linux-kernel - [PATCH v2 3/3] tracing: probeevent: Fix to make the type of $comm string

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Message-Id: <154778672210.19927.871647535916796323.stgit@devbox>
Date:   Fri, 18 Jan 2019 13:45:22 +0900
From:   Masami Hiramatsu <mhiramat@...nel.org>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Andreas Ziegler <andreas.ziegler@....de>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org
Subject: [PATCH v2 3/3] tracing: probeevent: Fix to make the type of $comm string

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.

Fixes: 35abb67de744 ("tracing: expose current->comm to [ku]probe events")
Signed-off-by: Masami Hiramatsu <mhiramat@...nel.org>
Cc: stable@...r.kernel.org
---
 kernel/trace/trace_probe.c |   13 +++++++------
 1 file changed, 7 insertions(+), 6 deletions(-)

diff --git a/kernel/trace/trace_probe.c b/kernel/trace/trace_probe.c
index 9962cb5da8ac..44f078cda0ac 100644
--- a/kernel/trace/trace_probe.c
+++ b/kernel/trace/trace_probe.c
@@ -405,13 +405,14 @@ static int traceprobe_parse_probe_arg_body(char *arg, ssize_t *size,
 				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);