[PATCH net] tls: improve lockless access safety of tls_err_abort()

[Jakub Kicinski <kuba@kernel.org>]

Most protos' poll() methods insert a memory barrier between
writes to sk_err and sk_error_report(). This dates back to
commit a4d258036ed9 ("tcp: Fix race in tcp_poll").

I guess we should do the same thing in TLS, tcp_poll() does
not hold the socket lock.

Fixes: 3c4d7559159b ("tls: kernel TLS support")
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
---
 net/tls/tls_strp.c | 4 +++-
 net/tls/tls_sw.c   | 4 +++-
 2 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/net/tls/tls_strp.c b/net/tls/tls_strp.c
index 955ac3e0bf4d..1f7696b060d5 100644
--- a/net/tls/tls_strp.c
+++ b/net/tls/tls_strp.c
@@ -20,7 +20,9 @@ static void tls_strp_abort_strp(struct tls_strparser *strp, int err)
 	strp->stopped = 1;
 
 	/* Report an error on the lower socket */
-	strp->sk->sk_err = -err;
+	WRITE_ONCE(strp->sk->sk_err, -err);
+	/* Paired with smp_rmb() in tcp_poll() */
+	smp_wmb();
 	sk_error_report(strp->sk);
 }
 
diff --git a/net/tls/tls_sw.c b/net/tls/tls_sw.c
index 635b8bf6b937..eaf08777abdc 100644
--- a/net/tls/tls_sw.c
+++ b/net/tls/tls_sw.c
@@ -70,7 +70,9 @@ noinline void tls_err_abort(struct sock *sk, int err)
 {
 	WARN_ON_ONCE(err >= 0);
 	/* sk->sk_err should contain a positive error code. */
-	sk->sk_err = -err;
+	WRITE_ONCE(sk->sk_err, -err);
+	/* Paired with smp_rmb() in tcp_poll() */
+	smp_wmb();
 	sk_error_report(sk);
 }
 
-- 
2.40.1