[DTrace-devel] [PATCH 04/05] dynvar: report error if dynvarsize is too small

[Kris Van Hees]

When dynamic variables (or associative arrays) are used, ensure that the
dynvarsize value is sufficient to hold at least one dynamic variable
(or associative array element).

Signed-off-by: Kris Van Hees <kris.van.hees at oracle.com>
---
 libdtrace/dt_bpf.c                            |  5 ++--
 .../assocs/err.dynvarsize-too-small.d         | 30 +++++++++++++++++++
 .../assocs/err.dynvarsize-too-small.r         |  3 ++
 3 files changed, 36 insertions(+), 2 deletions(-)
 create mode 100644 test/unittest/assocs/err.dynvarsize-too-small.d
 create mode 100644 test/unittest/assocs/err.dynvarsize-too-small.r

diff --git a/libdtrace/dt_bpf.c b/libdtrace/dt_bpf.c
index b553b33f..a00b353d 100644
--- a/libdtrace/dt_bpf.c
+++ b/libdtrace/dt_bpf.c
@@ -843,9 +843,10 @@ gmap_create_dvars(dtrace_hdl_t *dtp)
 	if (dtp->dt_maxdvarsize == 0)
 		return 0;
 
-	nelems = dtp->dt_options[DTRACEOPT_DYNVARSIZE] / dtp->dt_maxdvarsize;
+	nelems = dtp->dt_options[DTRACEOPT_DYNVARSIZE] /
+		 (dtp->dt_maxtuplesize + dtp->dt_maxdvarsize);
 	if (nelems == 0)
-		return 0;
+		return dt_set_errno(dtp, EDT_BUFTOOSMALL);
 
 	if (create_gmap(dtp, "dvars", BPF_MAP_TYPE_HASH, sizeof(uint64_t),
 			dtp->dt_maxdvarsize, nelems) == -1)
diff --git a/test/unittest/assocs/err.dynvarsize-too-small.d b/test/unittest/assocs/err.dynvarsize-too-small.d
new file mode 100644
index 00000000..02fa4f8a
--- /dev/null
+++ b/test/unittest/assocs/err.dynvarsize-too-small.d
@@ -0,0 +1,30 @@
+/*
+ * Oracle Linux DTrace.
+ * Copyright (c) 2023, Oracle and/or its affiliates. All rights reserved.
+ * Licensed under the Universal Permissive License v 1.0 as shown at
+ * http://oss.oracle.com/licenses/upl.
+ */
+
+/*
+ * ASSERTION: If dynvarsize is too small to hold a single dynamic variable,
+ *	      report an error.
+ *
+ * SECTION: Aggregations/Aggregations
+ */
+
+/*
+ * Storing an int (4 byte integer) in an associative array indexed by an int
+ * requires at least 20 bytes of dynamic variable storage.
+ */
+#pragma D option dynvarsize=15
+
+BEGIN
+{
+	a[1] = 1;
+	exit(0);
+}
+
+ERROR
+{
+	exit(1);
+}
diff --git a/test/unittest/assocs/err.dynvarsize-too-small.r b/test/unittest/assocs/err.dynvarsize-too-small.r
new file mode 100644
index 00000000..4b56154d
--- /dev/null
+++ b/test/unittest/assocs/err.dynvarsize-too-small.r
@@ -0,0 +1,3 @@
+-- @@stderr --
+dtrace: script 'test/unittest/assocs/err.dynvarsize-too-small.d' matched 2 probes
+dtrace: could not enable tracing: Enabling exceeds size of buffer
-- 
2.40.1