cifs: limit amount of data we request for xattrs to CIFSMaxBufSize

minus the various headers and blobs that will be part of the reply.

or else we might trigger a session reconnect.
Signed-off-by: Ronnie Sahlberg <lsahlber@redhat.com>
Signed-off-by: Steve French <stfrench@microsoft.com>
Reviewed-by: Pavel Shilovsky <pshilov@microsoft.com>

fs/cifs/smb2ops.c

@@ -866,7 +866,9 @@ smb2_query_eas(const unsigned int xid, struct cifs_tcon *tcon,
 				      FILE_READ_EA,
 				      FILE_FULL_EA_INFORMATION,
 				      SMB2_O_INFO_FILE,
-				      SMB2_MAX_EA_BUF,
+				      CIFSMaxBufSize -
+				      MAX_SMB2_CREATE_RESPONSE_SIZE -
+				      MAX_SMB2_CLOSE_RESPONSE_SIZE,
 				      &rsp_iov, &buftype, cifs_sb);
 	if (rc) {
 		/*

fs/cifs/smb2pdu.h

@@ -85,6 +85,7 @@
 #define NUMBER_OF_SMB2_COMMANDS	0x0013
 
 /* 52 transform hdr + 64 hdr + 88 create rsp */
+#define SMB2_TRANSFORM_HEADER_SIZE 52
 #define MAX_SMB2_HDR_SIZE 204
 
 #define SMB2_PROTO_NUMBER cpu_to_le32(0x424d53fe)
@@ -648,6 +649,13 @@ struct smb2_create_req {
 	__u8   Buffer[0];
 } __packed;
 
+/*
+ * Maximum size of a SMB2_CREATE response is 64 (smb2 header) +
+ * 88 (fixed part of create response) + 520 (path) + 150 (contexts) +
+ * 2 bytes of padding.
+ */
+#define MAX_SMB2_CREATE_RESPONSE_SIZE 824
+
 struct smb2_create_rsp {
 	struct smb2_sync_hdr sync_hdr;
 	__le16 StructureSize;	/* Must be 89 */
@@ -996,6 +1004,11 @@ struct smb2_close_req {
 	__u64  VolatileFileId; /* opaque endianness */
 } __packed;
 
+/*
+ * Maximum size of a SMB2_CLOSE response is 64 (smb2 header) + 60 (data)
+ */
+#define MAX_SMB2_CLOSE_RESPONSE_SIZE 124
+
 struct smb2_close_rsp {
 	struct smb2_sync_hdr sync_hdr;
 	__le16 StructureSize; /* 60 */
@@ -1398,8 +1411,6 @@ struct smb2_file_link_info { /* encoding of request for level 11 */
 	char   FileName[0];     /* Name to be assigned to new link */
 } __packed; /* level 11 Set */
 
-#define SMB2_MAX_EA_BUF 65536
-
 struct smb2_file_full_ea_info { /* encoding of response for level 15 */
 	__le32 next_entry_offset;
 	__u8   flags;