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

[Masami Hiramatsu]

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 <mhira...@kernel.org>
Cc: sta...@vger.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);