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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives
Hash Suite for Android: free password hash cracker in your pocket
[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <4292b59f-7956-4c37-8909-ecb2261687b1@davidwei.uk>
Date: Thu, 14 Nov 2024 19:04:46 -0800
From: David Wei <dw@...idwei.uk>
To: Luiz Augusto von Dentz <luiz.dentz@...il.com>
Cc: Michal Luczaj <mhal@...x.co>, 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 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:
>>>>> The bt_copy_from_sockptr() return value is being misinterpreted by most
>>>>> users: a non-zero result is mistakenly assumed to represent an error code,
>>>>> but actually indicates the number of bytes that could not be copied.
>>>>>
>>>>> Remove bt_copy_from_sockptr() and adapt callers to use
>>>>> copy_safe_from_sockptr().
>>>>>
>>>>> For sco_sock_setsockopt() (case BT_CODEC) use copy_struct_from_sockptr() to
>>>>> scrub parts of uninitialized buffer.
>>>>>
>>>>> Opportunistically, rename `len` to `optlen` in hci_sock_setsockopt_old()
>>>>> and hci_sock_setsockopt().
>>>>>
>>>>> Fixes: 51eda36d33e4 ("Bluetooth: SCO: Fix not validating setsockopt user input")
>>>>> Fixes: a97de7bff13b ("Bluetooth: RFCOMM: Fix not validating setsockopt user input")
>>>>> Fixes: 4f3951242ace ("Bluetooth: L2CAP: Fix not validating setsockopt user input")
>>>>> Fixes: 9e8742cdfc4b ("Bluetooth: ISO: Fix not validating setsockopt user input")
>>>>> Fixes: b2186061d604 ("Bluetooth: hci_sock: Fix not validating setsockopt user input")
>>>>> Signed-off-by: Michal Luczaj <mhal@...x.co>
>>>>> ---
>>>>>  include/net/bluetooth/bluetooth.h |  9 ---------
>>>>>  net/bluetooth/hci_sock.c          | 14 +++++++-------
>>>>>  net/bluetooth/iso.c               | 10 +++++-----
>>>>>  net/bluetooth/l2cap_sock.c        | 20 +++++++++++---------
>>>>>  net/bluetooth/rfcomm/sock.c       |  9 ++++-----
>>>>>  net/bluetooth/sco.c               | 11 ++++++-----
>>>>>  6 files changed, 33 insertions(+), 40 deletions(-)
>>>>>
>>>> ...
>>>>> 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.

> 
>> And copy_from_user() follows the same 0 for success or N > 0 for
>> failure. It does not EFAULT on its own AFAIK.
>>
>> The docs for copy_safe_from_sockptr() that you've linked contains the
>> exact misunderstanding that Michal is correcting.
>>
>>>
>>>> Shouldn't this be:
>>>>
>>>> err = -EFAULT;
>>>> if (copy_safe_from_sockptr(&opt, sizeof(opt), optval, optlen))
>>>>         break;
>>>
>>>
>>>
> 
> 
>