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Date:   Wed, 8 Jun 2022 09:40:24 +0200
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Subject: Re: [PATCH 16/36] tty/vt: consolemap: check put_user() in
 con_get_unimap()
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To:     =?UTF-8?Q?Ilpo_J=c3=a4rvinen?= <ilpo.jarvinen@linux.intel.com>
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        linux-serial <linux-serial@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>
References: <20220607104946.18710-1-jslaby@suse.cz>
 <20220607104946.18710-16-jslaby@suse.cz>
 <8ad44d3b-449f-4a30-1a4c-dffd43bbbd1@linux.intel.com>
From:   Jiri Slaby <jirislaby@kernel.org>
In-Reply-To: <8ad44d3b-449f-4a30-1a4c-dffd43bbbd1@linux.intel.com>
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On 07. 06. 22, 16:19, Ilpo Järvinen wrote:
> On Tue, 7 Jun 2022, Jiri Slaby wrote:
> 
>> Only the return value of copy_to_user() is checked in con_get_unimap().
>> Do the same for put_user() of the count too.
>>
>> Signed-off-by: Jiri Slaby <jslaby@suse.cz>
>> ---
>>   drivers/tty/vt/consolemap.c | 3 ++-
>>   1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/tty/vt/consolemap.c b/drivers/tty/vt/consolemap.c
>> index 831450f2bfd1..92b5dddb00d9 100644
>> --- a/drivers/tty/vt/consolemap.c
>> +++ b/drivers/tty/vt/consolemap.c
>> @@ -813,7 +813,8 @@ int con_get_unimap(struct vc_data *vc, ushort ct, ushort __user *uct,
>>   	console_unlock();
>>   	if (copy_to_user(list, unilist, min(ect, ct) * sizeof(*unilist)))
>>   		ret = -EFAULT;
>> -	put_user(ect, uct);
>> +	if (put_user(ect, uct))
>> +		ret = -EFAULT;
>>   	kvfree(unilist);
>>   	return ret ? ret : (ect <= ct) ? 0 : -ENOMEM;
>>   }
>>
> 
> Doesn't this fix something?

If you mean a Fixes tag, this is pre-git.

If you mean a bug, well, likely yes, users now get informed. But I don't 
think anyone cares ;). But who knows, maybe we will start seeing 
userspace failures now (as they might not provide writable count field 
-- unlikely). That's one of the reasons why I did this as a separate 
commit. Let's see if are going to revert this or not...

thanks,
-- 
js
suse labs