Messages in this thread | | | Subject | Re: [v3] nbd: fix potential NULL pointer fault in nbd_genl_disconnect | From | "sunke (E)" <> | Date | Wed, 12 Feb 2020 10:00:37 +0800 |
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在 2020/2/12 0:39, Mike Christie 写道: > On 02/10/2020 10:12 PM, sunke (E) wrote: >> >> >> 在 2020/2/11 1:05, Mike Christie 写道: >>> On 02/10/2020 01:32 AM, Sun Ke wrote: >>>> Open /dev/nbdX first, the config_refs will be 1 and >>>> the pointers in nbd_device are still null. Disconnect >>>> /dev/nbdX, then reference a null recv_workq. The >>>> protection by config_refs in nbd_genl_disconnect is useless. >>>> >>>> To fix it, just add a check for a non null task_recv in >>>> nbd_genl_disconnect. >>>> >>>> Signed-off-by: Sun Ke <sunke32@huawei.com> >>>> --- >>>> v1 -> v2: >>>> Add an omitted mutex_unlock. >>>> >>>> v2 -> v3: >>>> Add nbd->config_lock, suggested by Josef. >>>> --- >>>> drivers/block/nbd.c | 8 ++++++++ >>>> 1 file changed, 8 insertions(+) >>>> >>>> diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c >>>> index b4607dd96185..870b3fd0c101 100644 >>>> --- a/drivers/block/nbd.c >>>> +++ b/drivers/block/nbd.c >>>> @@ -2008,12 +2008,20 @@ static int nbd_genl_disconnect(struct sk_buff >>>> *skb, struct genl_info *info) >>>> index); >>>> return -EINVAL; >>>> } >>>> + mutex_lock(&nbd->config_lock); >>>> if (!refcount_inc_not_zero(&nbd->refs)) { >>>> + mutex_unlock(&nbd->config_lock); >>>> mutex_unlock(&nbd_index_mutex); >>>> printk(KERN_ERR "nbd: device at index %d is going down\n", >>>> index); >>>> return -EINVAL; >>>> } >>>> + if (!nbd->recv_workq) { >>>> + mutex_unlock(&nbd->config_lock); >>>> + mutex_unlock(&nbd_index_mutex); >>>> + return -EINVAL; >>>> + } >>>> + mutex_unlock(&nbd->config_lock); >>>> mutex_unlock(&nbd_index_mutex); >>>> if (!refcount_inc_not_zero(&nbd->config_refs)) { >>>> nbd_put(nbd); >>>> >>> >>> With my other patch then we will not need this right? It handles your >>> case by just being integrated with the existing checks in: >>> >>> nbd_disconnect_and_put->nbd_clear_sock->sock_shutdown >>> >>> ... >>> >>> static void sock_shutdown(struct nbd_device *nbd) >>> { >>> >>> .... >>> >>> if (config->num_connections == 0) >>> return; >>> >>> >>> num_connections is zero for your case since we never did a >>> nbd_genl_disconnect so we would return here. >>> >>> >>> . >>> >> Hi Mike >> >> Your point is not right totally. >> >> Yes, config->num_connections is 0 and will return in sock_shutdown. Then >> it will back to nbd_disconnect_and_put and do flush_workqueue >> (nbd->recv_workq). >> >> nbd_disconnect_and_put >> ->nbd_clear_sock >> ->sock_shutdown >> ->flush_workqueue >> > > My patch removed that extra flush_workqueue in nbd_disconnect_and_put. > > The idea of the patch was to move the flush calls to when we do > sock_shutdown in the config (connect, disconnect, clear sock) code > paths, because that is the time we know we will need to kill the recv > workers and wait for them to complete so we know they are not still > running when userspace does a new config operation. > Yes, I see.
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