From: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Date: Tue, 6 Sep 2022 15:59:17 +0000 (-0400)
Subject: Fix: notification capture: handle userspace strings
X-Git-Url: https://git.lttng.org/?p=lttng-modules.git;a=commitdiff_plain;h=8915cf5e47e6dd0ba1baebdb13027b0ce4237c86

Fix: notification capture: handle userspace strings

The "user" attribute (copy from userspace) is not applied to string
field capture within event notifications. This leads to copy of strings
from user-space (e.g. `filename` field from sys_open) to end up using
strlen/memcpy on user-space data. This can cause kernel OOPS due to
unhandled page faults, and it also allows reading kernel memory through
the event notification capture mechanism. As a result, the users within
the `tracing` group can read arbitrary kernel memory.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Change-Id: I3241b144fea849004a3f0a19276506c9f1b0d5e5
---

diff --git a/src/lttng-event-notifier-notification.c b/src/lttng-event-notifier-notification.c
index 811dc50a..054d3339 100644
--- a/src/lttng-event-notifier-notification.c
+++ b/src/lttng-event-notifier-notification.c
@@ -283,7 +283,11 @@ int notification_append_capture(
 		}
 		break;
 	case LTTNG_INTERPRETER_TYPE_STRING:
-		ret = lttng_msgpack_write_str(writer, output->u.str.str);
+		if (output->u.str.user) {
+			ret = lttng_msgpack_write_user_str(writer, output->u.str.user_str);
+		} else {
+			ret = lttng_msgpack_write_str(writer, output->u.str.str);
+		}
 		if (ret) {
 			WARN_ON_ONCE(1);
 			goto end;