linux-kernel - [PATCH 1/1] bpf: fix NULL pointer dereference in print_reg

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Message-ID: <20250923164144.1573636-1-listout@listout.xyz>
Date: Tue, 23 Sep 2025 22:11:44 +0530
From: Brahmajit Das <listout@...tout.xyz>
To: syzbot+d36d5ae81e1b0a53ef58@...kaller.appspotmail.com
Cc: listout@...tout.xyz,
	andrii@...nel.org,
	ast@...nel.org,
	bpf@...r.kernel.org,
	daniel@...earbox.net,
	eddyz87@...il.com,
	haoluo@...gle.com,
	john.fastabend@...il.com,
	jolsa@...nel.org,
	kpsingh@...nel.org,
	linux-kernel@...r.kernel.org,
	martin.lau@...ux.dev,
	sdf@...ichev.me,
	song@...nel.org,
	syzkaller-bugs@...glegroups.com,
	yonghong.song@...ux.dev
Subject: [PATCH 1/1] bpf: fix NULL pointer dereference in print_reg_state()

Syzkaller reported a general protection fault due to a NULL pointer
dereference in print_reg_state() when accessing reg->map_ptr without
checking if it is NULL.

The existing code assumes reg->map_ptr is always valid before
dereferencing reg->map_ptr->name, reg->map_ptr->key_size, and
reg->map_ptr->value_size.

Fix this by adding explicit NULL checks before accessing reg->map_ptr
and its members. This prevents crashes when reg->map_ptr is NULL,
improving the robustness of the BPF verifier's verbose logging.

Reported-by: syzbot+d36d5ae81e1b0a53ef58@...kaller.appspotmail.com
Signed-off-by: Brahmajit Das <listout@...tout.xyz>
---
 kernel/bpf/log.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/kernel/bpf/log.c b/kernel/bpf/log.c
index 38050f4ee400..a2368b21486a 100644
--- a/kernel/bpf/log.c
+++ b/kernel/bpf/log.c
@@ -3,6 +3,7 @@
  * Copyright (c) 2016 Facebook
  * Copyright (c) 2018 Covalent IO, Inc. http://covalent.io
  */
+#include "linux/printk.h"
 #include <uapi/linux/btf.h>
 #include <linux/kernel.h>
 #include <linux/types.h>
@@ -716,11 +717,12 @@ static void print_reg_state(struct bpf_verifier_env *env,
 	if (type_is_non_owning_ref(reg->type))
 		verbose_a("%s", "non_own_ref");
 	if (type_is_map_ptr(t)) {
-		if (reg->map_ptr->name[0])
+		if (reg->map_ptr != NULL && reg->map_ptr->name[0] != '\0')
 			verbose_a("map=%s", reg->map_ptr->name);
-		verbose_a("ks=%d,vs=%d",
-			  reg->map_ptr->key_size,
-			  reg->map_ptr->value_size);
+		if (reg->map_ptr != NULL)
+			verbose_a("ks=%d,vs=%d",
+					reg->map_ptr->key_size,
+					reg->map_ptr->value_size);
 	}
 	if (t != SCALAR_VALUE && reg->off) {
 		verbose_a("off=");
-- 
2.51.0