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

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Message-ID: <68d2d480.a70a0220.1b52b.02b4.GAE@google.com>
Date: Tue, 23 Sep 2025 10:10:24 -0700
From: syzbot <syzbot+d36d5ae81e1b0a53ef58@...kaller.appspotmail.com>
To: linux-kernel@...r.kernel.org
Subject: Forwarded: [PATCH] bpf: fix NULL pointer dereference in print_reg_state()

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***

Subject: [PATCH] bpf: fix NULL pointer dereference in print_reg_state()
Author: listout@...tout.xyz

#syz test

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 | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/kernel/bpf/log.c b/kernel/bpf/log.c
index 38050f4ee400..14c0a442a85b 100644
--- a/kernel/bpf/log.c
+++ b/kernel/bpf/log.c
@@ -715,11 +715,10 @@ 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",
-			  reg->map_ptr->key_size,
+		verbose_a("ks=%d,vs=%d", reg->map_ptr->key_size,
 			  reg->map_ptr->value_size);
 	}
 	if (t != SCALAR_VALUE && reg->off) {
-- 
2.51.0