[PATCH net-next v2 2/8] tls: check for a pending signal after an empty record

[Chuck Lever <cel@kernel.org>]

tls_rx_rec_wait() tests signal_pending() only after it sleeps, and
it skips the wait loop when a record is already parsed.
tls_sw_recvmsg() calls it once per record, and a zero-length
application_data record advances neither of its loop bounds. A
peer that streams such records holds the caller in recvmsg(),
unresponsive to SIGKILL, for as long as they arrive.

Test for a pending signal in tls_sw_recvmsg() before it fetches the
record after an empty one. A reader that has copied data returns
it, and a nonblocking reader gets -EINTR. The test stays out of
tls_rx_rec_wait() because tls_sw_read_sock() also calls it, from
callers that cannot act on a signal.

Fixes: c46234ebb4d1 ("tls: RX path for ktls")
Signed-off-by: Chuck Lever <cel@kernel.org>
---
 net/tls/tls_sw.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/net/tls/tls_sw.c b/net/tls/tls_sw.c
index c78471c53f2f..ee50b9028264 100644
--- a/net/tls/tls_sw.c
+++ b/net/tls/tls_sw.c
@@ -1824,6 +1824,7 @@ int tls_sw_recvmsg(struct sock *sk,
 	bool is_peek = flags & MSG_PEEK;
 	bool rx_more = false;
 	bool released = true;
+	bool nodata = false;
 	bool zc_capable;
 
 	if (unlikely(flags & MSG_ERRQUEUE))
@@ -1858,6 +1859,16 @@ int tls_sw_recvmsg(struct sock *sk,
 		struct tls_decrypt_arg darg;
 		int to_decrypt, chunk;
 
+		/* A run of empty records advances neither loop bound, and
+		 * tls_rx_rec_wait() tests for a signal only after it sleeps.
+		 */
+		if (nodata && signal_pending(current)) {
+			long timeo = sock_rcvtimeo(sk, flags & MSG_DONTWAIT);
+
+			err = sock_intr_errno(timeo);
+			goto recv_end;
+		}
+
 		err = tls_rx_rec_wait(sk, flags & MSG_DONTWAIT,
 				      released, !!(decrypted + copied));
 		if (err <= 0)
@@ -1910,6 +1921,7 @@ int tls_sw_recvmsg(struct sock *sk,
 		/* TLS 1.3 may have updated the length by more than overhead */
 		rxm = strp_msg(darg.skb);
 		chunk = rxm->full_len;
+		nodata = !chunk;
 		tls_rx_rec_done(ctx);
 
 		if (!darg.zc) {

-- 
2.55.0