[CIFS] Workaround incomplete byte length returned by some servers on small SMB responses

Signed-off-by: Steve French <[e-mail]>

fs/cifs/cifsproto.h

···
 				struct smb_hdr * /* input */ ,
 				struct smb_hdr * /* out */ ,
 				int * /* bytes returned */);
-extern int checkSMB(struct smb_hdr *smb, __u16 mid, int length);
+extern int checkSMB(struct smb_hdr *smb, __u16 mid, unsigned int length);
 extern int is_valid_oplock_break(struct smb_hdr *smb, struct TCP_Server_Info *);
 extern int is_size_safe_to_change(struct cifsInodeInfo *);
 extern struct cifsFileInfo *find_writable_file(struct cifsInodeInfo *);

fs/cifs/misc.c

···
 }
 
 int
-checkSMB(struct smb_hdr *smb, __u16 mid, int length)
+checkSMB(struct smb_hdr *smb, __u16 mid, unsigned int length)
 {
 	__u32 len = smb->smb_buf_length;
 	__u32 clc_len;  /* calculated length */
 	cFYI(0, ("checkSMB Length: 0x%x, smb_buf_length: 0x%x", length, len));
-	if (((unsigned int)length < 2 + sizeof (struct smb_hdr)) ||
-	    (len > CIFSMaxBufSize + MAX_CIFS_HDR_SIZE - 4)) {
-		if ((unsigned int)length < 2 + sizeof (struct smb_hdr)) {
-			if (((unsigned int)length >= 
-				sizeof (struct smb_hdr) - 1)
+
+	if (length < 2 + sizeof (struct smb_hdr)) {
+		if ((length >= sizeof (struct smb_hdr) - 1)
 			    && (smb->Status.CifsError != 0)) {
-				smb->WordCount = 0;
-				/* some error cases do not return wct and bcc */
+			smb->WordCount = 0;
+			/* some error cases do not return wct and bcc */
+			return 0;
+		} else if ((length == sizeof(struct smb_hdr) + 1) && 
+				(smb->WordCount == 0)) {
+			char * tmp = (char *)smb;
+			/* Need to work around a bug in two servers here */
+			/* First, check if the part of bcc they sent was zero */
+			if (tmp[sizeof(struct smb_hdr)] == 0) {
+				/* some servers return only half of bcc
+				 * on simple responses (wct, bcc both zero)
+				 * in particular have seen this on
+				 * ulogoffX and FindClose. This leaves
+				 * one byte of bcc potentially unitialized
+				 */
+				/* zero rest of bcc */
+				tmp[sizeof(struct smb_hdr)+1] = 0;
 				return 0;
-			} else {
-				cERROR(1, ("Length less than smb header size"));
 			}
+			cERROR(1,("rcvd invalid byte count (bcc)"));
+		} else {
+			cERROR(1, ("Length less than smb header size"));
 		}
-		if (len > CIFSMaxBufSize + MAX_CIFS_HDR_SIZE - 4)
-			cERROR(1, ("smb length greater than MaxBufSize, mid=%d",
+		return 1;
+	}
+	if (len > CIFSMaxBufSize + MAX_CIFS_HDR_SIZE - 4) {
+		cERROR(1, ("smb length greater than MaxBufSize, mid=%d",
 				   smb->Mid));
 		return 1;
 	}
···
 		return 1;
 	clc_len = smbCalcSize_LE(smb);
 
-	if(4 + len != (unsigned int)length) {
+	if(4 + len != length) {
 		cERROR(1, ("Length read does not match RFC1001 length %d",len));
 		return 1;
 	}