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

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Message-ID: <970c7945-3dc4-4f07-94d5-19080efb2f21@davidwei.uk>
Date: Thu, 14 Nov 2024 18:30:53 -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 18:15, 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

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;
> 
> 
>