tracing: probeevent: Fix to make the type of $comm string

BugLink: https://bugs.launchpad.net/bugs/1837516
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@fau.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: stable@vger.kernel.org
Fixes: 533059281ee5 ("tracing: probeevent: Introduce new argument fetching code")
Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>

diff --git a/kernel/trace/trace_probe.c b/kernel/trace/trace_probe.c
index 9962cb5da8acdebb43e247c1e55df86a19038a51..44f078cda0ac84e0a519659a061fee6027df55c2 100644 (file)
--- 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);