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

From: Long Li
Date: Wed Mar 25 2020 - 22:43:34 EST

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

Agreed. Using a magic number is not a good idea.

I was looking at request size definitions in
"fs/cifs/smb2pdu.c", they are defined at
static const int smb2_req_struct_sizes[NUMBER_OF_SMB2_COMMANDS]

for read and write, the sizes are:
/* SMB2_READ */ 49,
/* SMB2_WRITE */ 49,

They are used to calculate command header sizes, and fill in the request headers. Maybe I should use this variable to get the size?

>
>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
>>
>>