Re: [PATCH] cifs: smbd: Calculate the correct maximum packet size for segmented SMBDirect send/receive

[ronnie sahlberg]

Long Li,

Mostly looks good  but the magic constant 49 I think is wrong.
49 is the structure size of the read/write request header
but for these sizes, if they are odd it just means that the header contain a
variable sized blob.
I.e. the size is 48 bytes (for the fixed part of the header) + a variable part
which in this case are the ChannelInfo blobs.

So we should probably add to smb2pdu.h a
#define MAX_SMB2_READWRITE_RESPONSE_SIZE 48
and use this in the calculations. Then we need to add the maximum size
we will use for ChannelInfo.

Maybe we should have a define also for the MAX_SMB2_CHANNEL_INFO_SIZE

regards
ronnie sahlberg

On Thu, Mar 26, 2020 at 5:31 AM longli--- via samba-technical
<samba-technical@xxxxxxxxxxxxxxx> wrote:
>
> From: Long Li <longli@xxxxxxxxxxxxx>
>
> The packet size needs to take account of SMB2 header size and possible
> encryption header size. This is only done when signing is used and it is for
> RDMA send/receive, not read/write.
>
> Also remove the dead SMBD code in smb2_negotiate_r(w)size.
>
> Signed-off-by: Long Li <longli@xxxxxxxxxxxxx>
> ---
>  fs/cifs/smb2ops.c   | 38 ++++++++++++++++----------------------
>  fs/cifs/smbdirect.c |  3 +--
>  2 files changed, 17 insertions(+), 24 deletions(-)
>
> diff --git a/fs/cifs/smb2ops.c b/fs/cifs/smb2ops.c
> index 4c0922596467..9043d34eef43 100644
> --- a/fs/cifs/smb2ops.c
> +++ b/fs/cifs/smb2ops.c
> @@ -332,16 +332,6 @@ smb2_negotiate_wsize(struct cifs_tcon *tcon, struct smb_vol *volume_info)
>         /* start with specified wsize, or default */
>         wsize = volume_info->wsize ? volume_info->wsize : CIFS_DEFAULT_IOSIZE;
>         wsize = min_t(unsigned int, wsize, server->max_write);
> -#ifdef CONFIG_CIFS_SMB_DIRECT
> -       if (server->rdma) {
> -               if (server->sign)
> -                       wsize = min_t(unsigned int,
> -                               wsize, server->smbd_conn->max_fragmented_send_size);
> -               else
> -                       wsize = min_t(unsigned int,
> -                               wsize, server->smbd_conn->max_readwrite_size);
> -       }
> -#endif
>         if (!(server->capabilities & SMB2_GLOBAL_CAP_LARGE_MTU))
>                 wsize = min_t(unsigned int, wsize, SMB2_MAX_BUFFER_SIZE);
>
> @@ -360,8 +350,15 @@ smb3_negotiate_wsize(struct cifs_tcon *tcon, struct smb_vol *volume_info)
>  #ifdef CONFIG_CIFS_SMB_DIRECT
>         if (server->rdma) {
>                 if (server->sign)
> +                       /*
> +                        * Account for SMB2 data transfer packet header
> +                        * SMB2_READ/SMB2_WRITE (49) and possible encryption
> +                        * headers
> +                        */
>                         wsize = min_t(unsigned int,
> -                               wsize, server->smbd_conn->max_fragmented_send_size);
> +                               wsize,
> +                               server->smbd_conn->max_fragmented_send_size -
> +                                       49 - sizeof(struct smb2_transform_hdr));
>                 else
>                         wsize = min_t(unsigned int,
>                                 wsize, server->smbd_conn->max_readwrite_size);
> @@ -382,16 +379,6 @@ smb2_negotiate_rsize(struct cifs_tcon *tcon, struct smb_vol *volume_info)
>         /* start with specified rsize, or default */
>         rsize = volume_info->rsize ? volume_info->rsize : CIFS_DEFAULT_IOSIZE;
>         rsize = min_t(unsigned int, rsize, server->max_read);
> -#ifdef CONFIG_CIFS_SMB_DIRECT
> -       if (server->rdma) {
> -               if (server->sign)
> -                       rsize = min_t(unsigned int,
> -                               rsize, server->smbd_conn->max_fragmented_recv_size);
> -               else
> -                       rsize = min_t(unsigned int,
> -                               rsize, server->smbd_conn->max_readwrite_size);
> -       }
> -#endif
>
>         if (!(server->capabilities & SMB2_GLOBAL_CAP_LARGE_MTU))
>                 rsize = min_t(unsigned int, rsize, SMB2_MAX_BUFFER_SIZE);
> @@ -411,8 +398,15 @@ smb3_negotiate_rsize(struct cifs_tcon *tcon, struct smb_vol *volume_info)
>  #ifdef CONFIG_CIFS_SMB_DIRECT
>         if (server->rdma) {
>                 if (server->sign)
> +                       /*
> +                        * Account for SMB2 data transfer packet header
> +                        * SMB2_READ/SMB2_WRITE (49) and possible encryption
> +                        * headers
> +                        */
>                         rsize = min_t(unsigned int,
> -                               rsize, server->smbd_conn->max_fragmented_recv_size);
> +                               rsize,
> +                               server->smbd_conn->max_fragmented_recv_size -
> +                                       49 - sizeof(struct smb2_transform_hdr));
>                 else
>                         rsize = min_t(unsigned int,
>                                 rsize, server->smbd_conn->max_readwrite_size);
> diff --git a/fs/cifs/smbdirect.c b/fs/cifs/smbdirect.c
> index eb1e40af9f3a..0327b575ab87 100644
> --- a/fs/cifs/smbdirect.c
> +++ b/fs/cifs/smbdirect.c
> @@ -2097,8 +2097,7 @@ int smbd_send(struct TCP_Server_Info *server,
>         for (i = 0; i < num_rqst; i++)
>                 remaining_data_length += smb_rqst_len(server, &rqst_array[i]);
>
> -       if (remaining_data_length + sizeof(struct smbd_data_transfer) >
> -               info->max_fragmented_send_size) {
> +       if (remaining_data_length > info->max_fragmented_send_size) {
>                 log_write(ERR, "payload size %d > max size %d\n",
>                         remaining_data_length, info->max_fragmented_send_size);
>                 rc = -EINVAL;
> --
> 2.17.1
>
>