Re: [PATCH] sparc: copy_from_user() should not return -EFAULT

[David Miller]

From: Andi Kleen <andi@xxxxxxxxxxxxxx>
Date: Tue, 05 Jan 2010 18:27:18 +0100

> Heiko Carstens <heiko.carstens@xxxxxxxxxx> writes:
> 
>> Subject: [PATCH] sparc: copy_from_user() should not return -EFAULT
>>
>> From: Heiko Carstens <heiko.carstens@xxxxxxxxxx>
>>
>> Callers of copy_from_user() expect it to return the number of bytes
>> it could not copy. In no case it is supposed to return -EFAULT.
>>
>> In case of a detected buffer overflow just return the requested
>> length. In addition one could think of a memset that would clear
>> the size of the target object.
> 
> Ouch! I would expect this is likely exploitable, e.g. in mount

You can rest easy as the problem only exists in 2.6.33-rcX, it got
introduced when I ported over the compile time length validation bits
from x86.
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