linux-kernel - [PATCH v2] bpf: fix NULL pointer dereference in print_reg

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Message-ID: <20250923174738.1713751-1-listout@listout.xyz>
Date: Tue, 23 Sep 2025 23:17:38 +0530
From: Brahmajit Das <listout@...tout.xyz>
To: syzbot+d36d5ae81e1b0a53ef58@...kaller.appspotmail.com
Cc: 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 v2] 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 | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/bpf/log.c b/kernel/bpf/log.c
index f50533169cc3..5ffb8d778b92 100644
--- a/kernel/bpf/log.c
+++ b/kernel/bpf/log.c
@@ -704,7 +704,7 @@ static void print_reg_state(struct bpf_verifier_env *env,
 		verbose_a("ref_obj_id=%d", reg->ref_obj_id);
 	if (type_is_non_owning_ref(reg->type))
 		verbose_a("%s", "non_own_ref");
-	if (type_is_map_ptr(t)) {
+	if (type_is_map_ptr(t) && reg->map_ptr) {
 		if (reg->map_ptr->name[0])
 			verbose_a("map=%s", reg->map_ptr->name);
 		verbose_a("ks=%d,vs=%d",
-- 
2.51.0