tracing/probes: Limit size of event probe to 3K

[ Upstream commit b2aa3b4 ]

There currently isn't a max limit an event probe can be. One could make an
event greater than PAGE_SIZE, which makes the event useless because if
it's bigger than the max event that can be recorded into the ring buffer,
then it will never be recorded.

A event probe should never need to be greater than 3K, so make that the
max size. As long as the max is less than the max that can be recorded
onto the ring buffer, it should be fine.

Cc: stable@vger.kernel.org
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Acked-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Fixes: 93ccae7 ("tracing/kprobes: Support basic types on dynamic events")
Link: https://patch.msgid.link/20260428122302.706610ba@gandalf.local.home
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
[ adjusted context to place MAX_PROBE_EVENT_SIZE near MAX_STRING_SIZE and appended EVENT_TOO_BIG after NEED_STRING_TYPE ]
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: rostedt

kernel/trace/trace_probe.c

@@ -1366,6 +1366,12 @@ static int traceprobe_parse_probe_arg_body(const char *argv, ssize_t *size,
 	parg->offset = *size;
 	*size += parg->type->size * (parg->count ?: 1);
 
+	if (*size > MAX_PROBE_EVENT_SIZE) {
+		ret = -E2BIG;
+		trace_probe_log_err(ctx->offset, EVENT_TOO_BIG);
+		goto fail;
+	}
+
 	if (parg->count) {
 		len = strlen(parg->type->fmttype) + 6;
 		parg->fmt = kmalloc(len, GFP_KERNEL);

kernel/trace/trace_probe.h

@@ -35,6 +35,7 @@
 #define MAX_ARG_NAME_LEN	32
 #define MAX_BTF_ARGS_LEN	128
 #define MAX_STRING_SIZE		PATH_MAX
+#define MAX_PROBE_EVENT_SIZE	3072
 
 /* Reserved field names */
 #define FIELD_STRING_IP		"__probe_ip"
@@ -546,7 +547,8 @@ extern int traceprobe_define_arg_fields(struct trace_event_call *event_call,
 	C(NO_BTF_FIELD,		"This field is not found."),	\
 	C(BAD_BTF_TID,		"Failed to get BTF type info."),\
 	C(BAD_TYPE4STR,		"This type does not fit for string."),\
-	C(NEED_STRING_TYPE,	"$comm and immediate-string only accepts string type"),
+	C(NEED_STRING_TYPE,	"$comm and immediate-string only accepts string type"),\
+	C(EVENT_TOO_BIG,	"Event too big (too many fields?)"),
 
 #undef C
 #define C(a, b)		TP_ERR_##a