linux-kernel - [PATCH] lib/group_cpus: fix NULL pointer dereference from group_cpus

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Message-Id: <20250619082941.3741592-1-yukuai1@huaweicloud.com>
Date: Thu, 19 Jun 2025 16:29:41 +0800
From: Yu Kuai <yukuai1@...weicloud.com>
To: akpm@...ux-foundation.org,
	tglx@...utronix.de,
	john.g.garry@...cle.com,
	axboe@...nel.dk,
	ming.lei@...hat.com
Cc: linux-kernel@...r.kernel.org,
	yukuai3@...wei.com,
	yukuai1@...weicloud.com,
	yi.zhang@...wei.com,
	yangerkun@...wei.com,
	johnny.chenyi@...wei.com
Subject: [PATCH] lib/group_cpus: fix NULL pointer dereference from group_cpus_evenly()

From: Yu Kuai <yukuai3@...wei.com>

While testing null_blk with configfs, echo 0 > poll_queues will trigger
following panic:

BUG: kernel NULL pointer dereference, address: 0000000000000010
Oops: Oops: 0000 [#1] SMP NOPTI
CPU: 27 UID: 0 PID: 920 Comm: bash Not tainted 6.15.0-02023-gadbdb95c8696-dirty #1238 PREEMPT(undef)
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.1-2.fc37 04/01/2014
RIP: 0010:__bitmap_or+0x48/0x70
Call Trace:
 <TASK>
 __group_cpus_evenly+0x822/0x8c0
 group_cpus_evenly+0x2d9/0x490
 blk_mq_map_queues+0x1e/0x110
 null_map_queues+0xc9/0x170 [null_blk]
 blk_mq_update_queue_map+0xdb/0x160
 blk_mq_update_nr_hw_queues+0x22b/0x560
 nullb_update_nr_hw_queues+0x71/0xf0 [null_blk]
 nullb_device_poll_queues_store+0xa4/0x130 [null_blk]
 configfs_write_iter+0x109/0x1d0
 vfs_write+0x26e/0x6f0
 ksys_write+0x79/0x180
 __x64_sys_write+0x1d/0x30
 x64_sys_call+0x45c4/0x45f0
 do_syscall_64+0xa5/0x240
 entry_SYSCALL_64_after_hwframe+0x76/0x7e

Root cause is that numgrps is set to 0, and ZERO_SIZE_PTR is returned
from kcalloc(), then __group_cpus_evenly() will deference the
ZERO_SIZE_PTR.

Fix the problem by checking kcalloc() return value with ZERO_OR_NULL_PTR,
and NULL will be returned to caller.

Fixes: 6a6dcae8f486 ("blk-mq: Build default queue map via group_cpus_evenly()")
Signed-off-by: Yu Kuai <yukuai3@...wei.com>
---
 lib/group_cpus.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/lib/group_cpus.c b/lib/group_cpus.c
index ee272c4cefcc..5e243946ee4e 100644
--- a/lib/group_cpus.c
+++ b/lib/group_cpus.c
@@ -363,7 +363,7 @@ struct cpumask *group_cpus_evenly(unsigned int numgrps)
 		goto fail_npresmsk;
 
 	masks = kcalloc(numgrps, sizeof(*masks), GFP_KERNEL);
-	if (!masks)
+	if (ZERO_OR_NULL_PTR(masks))
 		goto fail_node_to_cpumask;
 
 	build_node_to_cpumask(node_to_cpumask);
-- 
2.39.2