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SubjectRe: [PATCH net] can: raw: fix raw_rcv panic for sock UAF
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On 21.07.21 13:37, Ziyang Xuan (William) wrote:
> On 7/21/2021 5:24 PM, Oliver Hartkopp wrote:

>>
>> Can you please resend the below patch as suggested by Greg KH and add my
>>
>> Signed-off-by: Oliver Hartkopp <socketcan@hartkopp.net>
>>
>> as it also adds the dev_get_by_index() return check.
>>
>> diff --git a/net/can/raw.c b/net/can/raw.c
>> index ed4fcb7ab0c3..d3cbc32036c7 100644
>> --- a/net/can/raw.c
>> +++ b/net/can/raw.c
>> @@ -544,14 +544,18 @@ static int raw_setsockopt(struct socket *sock, int level, int optname,
>>          } else if (count == 1) {
>>              if (copy_from_sockptr(&sfilter, optval, sizeof(sfilter)))
>>                  return -EFAULT;
>>          }
>>
>> +        rtnl_lock();
>>          lock_sock(sk);
>>
>> -        if (ro->bound && ro->ifindex)
>> +        if (ro->bound && ro->ifindex) {
>>              dev = dev_get_by_index(sock_net(sk), ro->ifindex);
>> +            if (!dev)
>> +                goto out_fil;
>> +        }
> At first, I also use this modification. After discussion with my partner, we found that
> it is impossible scenario if we use rtnl_lock to protect net_device object.
> We can see two sequences:
> 1. raw_setsockopt first get rtnl_lock, unregister_netdevice_many later.
> It can be simplified to add the filter in raw_setsockopt, then remove the filter in raw_notify.
>
> 2. unregister_netdevice_many first get rtnl_lock, raw_setsockopt later.
> raw_notify will set ro->ifindex, ro->bound and ro->count to zero firstly. The filter will not
> be added to any filter_list in raw_notify.
>
> So I selected the current modification. Do you think so?
>
> My first modification as following:
>
> diff --git a/net/can/raw.c b/net/can/raw.c
> index ed4fcb7ab0c3..a0ce4908317f 100644
> --- a/net/can/raw.c
> +++ b/net/can/raw.c
> @@ -546,10 +546,16 @@ static int raw_setsockopt(struct socket *sock, int level, int optname,
> return -EFAULT;
> }
>
> + rtnl_lock();
> lock_sock(sk);
>
> - if (ro->bound && ro->ifindex)
> + if (ro->bound && ro->ifindex) {
> dev = dev_get_by_index(sock_net(sk), ro->ifindex);
> + if (!dev) {
> + err = -ENODEV;
> + goto out_fil;
> + }
> + }
>
> if (ro->bound) {
> /* (try to) register the new filters */
> @@ -559,11 +565,8 @@ static int raw_setsockopt(struct socket *sock, int level, int optname,
> else
> err = raw_enable_filters(sock_net(sk), dev, sk,
> filter, count);
> - if (err) {
> - if (count > 1)
> - kfree(filter);
> + if (err)
> goto out_fil;
> - }
>
> /* remove old filter registrations */
> raw_disable_filters(sock_net(sk), dev, sk, ro->filter,
> @@ -584,10 +587,14 @@ static int raw_setsockopt(struct socket *sock, int level, int optname,
> ro->count = count;
>
> out_fil:
> + if (err && count > 1)
> + kfree(filter);
> +

Setting the err variable to -ENODEV is a good idea but I do not like the
movement of kfree(filter).

The kfree() has a tight relation inside the if-statement for ro->bound
which makes it easier to understand.

Regards,
Oliver

ps. your patches have less context than mine. Do you have different
settings for -U<n>, --unified=<n> for 'git diff' ?

> if (dev)
> dev_put(dev);
>
> release_sock(sk);
> + rtnl_unlock();
>
> break;
>
> @@ -600,10 +607,16 @@ static int raw_setsockopt(struct socket *sock, int level, int optname,
>
> err_mask &= CAN_ERR_MASK;
>
> + rtnl_lock();
> lock_sock(sk);
>
> - if (ro->bound && ro->ifindex)
> + if (ro->bound && ro->ifindex) {
> dev = dev_get_by_index(sock_net(sk), ro->ifindex);
> + if (!dev) {
> + err = -ENODEV;
> + goto out_err;
> + }
> + }
>
> /* remove current error mask */
> if (ro->bound) {
> @@ -627,6 +640,7 @@ static int raw_setsockopt(struct socket *sock, int level, int optname,
> dev_put(dev);
>
> release_sock(sk);
> + rtnl_unlock();
>
> break;
>

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