CIFS: Fix too big maxBuf size for SMB3 mounts

SMB3 servers can respond with MaxTransactSize of more than 4M
that can cause a memory allocation error returned from kmalloc
in a lock codepath. Also the client doesn't support multicredit
requests now and allows buffer sizes of 65536 bytes only. Set
MaxTransactSize to this maximum supported value.

Cc: stable@vger.kernel.org # 3.7+
Signed-off-by: Pavel Shilovsky <piastry@etersoft.ru>
Acked-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Steve French <smfrench@gmail.com>
diff --git a/fs/cifs/smb2glob.h b/fs/cifs/smb2glob.h
index c383508..bc0bb9c 100644
--- a/fs/cifs/smb2glob.h
+++ b/fs/cifs/smb2glob.h
@@ -57,4 +57,7 @@
 #define SMB2_CMACAES_SIZE (16)
 #define SMB3_SIGNKEY_SIZE (16)
 
+/* Maximum buffer size value we can send with 1 credit */
+#define SMB2_MAX_BUFFER_SIZE 65536
+
 #endif	/* _SMB2_GLOB_H */