cifs: Make big endian multiplex ID sequences monotonic on the wire

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.

Reviewed-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Tim Gardner <timg@tpi.com>
Signed-off-by: Steve French <smfrench@gmail.com>

1 files changed, 6 insertions, 4 deletions

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;
 		}
 	}