net/tls: add TlsDecryptError stat

Add a statistic for TLS record decryption errors.

Since devices are supposed to pass records as-is when they
encounter errors this statistic will count bad records in
both pure software and inline crypto configurations.
Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Documentation/networking/tls.rst

@@ -233,3 +233,6 @@ TLS implementation exposes the following per-namespace statistics
 
 - ``TlsTxDevice``, ``TlsRxDevice`` -
   number of TX and RX sessions opened with NIC cryptography
+
+- ``TlsDecryptError`` -
+  record decryption failed (e.g. due to incorrect authentication tag)

include/uapi/linux/snmp.h

@@ -335,6 +335,7 @@ enum
 	LINUX_MIB_TLSRXSW,			/* TlsRxSw */
 	LINUX_MIB_TLSTXDEVICE,			/* TlsTxDevice */
 	LINUX_MIB_TLSRXDEVICE,			/* TlsRxDevice */
+	LINUX_MIB_TLSDECRYPTERROR,		/* TlsDecryptError */
 	__LINUX_MIB_TLSMAX
 };
 

net/tls/tls_proc.c

@@ -15,6 +15,7 @@ static const struct snmp_mib tls_mib_list[] = {
 	SNMP_MIB_ITEM("TlsRxSw", LINUX_MIB_TLSRXSW),
 	SNMP_MIB_ITEM("TlsTxDevice", LINUX_MIB_TLSTXDEVICE),
 	SNMP_MIB_ITEM("TlsRxDevice", LINUX_MIB_TLSRXDEVICE),
+	SNMP_MIB_ITEM("TlsDecryptError", LINUX_MIB_TLSDECRYPTERROR),
 	SNMP_MIB_SENTINEL
 };
 

net/tls/tls_sw.c

@@ -168,6 +168,9 @@ static void tls_decrypt_done(struct crypto_async_request *req, int err)
 
 	/* Propagate if there was an err */
 	if (err) {
+		if (err == -EBADMSG)
+			TLS_INC_STATS(sock_net(skb->sk),
+				      LINUX_MIB_TLSDECRYPTERROR);
 		ctx->async_wait.err = err;
 		tls_err_abort(skb->sk, err);
 	} else {
@@ -253,6 +256,8 @@ static int tls_do_decryption(struct sock *sk,
 			return ret;
 
 		ret = crypto_wait_req(ret, &ctx->async_wait);
+	} else if (ret == -EBADMSG) {
+		TLS_INC_STATS(sock_net(sk), LINUX_MIB_TLSDECRYPTERROR);
 	}
 
 	if (async)