[PATCH] tls: rx: restore msg_iter before TLS 1.3 optimistic retry

tls_decrypt_sg() advances msg->msg_iter when it maps user pages for
the optimistic TLS 1.3 zero-copy path. If the decrypted record turns
out not to be unpadded application data, tls_decrypt_sw() retries into
a kernel skb, but leaves the iterator advanced.

The subsequent copy from the skb then writes decrypted bytes again at
a later point in the caller iovecs while recvmsg() reports only the
post-retry length. A TLS peer can trigger this after the receiver
enables TLS_RX_EXPECT_NO_PAD.

Revert the iterator by the number of bytes consumed by the optimistic
mapping before retrying without zero-copy.

Add a selftest which sends a TLS 1.3 control record with
TLS_RX_EXPECT_NO_PAD enabled and verifies that recvmsg() does not
overwrite later iovecs beyond the returned length.

Fixes: ce61327ce989 ("tls: rx: support optimistic decrypt to user buffer with TLS 1.3")
Cc: [email protected]
Assisted-by: Codex:gpt-5
Signed-off-by: Jérémy Jean <[email protected]>
---
 net/tls/tls_sw.c                  |  2 ++
 tools/testing/selftests/net/tls.c | 57 +++++++++++++++++++++++++++++++
 2 files changed, 59 insertions(+)

diff --git a/net/tls/tls_sw.c b/net/tls/tls_sw.c
index d4afc90fd796..fcf95978be38 100644
--- a/net/tls/tls_sw.c
+++ b/net/tls/tls_sw.c
@@ -1442,6 +1442,8 @@ tls_decrypt_sw(struct sock *sk, struct tls_context *tls_ctx,
 	/* If opportunistic TLS 1.3 ZC failed retry without ZC */
 	if (unlikely(darg->zc && prot->version == TLS_1_3_VERSION &&
 		     darg->tail != TLS_RECORD_TYPE_DATA)) {
+		iov_iter_revert(&msg->msg_iter, strp_msg(darg->skb)->full_len -
+				prot->overhead_size);
 		darg->zc = false;
 		if (!darg->tail)
 			TLS_INC_STATS(sock_net(sk), LINUX_MIB_TLSRXNOPADVIOL);
diff --git a/tools/testing/selftests/net/tls.c b/tools/testing/selftests/net/tls.c
index cbdd3ea28b99..af5e3314c017 100644
--- a/tools/testing/selftests/net/tls.c
+++ b/tools/testing/selftests/net/tls.c
@@ -1802,6 +1802,63 @@ TEST_F(tls, recv_efault)
 }
 
 #define TLS_RECORD_TYPE_HANDSHAKE      0x16
+
+TEST_F(tls_basic, recvmsg_nopad_retry_iov)
+{
+	char payload[32];
+	char first_iov[sizeof(payload)];
+	char later_iov[sizeof(payload) * 2];
+	char expected_later_iov[sizeof(later_iov)];
+	char cbuf[CMSG_SPACE(sizeof(char))];
+	struct tls_crypto_info_keys tls13;
+	struct iovec iov[] = {
+		{ .iov_base = first_iov, .iov_len = sizeof(first_iov) },
+		{ .iov_base = later_iov, .iov_len = sizeof(later_iov) },
+	};
+	struct msghdr msg = {
+		.msg_iov = iov,
+		.msg_iovlen = ARRAY_SIZE(iov),
+		.msg_control = cbuf,
+		.msg_controllen = sizeof(cbuf),
+	};
+	int one = 1;
+	int ret;
+	int i;
+
+	if (self->notls)
+		SKIP(return, "no TLS support");
+
+	tls_crypto_info_init(TLS_1_3_VERSION, TLS_CIPHER_AES_GCM_128,
+			     &tls13, 0);
+
+	ret = setsockopt(self->fd, SOL_TLS, TLS_TX, &tls13, tls13.len);
+	ASSERT_EQ(ret, 0);
+
+	ret = setsockopt(self->cfd, SOL_TLS, TLS_RX, &tls13, tls13.len);
+	ASSERT_EQ(ret, 0);
+
+	ret = setsockopt(self->cfd, SOL_TLS, TLS_RX_EXPECT_NO_PAD,
+			 &one, sizeof(one));
+	ASSERT_EQ(ret, 0);
+
+	for (i = 0; i < sizeof(payload); i++)
+		payload[i] = 0x40 + i;
+	memset(first_iov, 0xa5, sizeof(first_iov));
+	memset(later_iov, 0x5a, sizeof(later_iov));
+	memset(expected_later_iov, 0x5a, sizeof(expected_later_iov));
+
+	/* A control record forces optimistic TLS 1.3 RX to retry. */
+	ret = tls_send_cmsg(self->fd, TLS_RECORD_TYPE_HANDSHAKE,
+			    payload, sizeof(payload), 0);
+	ASSERT_EQ(ret, sizeof(payload));
+
+	ret = recvmsg(self->cfd, &msg, 0);
+	ASSERT_EQ(ret, sizeof(payload));
+	EXPECT_EQ(memcmp(first_iov, payload, sizeof(payload)), 0);
+	EXPECT_EQ(memcmp(later_iov, expected_later_iov,
+			 sizeof(later_iov)), 0);
+}
+
 /* key_update, length 1, update_not_requested */
 static const char key_update_msg[] = "\x18\x00\x00\x01\x00";
 static void tls_send_keyupdate(struct __test_metadata *_metadata, int fd)
-- 
2.47.3