linux-kernel - Re: [PATCH] FS, NET: Fix KMSAN uninit-value in vfs

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Date:   Tue, 14 Mar 2023 20:23:47 +0100
From:   Oliver Hartkopp <socketcan@...tkopp.net>
To:     Ivan Orlov <ivan.orlov0322@...il.com>, mkl@...gutronix.de,
        davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org,
        pabeni@...hat.com
Cc:     linux-can@...r.kernel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, himadrispandya@...il.com,
        skhan@...uxfoundation.org,
        syzbot+c9bfd85eca611ebf5db1@...kaller.appspotmail.com
Subject: Re: [PATCH] FS, NET: Fix KMSAN uninit-value in vfs_write



On 14.03.23 16:37, Ivan Orlov wrote:
> On 3/14/23 18:38, Oliver Hartkopp wrote:
>> Hello Ivan,
>>
>> besides the fact that we would read some uninitialized value the 
>> outcome of the original implementation would have been an error and a 
>> termination of the copy process too. Maybe throwing a different error 
>> number.
>>
>> But it is really interesting to see what KMSAN is able to detect these 
>> days! Many thanks for the finding and your effort to contribute this fix!
>>
>> Best regards,
>> Oliver
>>
>>
>> On 14.03.23 13:04, Ivan Orlov wrote:
>>> Syzkaller reported the following issue:
>>
>> (..)
>>
>>>
>>> Reported-by: syzbot+c9bfd85eca611ebf5db1@...kaller.appspotmail.com
>>> Link: 
>>> https://syzkaller.appspot.com/bug?id=47f897f8ad958bbde5790ebf389b5e7e0a345089
>>> Signed-off-by: Ivan Orlov <ivan.orlov0322@...il.com>
>>
>> Acked-by: Oliver Hartkopp <socketcan@...tkopp.net>
>>
>>
>>> ---
>>>   net/can/bcm.c | 16 ++++++++++------
>>>   1 file changed, 10 insertions(+), 6 deletions(-)
>>>
>>> diff --git a/net/can/bcm.c b/net/can/bcm.c
>>> index 27706f6ace34..a962ec2b8ba5 100644
>>> --- a/net/can/bcm.c
>>> +++ b/net/can/bcm.c
>>> @@ -941,6 +941,8 @@ static int bcm_tx_setup(struct bcm_msg_head 
>>> *msg_head, struct msghdr *msg,
>>>               cf = op->frames + op->cfsiz * i;
>>>               err = memcpy_from_msg((u8 *)cf, msg, op->cfsiz);
>>> +            if (err < 0)
>>> +                goto free_op;
>>>               if (op->flags & CAN_FD_FRAME) {
>>>                   if (cf->len > 64)
>>> @@ -950,12 +952,8 @@ static int bcm_tx_setup(struct bcm_msg_head 
>>> *msg_head, struct msghdr *msg,
>>>                       err = -EINVAL;
>>>               }
>>> -            if (err < 0) {
>>> -                if (op->frames != &op->sframe)
>>> -                    kfree(op->frames);
>>> -                kfree(op);
>>> -                return err;
>>> -            }
>>> +            if (err < 0)
>>> +                goto free_op;
>>>               if (msg_head->flags & TX_CP_CAN_ID) {
>>>                   /* copy can_id into frame */
>>> @@ -1026,6 +1024,12 @@ static int bcm_tx_setup(struct bcm_msg_head 
>>> *msg_head, struct msghdr *msg,
>>>           bcm_tx_start_timer(op);
>>>       return msg_head->nframes * op->cfsiz + MHSIZ;
>>> +
>>> +free_op:
>>> +    if (op->frames != &op->sframe)
>>> +        kfree(op->frames);
>>> +    kfree(op);
>>> +    return err;
>>>   }
>>>   /*
> 
> Thank you for the quick answer! I totally agree that this patch will not 
> change the behavior a lot. However, I think a little bit more error 
> processing will not be bad (considering this will not bring any 
> performance overhead). If someone in the future tries to use the "cf" 
> object right after "memcpy_from_msg" call without proper error 
> processing it will lead to a bug (which will be hard to trigger). Maybe 
> fixing it now to avoid possible future mistakes in the future makes sense?

Yes! Definitely!

Therefore I added my Acked-by: tag. Marc will likely pick this patch for 
upstream.

Best regards,
Oliver