Re: [dpdk-dev] [PATCH v6 07/19] vhost: add number of fds to vhost-user messages and use it

[Ilya Maximets <i.maximets@samsung.com>]

On 12.10.2018 11:57, Maxime Coquelin wrote:
> 
> 
> On 10/12/2018 10:45 AM, Maxime Coquelin wrote:
>>
>>
>> On 10/12/2018 10:43 AM, Maxime Coquelin wrote:
>>>
>>>
>>> On 10/11/2018 05:59 PM, Ilya Maximets wrote:
>>>> On 11.10.2018 12:24, Maxime Coquelin wrote:
>>>>> As soon as some ancillary data (fds) are received, it is copied
>>>>> without checking its length.
>>>>>
>>>>> This patch adds the number of fds received to the message,
>>>>> which is set in read_vhost_message().
>>>>>
>>>>> This is preliminary work to support sending fds to Qemu.
>>>>>
>>>>> Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
>>>>> Signed-off-by: Maxime Coquelin <maxime.coquelin@redhat.com>
>>>>> ---
>>>>>   lib/librte_vhost/socket.c     | 25 ++++++++++++++++++++-----
>>>>>   lib/librte_vhost/vhost_user.c |  2 +-
>>>>>   lib/librte_vhost/vhost_user.h |  4 +++-
>>>>>   3 files changed, 24 insertions(+), 7 deletions(-)
>>>>>
>>>>> diff --git a/lib/librte_vhost/socket.c b/lib/librte_vhost/socket.c
>>>>> index d63031747..3b0287a26 100644
>>>>> --- a/lib/librte_vhost/socket.c
>>>>> +++ b/lib/librte_vhost/socket.c
>>>>> @@ -94,18 +94,24 @@ static struct vhost_user vhost_user = {
>>>>>       .mutex = PTHREAD_MUTEX_INITIALIZER,
>>>>>   };
>>>>> -/* return bytes# of read on success or negative val on failure. */
>>>>> +/*
>>>>> + * return bytes# of read on success or negative val on failure. Update fdnum
>>>>> + * with number of fds read.
>>>>> + */
>>>>>   int
>>>>> -read_fd_message(int sockfd, char *buf, int buflen, int *fds, int fd_num)
>>>>> +read_fd_message(int sockfd, char *buf, int buflen, int *fds, int max_fds,
>>>>> +        int *fd_num)
>>>>>   {
>>>>>       struct iovec iov;
>>>>>       struct msghdr msgh;
>>>>> -    size_t fdsize = fd_num * sizeof(int);
>>>>> -    char control[CMSG_SPACE(fdsize)];
>>>>> +    char control[CMSG_SPACE(max_fds * sizeof(int))];
>>>>>       struct cmsghdr *cmsg;
>>>>>       int got_fds = 0;
>>>>> +    int *tmp_fds;
>>>>>       int ret;
>>>>> +    *fd_num = 0;
>>>>> +
>>>>>       memset(&msgh, 0, sizeof(msgh));
>>>>>       iov.iov_base = buf;
>>>>>       iov.iov_len  = buflen;
>>>>> @@ -131,13 +137,22 @@ read_fd_message(int sockfd, char *buf, int buflen, int *fds, int fd_num)
>>>>>           if ((cmsg->cmsg_level == SOL_SOCKET) &&
>>>>>               (cmsg->cmsg_type == SCM_RIGHTS)) {
>>>>>               got_fds = (cmsg->cmsg_len - CMSG_LEN(0)) / sizeof(int);
>>>>> +            if (got_fds > max_fds) {
>>>>
>>>> Hmm. I just noticed that 'msg_controllen' is set to receive
>>>> not more than max_fds descriptors. So, this case should not
>>>> be possible. We will receive MSG_CTRUNC and return before
>>>> the loop.
>>>
>>> Maybe it is better to remove check for MSG_CTRUNC.
>> s/remove/rework/
>>
>>> IIUC, if MSG_CTRUNC happens, we may have to close anyway the ones
>>> received.
>>>
>>> Do you agree?
> 
> So it seems that other use of MSG_CTRUNC in DPDK and QEMU does care
> to close the ones that would have been received and just return an
> error.

Did you mean 'does not care'?
'read_msg()' in lib/librte_eal/common/eal_common_proc.c just returns -1
and 'slave_read()' in hw/virtio/vhost-user.c does not close fds, because
'fdsize' is not set at the time of checking the flag.

> 
> I propose to do the same for now, an remove the got_fds > max_fds part.
> 
>>>> +                RTE_LOG(ERR, VHOST_CONFIG,
>>>>> +                    "Received msg contains more fds than supported\n");
>>>>> +                tmp_fds = (int *)CMSG_DATA(cmsg);
>>>>> +                while (got_fds--)
>>>>> +                    close(tmp_fds[got_fds]);
>>>>> +                return -1;
>>>>> +            }
>>>>> +            *fd_num = got_fds;
>>>>>               memcpy(fds, CMSG_DATA(cmsg), got_fds * sizeof(int));
>>>>>               break;
>>>>>           }
>>>>>       }
>>>>>       /* Clear out unused file descriptors */
>>>>> -    while (got_fds < fd_num)
>>>>> +    while (got_fds < max_fds)
>>>>>           fds[got_fds++] = -1;
>>>>>       return ret;
>>>>> diff --git a/lib/librte_vhost/vhost_user.c b/lib/librte_vhost/vhost_user.c
>>>>> index 83d3e6321..c1c5f35ff 100644
>>>>> --- a/lib/librte_vhost/vhost_user.c
>>>>> +++ b/lib/librte_vhost/vhost_user.c
>>>>> @@ -1509,7 +1509,7 @@ read_vhost_message(int sockfd, struct VhostUserMsg *msg)
>>>>>       int ret;
>>>>>       ret = read_fd_message(sockfd, (char *)msg, VHOST_USER_HDR_SIZE,
>>>>> -        msg->fds, VHOST_MEMORY_MAX_NREGIONS);
>>>>> +        msg->fds, VHOST_MEMORY_MAX_NREGIONS, &msg->fd_num);
>>>>>       if (ret <= 0)
>>>>>           return ret;
>>>>> diff --git a/lib/librte_vhost/vhost_user.h b/lib/librte_vhost/vhost_user.h
>>>>> index 62654f736..9a91d496b 100644
>>>>> --- a/lib/librte_vhost/vhost_user.h
>>>>> +++ b/lib/librte_vhost/vhost_user.h
>>>>> @@ -132,6 +132,7 @@ typedef struct VhostUserMsg {
>>>>>           VhostUserVringArea area;
>>>>>       } payload;
>>>>>       int fds[VHOST_MEMORY_MAX_NREGIONS];
>>>>> +    int fd_num;
>>>>>   } __attribute((packed)) VhostUserMsg;
>>>>>   #define VHOST_USER_HDR_SIZE offsetof(VhostUserMsg, payload.u64)
>>>>> @@ -155,7 +156,8 @@ int vhost_user_iotlb_miss(struct virtio_net *dev, uint64_t iova, uint8_t perm);
>>>>>   int vhost_user_host_notifier_ctrl(int vid, bool enable);
>>>>>   /* socket.c */
>>>>> -int read_fd_message(int sockfd, char *buf, int buflen, int *fds, int fd_num);
>>>>> +int read_fd_message(int sockfd, char *buf, int buflen, int *fds, int max_fds,
>>>>> +        int *fd_num);
>>>>>   int send_fd_message(int sockfd, char *buf, int buflen, int *fds, int fd_num);
>>>>>   #endif
>>>>>
> 
>