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Thu, 19 Jun 2025 05:31:46 -0400 X-MC-Unique: _XqqMhXSOeqXAk9UBgG21A-1 X-Mimecast-MFC-AGG-ID: _XqqMhXSOeqXAk9UBgG21A_1750325504 Received: from mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.93]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-06.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 27B57180028E; Thu, 19 Jun 2025 09:31:44 +0000 (UTC) Received: from fedora (unknown [10.72.116.16]) by mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 04124180035C; Thu, 19 Jun 2025 09:31:36 +0000 (UTC) Date: Thu, 19 Jun 2025 17:31:31 +0800 From: Ming Lei To: Yu Kuai Cc: akpm@linux-foundation.org, tglx@linutronix.de, john.g.garry@oracle.com, axboe@kernel.dk, linux-kernel@vger.kernel.org, yukuai3@huawei.com, yi.zhang@huawei.com, yangerkun@huawei.com, johnny.chenyi@huawei.com Subject: Re: [PATCH] lib/group_cpus: fix NULL pointer dereference from group_cpus_evenly() Message-ID: References: <20250619082941.3741592-1-yukuai1@huaweicloud.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250619082941.3741592-1-yukuai1@huaweicloud.com> X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.93 On Thu, Jun 19, 2025 at 04:29:41PM +0800, Yu Kuai wrote: > From: Yu Kuai > > 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: > > __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 > --- > 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; I'd suggest to check 'numgrps' explicitly, which is more readable than ZERO_PTR. Thanks, Ming