[PATCH v4 07/15] tracing/filters: Reject empty unquoted operand in function event filter

["Masami Hiramatsu (Google)" <mhiramat@kernel.org>]

From: Masami Hiramatsu (Google) <mhiramat@kernel.org>

In parse_pred(), when parsing an unquoted operand for function events,
if the filter expression has no operand before a delimiter (e.g.
'(ip == )' or '(ip == && x == 1)'), the loop terminates with len == 0.

While an empty quoted string (e.g. 'ip == ""') is syntactically valid
and denotes an empty pattern, an unquoted empty operand is a syntax
error where an operand was expected before the delimiter. Previously,
this accepted the predicate with an empty pattern.

Reject empty unquoted operands by checking '!q && !len' and reporting
FILT_ERR_INVALID_VALUE.

Fixes: 80765597bc58 ("tracing: Rewrite filter logic to be simpler and faster")
Cc: stable@vger.kernel.org
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
---
Changes in v3:
 - Split from the monolithic function event parsing patch into a
   standalone patch rejecting empty unquoted operands (!q && !len).
---
 kernel/trace/trace_events_filter.c |    4 ++++
 1 file changed, 4 insertions(+)

diff --git a/kernel/trace/trace_events_filter.c b/kernel/trace/trace_events_filter.c
index 05579895c810..a645af9eb1f8 100644
--- a/kernel/trace/trace_events_filter.c
+++ b/kernel/trace/trace_events_filter.c
@@ -1880,6 +1880,10 @@ static int parse_pred(const char *str, void *data,
 		len = i - s;
 		if (q)
 			i++;
+		if (!q && !len) {
+			parse_error(pe, FILT_ERR_INVALID_VALUE, pos + i);
+			goto err_free;
+		}
 		if (len >= MAX_FILTER_STR_VAL) {
 			parse_error(pe, FILT_ERR_OPERAND_TOO_LONG, pos + i);
 			goto err_free;