_skb_redirect(struct sk_buff *skb)
 {
 	struct sk_psock *psock_other;
 	struct sock *sk_other;
@@ -715,12 +715,11 @@ static void sk_psock_skb_redirect(struct sk_psock *psock, struct sk_buff *skb)
 	}
 }
 
-static void sk_psock_tls_verdict_apply(struct sk_psock *psock,
-				       struct sk_buff *skb, int verdict)
+static void sk_psock_tls_verdict_apply(struct sk_buff *skb, int verdict)
 {
 	switch (verdict) {
 	case __SK_REDIRECT:
-		sk_psock_skb_redirect(psock, skb);
+		sk_psock_skb_redirect(skb);
 		break;
 	case __SK_PASS:
 	case __SK_DROP:
@@ -741,8 +740,8 @@ int sk_psock_tls_strp_read(struct sk_psock *psock, struct sk_buff *skb)
 		ret = sk_psock_bpf_run(psock, prog, skb);
 		ret = sk_psock_map_verd(ret, tcp_skb_bpf_redirect_fetch(skb));
 	}
+	sk_psock_tls_verdict_apply(skb, ret);
 	rcu_read_unlock();
-	sk_psock_tls_verdict_apply(psock, skb, ret);
 	return ret;
 }
 EXPORT_SYMBOL_GPL(sk_psock_tls_strp_read);
@@ -770,7 +769,7 @@ static void sk_psock_verdict_apply(struct sk_psock *psock,
 		}
 		goto out_free;
 	case __SK_REDIRECT:
-		sk_psock_skb_redirect(psock, skb);
+		sk_psock_skb_redirect(skb);
 		break;
 	case __SK_DROP:
 		/* fall-through */
@@ -782,11 +781,18 @@ out_free:
 
 static void sk_psock_strp_read(struct strparser *strp, struct sk_buff *skb)
 {
-	struct sk_psock *psock = sk_psock_from_strp(strp);
+	struct sk_psock *psock;
 	struct bpf_prog *prog;
 	int ret = __SK_DROP;
+	struct sock *sk;
 
 	rcu_read_lock();
+	sk = strp->sk;
+	psock = sk_psock(sk);
+	if (unlikely(!psock)) {
+		kfree_skb(skb);
+		goto out;
+	}
 	prog = READ_ONCE(psock->progs.skb_verdict);
 	if (likely(prog)) {
 		skb_orphan(skb);
@@ -794,8 +800,9 @@ static void sk_psock_strp_read(struct strparser *strp, struct sk_buff *skb)
 		ret = sk_psock_bpf_run(psock, prog, skb);
 		ret = sk_psock_map_verd(ret, tcp_skb_bpf_redirect_fetch(skb));
 	}
-	rcu_read_unlock();
 	sk_psock_verdict_apply(psock, skb, ret);
+out:
+	rcu_read_unlock();
 }
 
 static int sk_psock_strp_read_done(struct strparser *strp, int err)