linux-kernel - Re: [PATCH 16/36] tty/vt: consolemap: check put_user() in con_get

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Message-ID: <e9f35a26-8f5b-f585-2e8c-19690bf3c770@kernel.org>
Date:   Wed, 8 Jun 2022 09:40:24 +0200
From:   Jiri Slaby <jirislaby@...nel.org>
To:     Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-serial <linux-serial@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 16/36] tty/vt: consolemap: check put_user() in
 con_get_unimap()

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@...e.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