tracing/probes: Fix MAX_TRACE_ARGS limit handling

When creating a trace_probe we would set nr_args prior to truncating the
arguments to MAX_TRACE_ARGS. However, we would only initialize arguments
up to the limit.

This caused invalid memory access when attempting to set up probes with
more than 128 fetchargs.

  BUG: kernel NULL pointer dereference, address: 0000000000000020
  #PF: supervisor read access in kernel mode
  #PF: error_code(0x0000) - not-present page
  PGD 0 P4D 0
  Oops: Oops: 0000 [#1] PREEMPT SMP PTI
  CPU: 0 UID: 0 PID: 1769 Comm: cat Not tainted 6.11.0-rc7+ #8
  Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.3-1.fc39 04/01/2014
  RIP: 0010:__set_print_fmt+0x134/0x330

Resolve the issue by applying the MAX_TRACE_ARGS limit earlier. Return
an error when there are too many arguments instead of silently
truncating.

Link: https://lore.kernel.org/all/20240930202656.292869-1-mikel@mikelr.com/

Fixes: 035ba76 ("tracing/probes: cleanup: Set trace_probe::nr_args at trace_probe_init")
Signed-off-by: Mikel Rychliski <mikel@mikelr.com>
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>

Author: mikelr

kernel/trace/trace_eprobe.c

@@ -912,6 +912,11 @@ static int __trace_eprobe_create(int argc, const char *argv[])
 		}
 	}
 
+	if (argc - 2 > MAX_TRACE_ARGS) {
+		ret = -E2BIG;
+		goto error;
+	}
+
 	mutex_lock(&event_mutex);
 	event_call = find_and_get_event(sys_name, sys_event);
 	ep = alloc_event_probe(group, event, event_call, argc - 2);
@@ -937,7 +942,7 @@ static int __trace_eprobe_create(int argc, const char *argv[])
 
 	argc -= 2; argv += 2;
 	/* parse arguments */
-	for (i = 0; i < argc && i < MAX_TRACE_ARGS; i++) {
+	for (i = 0; i < argc; i++) {
 		trace_probe_log_set_index(i + 2);
 		ret = trace_eprobe_tp_update_arg(ep, argv, i);
 		if (ret)

kernel/trace/trace_fprobe.c

@@ -1187,6 +1187,10 @@ static int __trace_fprobe_create(int argc, const char *argv[])
 		argc = new_argc;
 		argv = new_argv;
 	}
+	if (argc > MAX_TRACE_ARGS) {
+		ret = -E2BIG;
+		goto out;
+	}
 
 	ret = traceprobe_expand_dentry_args(argc, argv, &dbuf);
 	if (ret)
@@ -1203,7 +1207,7 @@ static int __trace_fprobe_create(int argc, const char *argv[])
 	}
 
 	/* parse arguments */
-	for (i = 0; i < argc && i < MAX_TRACE_ARGS; i++) {
+	for (i = 0; i < argc; i++) {
 		trace_probe_log_set_index(i + 2);
 		ctx.offset = 0;
 		ret = traceprobe_parse_probe_arg(&tf->tp, i, argv[i], &ctx);

kernel/trace/trace_kprobe.c

@@ -1013,6 +1013,10 @@ static int __trace_kprobe_create(int argc, const char *argv[])
 		argc = new_argc;
 		argv = new_argv;
 	}
+	if (argc > MAX_TRACE_ARGS) {
+		ret = -E2BIG;
+		goto out;
+	}
 
 	ret = traceprobe_expand_dentry_args(argc, argv, &dbuf);
 	if (ret)
@@ -1029,7 +1033,7 @@ static int __trace_kprobe_create(int argc, const char *argv[])
 	}
 
 	/* parse arguments */
-	for (i = 0; i < argc && i < MAX_TRACE_ARGS; i++) {
+	for (i = 0; i < argc; i++) {
 		trace_probe_log_set_index(i + 2);
 		ctx.offset = 0;
 		ret = traceprobe_parse_probe_arg(&tk->tp, i, argv[i], &ctx);

kernel/trace/trace_uprobe.c

@@ -565,6 +565,8 @@ static int __trace_uprobe_create(int argc, const char **argv)
 
 	if (argc < 2)
 		return -ECANCELED;
+	if (argc - 2 > MAX_TRACE_ARGS)
+		return -E2BIG;
 
 	if (argv[0][1] == ':')
 		event = &argv[0][2];
@@ -690,7 +692,7 @@ static int __trace_uprobe_create(int argc, const char **argv)
 	tu->filename = filename;
 
 	/* parse arguments */
-	for (i = 0; i < argc && i < MAX_TRACE_ARGS; i++) {
+	for (i = 0; i < argc; i++) {
 		struct traceprobe_parse_context ctx = {
 			.flags = (is_return ? TPARG_FL_RETURN : 0) | TPARG_FL_USER,
 		};