[PATCH 5.1 077/122] tracing: probeevent: Fix to make the type of $comm string

[Greg Kroah-Hartman]

From: Masami Hiramatsu <mhiramat@xxxxxxxxxx>

commit 3dd1f7f24f8ceec00bbbc364c2ac3c893f0fdc4c upstream.

Fix to make the type of $comm "string".  If we set the other type to $comm
argument, it shows meaningless value or wrong data. Currently probe events
allow us to set string array type (e.g. ":string[2]"), or other digit types
like x8 on $comm. But since clearly $comm is just a string data, it should
not be fetched by other types including array.

Link: http://lkml.kernel.org/r/155723736241.9149.14582064184468574539.stgit@devnote2

Cc: Andreas Ziegler <andreas.ziegler@xxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Fixes: 533059281ee5 ("tracing: probeevent: Introduce new argument fetching code")
Signed-off-by: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
Signed-off-by: Steven Rostedt (VMware) <rostedt@xxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 kernel/trace/trace_probe.c |   13 +++++++------
 1 file changed, 7 insertions(+), 6 deletions(-)

--- a/kernel/trace/trace_probe.c
+++ b/kernel/trace/trace_probe.c
@@ -420,13 +420,14 @@ static int traceprobe_parse_probe_arg_bo
 				return -E2BIG;
 		}
 	}
-	/*
-	 * The default type of $comm should be "string", and it can't be
-	 * dereferenced.
-	 */
-	if (!t && strcmp(arg, "$comm") == 0)
+
+	/* Since $comm can not be dereferred, we can find $comm by strcmp */
+	if (strcmp(arg, "$comm") == 0) {
+		/* The type of $comm must be "string", and not an array. */
+		if (parg->count || (t && strcmp(t, "string")))
+			return -EINVAL;
 		parg->type = find_fetch_type("string");
-	else
+	} else
 		parg->type = find_fetch_type(t);
 	if (!parg->type) {
 		pr_info("Unsupported type: %s\n", t);