linux-kernel - [PATCH 1/1] radix-tree: Prevent NULL pointer dereference in radix_tree_node_rcu

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Message-ID: <20250223200603.38895-1-ayaanmirzabaig85@gmail.com>
Date: Mon, 24 Feb 2025 01:31:08 +0530
From: Ayaan Mirza Baig <ayaanmirzabaig85@...il.com>
To: linux-kernel@...r.kernel.org
Cc: akpm@...ux-foundation.org,
	ayaanmirzabaig85@...il.com,
	syzbot+80e5d6f453f14a53383a@...kaller.appspotmail.com
Subject: [PATCH 1/1] radix-tree: Prevent NULL pointer dereference in radix_tree_node_rcu_free

syzkaller reported a kernel NULL pointer dereference:

BUG: kernel NULL pointer dereference, address: 0000000000000000
PGD 0 P4D 0
Oops: Oops: 0010 [#1] PREEMPT SMP KASAN NOPTI

Call Trace:
 <IRQ>
 rcu_do_batch kernel/rcu/tree.c:2546 [inline]
 rcu_core+0xaaa/0x17a0 kernel/rcu/tree.c:2802
 handle_softirqs+0x2d4/0x9b0 kernel/softirq.c:561
 __do_softirq kernel/softirq.c:595 [inline]
 invoke_softirq kernel/softirq.c:435 [inline]
 __irq_exit_rcu+0xf7/0x220 kernel/softirq.c:662
 irq_exit_rcu+0x9/0x30 kernel/softirq.c:678
 instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1049 [inline]
 sysvec_apic_timer_interrupt+0xa6/0xc0 arch/x86/kernel/apic/apic.c:1049
 </IRQ>
 <TASK>
 asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:702
RIP: 0010:__raw_spin_unlock_irqrestore include/linux/spinlock_api_smp.h:152 [inline]
RIP: 0010:_raw_spin_unlock_irqrestore+0xd8/0x140 kernel/locking/spinlock.c:194

Reported-by: syzbot+80e5d6f453f14a53383a@...kaller.appspotmail.com

Link: https://syzkaller.appspot.com/bug?extid=80e5d6f453f14a53383a
Signed-off-by: Ayaan Mirza Baig <ayaanmirzabaig85@...il.com>
---
 lib/radix-tree.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/lib/radix-tree.c b/lib/radix-tree.c
index 976b9bd02a1b..5cefbfd7677e 100644
--- a/lib/radix-tree.c
+++ b/lib/radix-tree.c
@@ -292,6 +292,9 @@ void radix_tree_node_rcu_free(struct rcu_head *head)
 	struct radix_tree_node *node =
 			container_of(head, struct radix_tree_node, rcu_head);
 
+	if (unlikely(!node))
+		return; //Prevent NULL deref
+
 	/*
 	 * Must only free zeroed nodes into the slab.  We can be left with
 	 * non-NULL entries by radix_tree_free_nodes, so clear the entries
-- 
2.47.1


Note to reviewers:
I'm new to kernel development and would appreciate feedback on patch
formatting or workflow if I missed any conventions. Thank you for
your patience and guidance.