From: Michael Jeanson <mjeanson@efficios.com>
Date: Thu, 23 Mar 2023 16:45:18 +0000 (-0400)
Subject: Fix: truncated len in lttng_event_rule_user_tracepoint_serialize()
X-Git-Tag: v2.13.10~14
X-Git-Url: https://git.lttng.org/?p=lttng-tools.git;a=commitdiff_plain;h=a989d3e5aea516e321ebd6e021e7c3dedf215a21

Fix: truncated len in lttng_event_rule_user_tracepoint_serialize()

Observed issue
==============

On 64-bit big-endian platforms, the serialization/deserialization tests
of tracepoint event rules fail since the length of individual exclusions
is truncated in lttng_event_rule_user_tracepoint_serialize and appear as
"0" on the receiving end.

Cause
=====

The length of the exclusion name string is stored in a variable of type
`size_t`. However, since the protocol expects it to be expressed as a
uint32_t, the value is added to the payload by copying the first 4 bytes
of the value.

On a 32-bit system this would be fine since `sizeof(size_t) == 4`. Even
worse, it would work most of the time (assuming an exclusion name string
< 4GiB) on a little-endian 64-bit system as the least significant bits
would be copied and correctly express the length of the string.

On a big-endian 64-bit platform, the most-significant 4 bytes are copied
to the payload buffer thus making the string length appear as "0".

Solution
========

A temporary variable is used to hold the "casted" value and make it safe
to copy to the payload buffer regardless of the platform's endianness.

Known drawbacks
===============

None.

Change-Id: I64c03345fff7ffea2f8fcb84692a085da31c421b
Signed-off-by: Michael Jeanson <mjeanson@efficios.com>
Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>
---

diff --git a/src/common/event-rule/user-tracepoint.c b/src/common/event-rule/user-tracepoint.c
index 503e7163f..d5815e7c4 100644
--- a/src/common/event-rule/user-tracepoint.c
+++ b/src/common/event-rule/user-tracepoint.c
@@ -156,6 +156,7 @@ static int lttng_event_rule_user_tracepoint_serialize(
 
 	for (i = 0; i < exclusion_count; i++) {
 		size_t len;
+		uint32_t serialized_len;
 		const char *exclusion;
 
 		status = lttng_event_rule_user_tracepoint_get_name_pattern_exclusion_at_index(
@@ -163,9 +164,11 @@ static int lttng_event_rule_user_tracepoint_serialize(
 		assert(status == LTTNG_EVENT_RULE_STATUS_OK);
 
 		len = strlen(exclusion) + 1;
+
+		serialized_len = len;
 		/* Append exclusion length, includes the null terminator. */
 		ret = lttng_dynamic_buffer_append(
-				&payload->buffer, &len, sizeof(uint32_t));
+				&payload->buffer, &serialized_len, sizeof(serialized_len));
 		if (ret) {
 			goto end;
 		}