Fix strlen_user fault space reservation

The previous fix took care of kernel OOPS, but did not reserve space for
the \0.

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

diff --git a/probes/lttng-events.h b/probes/lttng-events.h
index 54a451e53388eda82d279d3ec1a98e6a398314f0..ff6273fb3541ced6d2e46d2b7261a2e609b9d257 100644 (file)
--- a/probes/lttng-events.h
+++ b/probes/lttng-events.h
@@ -341,11 +341,13 @@ static __used struct lttng_probe_desc TP_ID(__probe_desc___, TRACE_SYSTEM) = {
        __event_len += __dynamic_len[__dynamic_len_idx++] = strlen(_src) + 1;
 
 /*
- * strlen_user includes \0. If returns 0, it faulted.
+ * strlen_user includes \0. If returns 0, it faulted, so we set size to
+ * 1 (\0 only).
  */
 #undef __string_from_user
 #define __string_from_user(_item, _src)                                               \
-       __event_len += __dynamic_len[__dynamic_len_idx++] = strlen_user(_src);
+       __event_len += __dynamic_len[__dynamic_len_idx++] =                    \
+               min_t(size_t, strlen_user(_src), 1);
 
 #undef TP_PROTO
 #define TP_PROTO(args...) args
@@ -543,9 +545,7 @@ __assign_##dest##_2:                                                        \
        goto __end_field_##dest;
 
 /*
- * If string length is zero, this means reading the string faulted, so
- * we simply put a \0. If string length is larger than 0, it is the
- * string length including the final \0.
+ * The string length including the final \0.
  */
 #undef tp_copy_string_from_user
 #define tp_copy_string_from_user(dest, src)                            \