Re: [PATCH linux-next V2] cifs: Make big endian multiplex IDsequences monotonic on the wire

[Jeff Layton]

On Wed, 16 Oct 2013 10:32:42 -0600
Tim Gardner <timg@xxxxxxx> wrote:

> The multiplex identifier (MID) in the SMB header is only
> ever used by the client, in conjunction with PID, to match responses
> from the server. As such, the endianess of the MID is not important.
> However, When tracing packet sequences on the wire, protocol analyzers
> such as wireshark display MID as little endian. It is much more informative
> for the on-the-wire MID sequences to match debug information emitted by the
> CIFS driver.  Therefore, one should write and read MID in the SMB header
> assuming it is always little endian.
> 
> Observed from wireshark during the protocol negotiation
> and session setup:
> 
>         Multiplex ID: 256
>         Multiplex ID: 256
>         Multiplex ID: 512
>         Multiplex ID: 512
>         Multiplex ID: 768
>         Multiplex ID: 768
> 
> After this patch on-the-wire MID values begin at 1 and increase monotonically.
> 
> Introduce get_next_mid64() for the internal consumers that use the full 64 bit
> multiplex identifier.
> 
> Introduce the helpers get_mid() and compare_mid() to make the endian
> translation clear.
> 
> Cc: Jeff Layton <jlayton@xxxxxxxxxx>
> Cc: Steve French <sfrench@xxxxxxxxx>
> Signed-off-by: Tim Gardner <timg@xxxxxxx>
> ---
> 
> V2 - get an endian appropriate copy of 'mid' for debug output in checkSMB().
>      Actually use the new helper get_mid() wherever smb->Mid is referenced.
> 
>  fs/cifs/cifsglob.h      |   25 ++++++++++++++++++++++++-
>  fs/cifs/misc.c          |   10 ++++++----
>  fs/cifs/smb1ops.c       |    4 ++--
>  fs/cifs/smb2transport.c |    2 +-
>  fs/cifs/transport.c     |    2 +-
>  5 files changed, 34 insertions(+), 9 deletions(-)
> 
> diff --git a/fs/cifs/cifsglob.h b/fs/cifs/cifsglob.h
> index 52b6f6c..535e324 100644
> --- a/fs/cifs/cifsglob.h
> +++ b/fs/cifs/cifsglob.h
> @@ -620,11 +620,34 @@ set_credits(struct TCP_Server_Info *server, const int val)
>  }
>  
>  static inline __u64
> -get_next_mid(struct TCP_Server_Info *server)
> +get_next_mid64(struct TCP_Server_Info *server)
>  {
>  	return server->ops->get_next_mid(server);
>  }
>  
> +static inline __u16
> +get_next_mid(struct TCP_Server_Info *server)
> +{
> +	__u16 mid = get_next_mid64(server);
> +	/*
> +	 * The value in the SMB header should be little endian for easy
> +	 * on-the-wire decoding.
> +	 */
> +	return cpu_to_le16(mid);
> +}
> +
> +static inline __u16
> +get_mid(const struct smb_hdr *smb)
> +{
> +	return le16_to_cpu(smb->Mid);
> +}
> +
> +static inline bool
> +compare_mid(__u16 mid, const struct smb_hdr *smb)
> +{
> +	return mid == le16_to_cpu(smb->Mid);
> +}
> +
>  /*
>   * When the server supports very large reads and writes via POSIX extensions,
>   * we can allow up to 2^24-1, minus the size of a READ/WRITE_AND_X header, not
> diff --git a/fs/cifs/misc.c b/fs/cifs/misc.c
> index 298e31e..2f9f379 100644
> --- a/fs/cifs/misc.c
> +++ b/fs/cifs/misc.c
> @@ -295,7 +295,8 @@ check_smb_hdr(struct smb_hdr *smb)
>  	if (smb->Command == SMB_COM_LOCKING_ANDX)
>  		return 0;
>  
> -	cifs_dbg(VFS, "Server sent request, not response. mid=%u\n", smb->Mid);
> +	cifs_dbg(VFS, "Server sent request, not response. mid=%u\n",
> +		 get_mid(smb));
>  	return 1;
>  }
>  
> @@ -351,6 +352,7 @@ checkSMB(char *buf, unsigned int total_read)
>  	}
>  
>  	if (4 + rfclen != clc_len) {
> +		__u16 mid = get_mid(smb);
>  		/* check if bcc wrapped around for large read responses */
>  		if ((rfclen > 64 * 1024) && (rfclen > clc_len)) {
>  			/* check if lengths match mod 64K */
> @@ -358,11 +360,11 @@ checkSMB(char *buf, unsigned int total_read)
>  				return 0; /* bcc wrapped */
>  		}
>  		cifs_dbg(FYI, "Calculated size %u vs length %u mismatch for mid=%u\n",
> -			 clc_len, 4 + rfclen, smb->Mid);
> +			 clc_len, 4 + rfclen, mid);
>  
>  		if (4 + rfclen < clc_len) {
>  			cifs_dbg(VFS, "RFC1001 size %u smaller than SMB for mid=%u\n",
> -				 rfclen, smb->Mid);
> +				 rfclen, mid);
>  			return -EIO;
>  		} else if (rfclen > clc_len + 512) {
>  			/*
> @@ -375,7 +377,7 @@ checkSMB(char *buf, unsigned int total_read)
>  			 * data to 512 bytes.
>  			 */
>  			cifs_dbg(VFS, "RFC1001 size %u more than 512 bytes larger than SMB for mid=%u\n",
> -				 rfclen, smb->Mid);
> +				 rfclen, mid);
>  			return -EIO;
>  		}
>  	}
> diff --git a/fs/cifs/smb1ops.c b/fs/cifs/smb1ops.c
> index 8233b17..09ef8f3 100644
> --- a/fs/cifs/smb1ops.c
> +++ b/fs/cifs/smb1ops.c
> @@ -67,7 +67,7 @@ send_nt_cancel(struct TCP_Server_Info *server, void *buf,
>  	mutex_unlock(&server->srv_mutex);
>  
>  	cifs_dbg(FYI, "issued NT_CANCEL for mid %u, rc = %d\n",
> -		 in_buf->Mid, rc);
> +		 get_mid(in_buf), rc);
>  
>  	return rc;
>  }
> @@ -101,7 +101,7 @@ cifs_find_mid(struct TCP_Server_Info *server, char *buffer)
>  
>  	spin_lock(&GlobalMid_Lock);
>  	list_for_each_entry(mid, &server->pending_mid_q, qhead) {
> -		if (mid->mid == buf->Mid &&
> +		if (compare_mid(mid->mid, buf) &&
>  		    mid->mid_state == MID_REQUEST_SUBMITTED &&
>  		    le16_to_cpu(mid->command) == buf->Command) {
>  			spin_unlock(&GlobalMid_Lock);
> diff --git a/fs/cifs/smb2transport.c b/fs/cifs/smb2transport.c
> index 340abca..c523617 100644
> --- a/fs/cifs/smb2transport.c
> +++ b/fs/cifs/smb2transport.c
> @@ -466,7 +466,7 @@ smb2_verify_signature(struct smb_rqst *rqst, struct TCP_Server_Info *server)
>  static inline void
>  smb2_seq_num_into_buf(struct TCP_Server_Info *server, struct smb2_hdr *hdr)
>  {
> -	hdr->MessageId = get_next_mid(server);
> +	hdr->MessageId = get_next_mid64(server);
>  }
>  
>  static struct mid_q_entry *
> diff --git a/fs/cifs/transport.c b/fs/cifs/transport.c
> index 6fdcb1b..057b2c0 100644
> --- a/fs/cifs/transport.c
> +++ b/fs/cifs/transport.c
> @@ -58,7 +58,7 @@ AllocMidQEntry(const struct smb_hdr *smb_buffer, struct TCP_Server_Info *server)
>  		return temp;
>  	else {
>  		memset(temp, 0, sizeof(struct mid_q_entry));
> -		temp->mid = smb_buffer->Mid;	/* always LE */
> +		temp->mid = get_mid(smb_buffer);
>  		temp->pid = current->pid;
>  		temp->command = cpu_to_le16(smb_buffer->Command);
>  		cifs_dbg(FYI, "For smb_command %d\n", smb_buffer->Command);

Looks good...

Reviewed-by: Jeff Layton <jlayton@xxxxxxxxxx>
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