[PATCH net] tls: fix send() returning success after the TCP send failed

[Hengyu Liang <hengyul@cs.unc.edu>]

Commit b341ca51d267 ("tls: Fix tls_sw_sendmsg error handling") made
tls_tx_records() pass the error of the TCP send to tls_err_abort()
instead of -EBADMSG.

However, bpf_exec_tx_verdict() still looks for EBADMSG in sk_err to
tell that the record was not sent. With any other error, the record
stays counted. As of now, send() on a kTLS socket returns success after
the TCP connection can no longer send, for example after
shutdown(SHUT_WR) or after a reset. Nothing reaches the peer, and the
caller is not told.

The issue can be reproduced with:

    python3 - <<'EOF'
    import socket, struct
    l = socket.create_server(("127.0.0.1", 0))
    c = socket.create_connection(l.getsockname())
    c.setsockopt(socket.SOL_TCP, 31, b"tls")
    c.setsockopt(282, 1, struct.pack("HH", 0x0303, 51) + bytes(36))
    c.shutdown(socket.SHUT_WR)
    print(c.send(b"hello"))
    EOF

Before commit b341ca51d267 ("tls: Fix tls_sw_sendmsg error handling"),
the result is:

    OSError: [Errno 74] Bad message

After that commit, the result is:

    5

This patch will make bpf_exec_tx_verdict() check for any error in
sk_err. The send() above then fails with EPIPE, as it does on a plain
TCP socket.

Fixes: b341ca51d267 ("tls: Fix tls_sw_sendmsg error handling")
Signed-off-by: Hengyu Liang <hengyul@cs.unc.edu>
---
Tested on net: with this patch, the send() above and a send() after a
reset fail with EPIPE, and a send() on a TCP_REPAIR socket fails with
EINVAL, as they do on a plain TCP socket. The tls selftests pass.

Not addressed here: a caller that ignores the error and sends again
still gets one more record queued per send(), because
sk_stream_error() clears sk_err for EPIPE. Before commit b341ca51d267
the EBADMSG stayed set and later sends failed early.

 net/tls/tls_sw.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/tls/tls_sw.c b/net/tls/tls_sw.c
index 226e0f176fdc..f3e496fa47ae 100644
--- a/net/tls/tls_sw.c
+++ b/net/tls/tls_sw.c
@@ -711,7 +711,7 @@ static int bpf_exec_tx_verdict(struct sk_msg *msg, struct sock *sk,
 	int err;
 
 	err = tls_push_record(sk, flags, record_type);
-	if (err && err != -EINPROGRESS && sk->sk_err == EBADMSG) {
+	if (err && err != -EINPROGRESS && sk->sk_err) {
 		*copied -= sk_msg_free(sk, msg);
 		tls_free_open_rec(sk);
 		err = -sk->sk_err;

base-commit: ead6fa9a0ab194f02a2f36d634b193e9c5f9a1c6
-- 
2.53.0