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Date:   Mon, 11 Oct 2021 10:36:15 +0200
From:   Alexandre Belloni <alexandre.belloni@bootlin.com>
To:     Yang Yingliang <yangyingliang@huawei.com>
Cc:     linux-kernel@vger.kernel.org, linux-rtc@vger.kernel.org,
        a.zummo@towertech.it
Subject: Re: [PATCH 2/2] rtc: class: return error code when cdev_device_add()
 failed
Message-ID: <YWP3f1wPbim8VG6K@piout.net>
References: <20211011080302.1982894-1-yangyingliang@huawei.com>
 <20211011080302.1982894-2-yangyingliang@huawei.com>
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Precedence: bulk

On 11/10/2021 16:03:02+0800, Yang Yingliang wrote:
> I got a null-ptr-deref report when doing fault injection test:
> 
> general protection fault, probably for non-canonical address 0xdffffc0000000022: 0000 [#1] SMP KASAN PTI
> KASAN: null-ptr-deref in range [0x0000000000000110-0x0000000000000117]
> CPU: 1 PID: 1028 Comm: 33 Not tainted 5.15.0-rc3-00111-gf5dad42ed4fe-dirty #481 2a70b3e6ca240b8638beac7ef491cce6183bbec7
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.13.0-1ubuntu1.1 04/01/2014
> RIP: 0010:device_del+0x132/0xdc0
> Code: 48 c1 ea 03 80 3c 02 00 0f 85 4f 0c 00 00 48 b8 00 00 00 00 00 fc ff df 4c 8b 7b 48 4d 8d a7 10 01 00 00 4c 89 e2 48 c1 ea 03 <0f> b6 04 02 84 c0 74 06 0f 8e 7f 0a 00 00 45 0f b6 b7 10 01 00 00
> RSP: 0018:ffffc90002e876b8 EFLAGS: 00010206
> RAX: dffffc0000000000 RBX: ffff88801eb84000 RCX: ffffffff97227644
> RDX: 0000000000000022 RSI: ffff8880146a0000 RDI: 0000000000000002
> RBP: ffff88801eb84120 R08: fffffbfff349a60d R09: fffffbfff349a60d
> R10: ffffc90002e876b8 R11: fffffbfff349a60c R12: 0000000000000110
> R13: 0000000000000001 R14: ffffc90002e87848 R15: 0000000000000000
> FS:  00007fa514973500(0000) GS:ffff888104600000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00007fa51474ccb0 CR3: 000000002bcb0001 CR4: 0000000000770ee0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> PKRU: 55555554
> Call Trace:
>  ? write_comp_data+0x2a/0x90
>  ? cleanup_glue_dir+0x260/0x260
>  ? is_rtc_hctosys.isra.0+0xb9/0xf0
>  ? rtc_proc_show+0x440/0x440
>  ? rcu_read_lock_held_common+0xe/0xa0
>  ? rcu_read_lock_sched_held+0x62/0xe0
>  cdev_device_del+0x1a/0x80
>  devm_rtc_unregister_device+0x37/0x80
>  release_nodes+0xc3/0x3b0
> 
> If cdev_device_add() fails, 'dev->p' is not set, it causes
> null-ptr-deref when calling cdev_device_del(), return error
> code when cdev_device_add() failed to fix this.
> 
> Reported-by: Hulk Robot <hulkci@huawei.com>
> Fixes: 3068a254d5519 ("rtc: introduce new registration method")
> Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>
> ---
>  drivers/rtc/class.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/rtc/class.c b/drivers/rtc/class.c
> index 1f18c39a4b82..76422faee05b 100644
> --- a/drivers/rtc/class.c
> +++ b/drivers/rtc/class.c
> @@ -399,12 +399,14 @@ int __devm_rtc_register_device(struct module *owner, struct rtc_device *rtc)
>  	rtc_dev_prepare(rtc);
>  
>  	err = cdev_device_add(&rtc->char_dev, &rtc->dev);
> -	if (err)
> +	if (err) {
>  		dev_warn(rtc->dev.parent, "failed to add char device %d:%d\n",
>  			 MAJOR(rtc->dev.devt), rtc->id);
> -	else
> +		return err;

As the checkpatch warning indicates, registering the character device as
always been optional. d5ed9177f64fe95d9de79e6504d41612d9127e8a is the
commit you want to fix.

> +	} else {
>  		dev_dbg(rtc->dev.parent, "char device (%d:%d)\n",
>  			MAJOR(rtc->dev.devt), rtc->id);
> +	}
>  
>  	rtc_proc_add_device(rtc);
>  
> -- 
> 2.25.1
> 

-- 
Alexandre Belloni, co-owner and COO, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com