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Date:   Fri, 21 Aug 2020 11:27:45 -0700
From:   Guenter Roeck <linux@roeck-us.net>
To:     Jason Baron <jbaron@akamai.com>
Cc:     jdelvare@suse.com, linux-hwmon@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH] hwmon: (nct7904) Correct divide by 0
Message-ID: <20200821182745.GA236235@roeck-us.net>
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On Fri, Aug 21, 2020 at 12:20:14PM -0400, Jason Baron wrote:
> We hit a kernel panic due to a divide by 0 in nct7904_read_fan() for
> the hwmon_fan_min case. Extend the check to hwmon_fan_input case as well
> for safety.
> 
> [ 1656.545650] divide error: 0000 [#1] SMP PTI
> [ 1656.545779] CPU: 12 PID: 18010 Comm: sensors Not tainted 5.4.47 #1
> [ 1656.546065] RIP: 0010:nct7904_read+0x1e9/0x510 [nct7904]
> ...
> [ 1656.546549] RAX: 0000000000149970 RBX: ffffbd6b86bcbe08 RCX: 0000000000000000
> ...
> [ 1656.547548] Call Trace:
> [ 1656.547665]  hwmon_attr_show+0x32/0xd0 [hwmon]
> [ 1656.547783]  dev_attr_show+0x18/0x50
> [ 1656.547898]  sysfs_kf_seq_show+0x99/0x120
> [ 1656.548013]  seq_read+0xd8/0x3e0
> [ 1656.548127]  vfs_read+0x89/0x130
> [ 1656.548234]  ksys_read+0x7d/0xb0
> [ 1656.548342]  do_syscall_64+0x48/0x110
> [ 1656.548451]  entry_SYSCALL_64_after_hwframe+0x44/0xa9
> 
> Signed-off-by: Jason Baron <jbaron@akamai.com>

Applied.

Thanks,
Guenter

> ---
>  drivers/hwmon/nct7904.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/hwmon/nct7904.c b/drivers/hwmon/nct7904.c
> index b042569..242ff8b 100644
> --- a/drivers/hwmon/nct7904.c
> +++ b/drivers/hwmon/nct7904.c
> @@ -231,7 +231,7 @@ static int nct7904_read_fan(struct device *dev, u32 attr, int channel,
>  		if (ret < 0)
>  			return ret;
>  		cnt = ((ret & 0xff00) >> 3) | (ret & 0x1f);
> -		if (cnt == 0x1fff)
> +		if (cnt == 0 || cnt == 0x1fff)
>  			rpm = 0;
>  		else
>  			rpm = 1350000 / cnt;
> @@ -243,7 +243,7 @@ static int nct7904_read_fan(struct device *dev, u32 attr, int channel,
>  		if (ret < 0)
>  			return ret;
>  		cnt = ((ret & 0xff00) >> 3) | (ret & 0x1f);
> -		if (cnt == 0x1fff)
> +		if (cnt == 0 || cnt == 0x1fff)
>  			rpm = 0;
>  		else
>  			rpm = 1350000 / cnt;