netdev - Re: [PATCH net 1/4] bluetooth: Improve setsockopt() handling of malformed user input

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Message-ID: <02c01b54-ad82-4ae0-b4fd-db1b7687efa0@rbox.co>
Date: Fri, 15 Nov 2024 09:31:37 +0100
From: Michal Luczaj <mhal@...x.co>
To: David Wei <dw@...idwei.uk>, Luiz Augusto von Dentz <luiz.dentz@...il.com>
Cc: Marcel Holtmann <marcel@...tmann.org>,
 Johan Hedberg <johan.hedberg@...il.com>,
 "David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>,
 Paolo Abeni <pabeni@...hat.com>, Simon Horman <horms@...nel.org>,
 David Howells <dhowells@...hat.com>, Marc Dionne <marc.dionne@...istor.com>,
 Luiz Augusto von Dentz <luiz.von.dentz@...el.com>,
 linux-bluetooth@...r.kernel.org, netdev@...r.kernel.org,
 linux-afs@...ts.infradead.org, Jakub Kicinski <kuba@...nel.org>
Subject: Re: [PATCH net 1/4] bluetooth: Improve setsockopt() handling of
 malformed user input

On 11/15/24 04:04, David Wei wrote:
> On 2024-11-14 18:50, Luiz Augusto von Dentz wrote:
>> Hi David,
>> On Thu, Nov 14, 2024 at 9:30 PM David Wei <dw@...idwei.uk> wrote:
>>> On 2024-11-14 18:15, Luiz Augusto von Dentz wrote:
>>>> Hi David,
>>>> On Thu, Nov 14, 2024 at 7:42 PM David Wei <dw@...idwei.uk> wrote:
>>>>> On 2024-11-14 15:27, Michal Luczaj wrote:
>>>>> ...
>>>>>> diff --git a/net/bluetooth/rfcomm/sock.c b/net/bluetooth/rfcomm/sock.c
>>>>>> index f48250e3f2e103c75d5937e1608e43c123aa3297..1001fb4cc21c0ecc7bcdd3ea9041770ede4f27b8 100644
>>>>>> --- a/net/bluetooth/rfcomm/sock.c
>>>>>> +++ b/net/bluetooth/rfcomm/sock.c
>>>>>> @@ -629,10 +629,9 @@ static int rfcomm_sock_setsockopt_old(struct socket *sock, int optname,
>>>>>>
>>>>>>       switch (optname) {
>>>>>>       case RFCOMM_LM:
>>>>>> -             if (bt_copy_from_sockptr(&opt, sizeof(opt), optval, optlen)) {
>>>>>> -                     err = -EFAULT;
>>>>>> +             err = copy_safe_from_sockptr(&opt, sizeof(opt), optval, optlen);
>>>>>> +             if (err)
>>>>>>                       break;
>>>>>> -             }
>>>>>
>>>>> This will return a positive integer if copy_safe_from_sockptr() fails.
>>>>
>>>> What are you talking about copy_safe_from_sockptr never returns a
>>>> positive value:
>>>>
>>>>  * Returns:
>>>>  *  * -EINVAL: @optlen < @ksize
>>>>  *  * -EFAULT: access to userspace failed.
>>>>  *  * 0 : @ksize bytes were copied
>>>
>>> Isn't this what this series is about? copy_from_sockptr() returns 0 on
>>> success, or a positive integer for number of bytes NOT copied on error.
>>> Patch 4 even updates the docs for copy_from_sockptr().
>>>
>>> copy_safe_from_sockptr()
>>>         -> copy_from_sockptr()
>>>         -> copy_from_sockptr_offset()
>>>         -> memcpy() for kernel to kernel OR
>>>         -> copy_from_user() otherwise
>>
>> Well except the safe version does check what would otherwise cause a
>> positive return by the likes of copy_from_user and returns -EINVAL
>> instead, otherwise the documentation of copy_safe_from_sockptr is just
>> wrong and shall state that it could return positive as well but I
>> guess that would just make it as inconvenient so we might as well
>> detect when a positive value would be returned just return -EFAULT
>> instead.
> 
> Yes it checks and returns EINVAL, but not EFAULT which is what my
> comment on the original patch is about. Most of the calls to
> bt_copy_from_sockptr() that Michal replaced with
> copy_safe_from_sockptr() remain incorrect because it is assumed that
> EFAULT is returned. Only rfcomm_sock_setsockopt_old() was vaguely doing
> the right thing and the patch changed it back to the incorrect pattern:
> 
> err = copy_safe_from_sockptr(...);
> if (err)
> 	break;
> 
> But I do agree that making copy_safe_from_sockptr() do the right thing
> and EFAULT will be easier and prevent future problems given that
> copy_from_sockptr() is meant to be deprecated anyhow.

Just to be clear: copy_safe_from_sockptr() was recently fixed to return
EFAULT:
https://git.kernel.org/pub/scm/linux/kernel/git/netdev/net.git/commit/?id=eb94b7bb1010
Sorry, I should have mentioned this series is a follow up to that patch.

Thanks,
Michal