linux-kernel - Re: [PATCH RESEND 2/4] uaccess: Selectively open read or write user access

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Date:   Thu, 2 Apr 2020 10:00:54 +0200
From:   Christophe Leroy <christophe.leroy@....fr>
To:     Kees Cook <keescook@...omium.org>
Cc:     Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>, airlied@...ux.ie,
        daniel@...ll.ch, torvalds@...ux-foundation.org,
        viro@...iv.linux.org.uk, akpm@...ux-foundation.org, hpa@...or.com,
        linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        linux-mm@...ck.org, linux-arch@...r.kernel.org
Subject: Re: [PATCH RESEND 2/4] uaccess: Selectively open read or write user
 access



Le 02/04/2020 à 09:51, Kees Cook a écrit :
> On Thu, Apr 02, 2020 at 07:34:17AM +0000, Christophe Leroy wrote:
>> [...]
>> diff --git a/kernel/compat.c b/kernel/compat.c
>> index 843dd17e6078..705ca7e418c6 100644
>> --- a/kernel/compat.c
>> +++ b/kernel/compat.c
>> @@ -199,7 +199,7 @@ long compat_get_bitmap(unsigned long *mask, const compat_ulong_t __user *umask,
>>   	bitmap_size = ALIGN(bitmap_size, BITS_PER_COMPAT_LONG);
>>   	nr_compat_longs = BITS_TO_COMPAT_LONGS(bitmap_size);
>>   
>> -	if (!user_access_begin(umask, bitmap_size / 8))
>> +	if (!user_write_access_begin(umask, bitmap_size / 8))
> 
> This looks mismatched: should be user_read_access_begin()?

Oops, looks like a copy/paste/modify where I modified the original 
instead of the copy.


> 
>>   		return -EFAULT;
>>   
>>   	while (nr_compat_longs > 1) {
>> @@ -211,11 +211,11 @@ long compat_get_bitmap(unsigned long *mask, const compat_ulong_t __user *umask,
>>   	}
>>   	if (nr_compat_longs)
>>   		unsafe_get_user(*mask, umask++, Efault);
>> -	user_access_end();
>> +	user_read_access_end();
>>   	return 0;
>>   
>>   Efault:
>> -	user_access_end();
>> +	user_read_access_end();
>>   	return -EFAULT;
>>   }
> 
> (These correctly end read access.)
> 
>>   
>> @@ -228,7 +228,7 @@ long compat_put_bitmap(compat_ulong_t __user *umask, unsigned long *mask,
>>   	bitmap_size = ALIGN(bitmap_size, BITS_PER_COMPAT_LONG);
>>   	nr_compat_longs = BITS_TO_COMPAT_LONGS(bitmap_size);
>>   
>> -	if (!user_access_begin(umask, bitmap_size / 8))
>> +	if (!user_read_access_begin(umask, bitmap_size / 8))
> 
> And ..._write_... here?
> 
>>   		return -EFAULT;
>>   
>>   	while (nr_compat_longs > 1) {
>> @@ -239,10 +239,10 @@ long compat_put_bitmap(compat_ulong_t __user *umask, unsigned long *mask,
>>   	}
>>   	if (nr_compat_longs)
>>   		unsafe_put_user((compat_ulong_t)*mask, umask++, Efault);
>> -	user_access_end();
>> +	user_write_access_end();
>>   	return 0;
>>   Efault:
>> -	user_access_end();
>> +	user_write_access_end();
>>   	return -EFAULT;
>>   }
> 
> (These correctly end write access.)
> 
> 
> All the others look correct. With the above fixed:
> 
> Reviewed-by: Kees Cook <keescook@...omium.org>
> 

Thanks
Christophe