linux-kernel - [PATCH] tracing/probes: Fix MAX_TRACE

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Message-ID: <20240929200939.162524-1-mikel@mikelr.com>
Date: Sun, 29 Sep 2024 16:09:37 -0400
From: Mikel Rychliski <mikel@...elr.com>
To: Steven Rostedt <rostedt@...dmis.org>,
	Masami Hiramatsu <mhiramat@...nel.org>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc: Mikel Rychliski <mikel@...elr.com>,
	linux-kernel@...r.kernel.org,
	linux-trace-kernel@...r.kernel.org
Subject: [PATCH] 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. This
restores the prior behaviour of silently ignoring excess arguments.

Fixes: 035ba76014c0 ("tracing/probes: cleanup: Set trace_probe::nr_args at trace_probe_init")
Signed-off-by: Mikel Rychliski <mikel@...elr.com>
---
 kernel/trace/trace_eprobe.c | 5 +++--
 kernel/trace/trace_fprobe.c | 3 ++-
 kernel/trace/trace_kprobe.c | 3 ++-
 kernel/trace/trace_uprobe.c | 3 ++-
 4 files changed, 9 insertions(+), 5 deletions(-)

diff --git a/kernel/trace/trace_eprobe.c b/kernel/trace/trace_eprobe.c
index b0e0ec85912e..62c1a1fba403 100644
--- a/kernel/trace/trace_eprobe.c
+++ b/kernel/trace/trace_eprobe.c
@@ -914,7 +914,7 @@ static int __trace_eprobe_create(int argc, const char *argv[])
 
 	mutex_lock(&event_mutex);
 	event_call = find_and_get_event(sys_name, sys_event);
-	ep = alloc_event_probe(group, event, event_call, argc - 2);
+	ep = alloc_event_probe(group, event, event_call, min(argc - 2, MAX_TRACE_ARGS));
 	mutex_unlock(&event_mutex);
 
 	if (IS_ERR(ep)) {
@@ -936,8 +936,9 @@ static int __trace_eprobe_create(int argc, const char *argv[])
 		ep->filter_str = NULL;
 
 	argc -= 2; argv += 2;
+	argc = min(argc, MAX_TRACE_ARGS);
 	/* 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)
diff --git a/kernel/trace/trace_fprobe.c b/kernel/trace/trace_fprobe.c
index a079abd8955b..ca72fe8a04e7 100644
--- a/kernel/trace/trace_fprobe.c
+++ b/kernel/trace/trace_fprobe.c
@@ -1187,6 +1187,7 @@ static int __trace_fprobe_create(int argc, const char *argv[])
 		argc = new_argc;
 		argv = new_argv;
 	}
+	argc = min(argc, MAX_TRACE_ARGS);
 
 	ret = traceprobe_expand_dentry_args(argc, argv, &dbuf);
 	if (ret)
@@ -1203,7 +1204,7 @@ 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);
diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c
index 61a6da808203..10d16b574db5 100644
--- a/kernel/trace/trace_kprobe.c
+++ b/kernel/trace/trace_kprobe.c
@@ -1013,6 +1013,7 @@ static int __trace_kprobe_create(int argc, const char *argv[])
 		argc = new_argc;
 		argv = new_argv;
 	}
+	argc = min(argc, MAX_TRACE_ARGS);
 
 	ret = traceprobe_expand_dentry_args(argc, argv, &dbuf);
 	if (ret)
@@ -1029,7 +1030,7 @@ 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);
diff --git a/kernel/trace/trace_uprobe.c b/kernel/trace/trace_uprobe.c
index c3df411a2684..985d23d57702 100644
--- a/kernel/trace/trace_uprobe.c
+++ b/kernel/trace/trace_uprobe.c
@@ -676,6 +676,7 @@ static int __trace_uprobe_create(int argc, const char **argv)
 
 	argc -= 2;
 	argv += 2;
+	argc = min(argc, MAX_TRACE_ARGS);
 
 	tu = alloc_trace_uprobe(group, event, argc, is_return);
 	if (IS_ERR(tu)) {
@@ -690,7 +691,7 @@ 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,
 		};

base-commit: 886f3732878dc92fb0ad6d8b6740b66410d1d50a
-- 
2.46.1