tracing: Check for no filter when processing event filters

The syzkaller detected a out-of-bounds issue with the events filter code,
specifically here:

	prog[N].pred = NULL;					/* #13 */
	prog[N].target = 1;		/* TRUE */
	prog[N+1].pred = NULL;
	prog[N+1].target = 0;		/* FALSE */
->	prog[N-1].target = N;
	prog[N-1].when_to_branch = false;

As that's the first reference to a "N-1" index, it appears that the code got
here with N = 0, which means the filter parser found no filter to parse
(which shouldn't ever happen, but apparently it did).

Add a new error to the parsing code that will check to make sure that N is
not zero before going into this part of the code. If N = 0, then -EINVAL is
returned, and a error message is added to the filter.

Cc: stable@vger.kernel.org
Fixes: 80765597bc587 ("tracing: Rewrite filter logic to be simpler and faster")
Reported-by: air icy <icytxw@gmail.com>
bugzilla url: https://bugzilla.kernel.org/show_bug.cgi?id=200019
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

diff --git a/kernel/trace/trace_events_filter.c b/kernel/trace/trace_events_filter.c
index e1c818d..0dceb77 100644 (file)
--- a/kernel/trace/trace_events_filter.c
+++ b/kernel/trace/trace_events_filter.c
@@ -78,7 +78,8 @@ static const char * ops[] = { OPS };
        C(TOO_MANY_PREDS,       "Too many terms in predicate expression"), \
        C(INVALID_FILTER,       "Meaningless filter expression"),       \
        C(IP_FIELD_ONLY,        "Only 'ip' field is supported for function trace"), \
-       C(INVALID_VALUE,        "Invalid value (did you forget quotes)?"),
+       C(INVALID_VALUE,        "Invalid value (did you forget quotes)?"), \
+       C(NO_FILTER,            "No filter found"),
 
 #undef C
 #define C(a, b)                FILT_ERR_##a
@@ -550,6 +551,13 @@ predicate_parse(const char *str, int nr_parens, int nr_preds,
                goto out_free;
        }
 
+       if (!N) {
+               /* No program? */
+               ret = -EINVAL;
+               parse_error(pe, FILT_ERR_NO_FILTER, ptr - str);
+               goto out_free;
+       }
+
        prog[N].pred = NULL;                                    /* #13 */
        prog[N].target = 1;             /* TRUE */
        prog[N+1].pred = NULL;