cifs: handle large EA requests more gracefully in smb2+

Update reading the EA using increasingly larger buffer sizes
until the response will fit in the buffer, or we exceed the
(arbitrary) maximum set to 64kb.

Without this change, a user is able to add more and more EAs using
setfattr until the point where the total space of all EAs exceed 2kb
at which point the user can no longer list the EAs at all
and getfattr will abort with an error.

The same issue still exists for EAs in SMB1.

Signed-off-by: Ronnie Sahlberg <[e-mail]>
Reported-by: Xiaoli Feng <[e-mail]>
Signed-off-by: Steve French <[e-mail]>

fs/cifs/smb2maperror.c

···
 	{STATUS_DATATYPE_MISALIGNMENT, -EIO, "STATUS_DATATYPE_MISALIGNMENT"},
 	{STATUS_BREAKPOINT, -EIO, "STATUS_BREAKPOINT"},
 	{STATUS_SINGLE_STEP, -EIO, "STATUS_SINGLE_STEP"},
-	{STATUS_BUFFER_OVERFLOW, -EIO, "STATUS_BUFFER_OVERFLOW"},
+	{STATUS_BUFFER_OVERFLOW, -E2BIG, "STATUS_BUFFER_OVERFLOW"},
 	{STATUS_NO_MORE_FILES, -ENODATA, "STATUS_NO_MORE_FILES"},
 	{STATUS_WAKE_SYSTEM_DEBUGGER, -EIO, "STATUS_WAKE_SYSTEM_DEBUGGER"},
 	{STATUS_HANDLES_CLOSED, -EIO, "STATUS_HANDLES_CLOSED"},

fs/cifs/smb2ops.c

···
 	struct cifs_open_parms oparms;
 	struct cifs_fid fid;
 	struct smb2_file_full_ea_info *smb2_data;
+	int ea_buf_size = SMB2_MIN_EA_BUF;
 
 	utf16_path = cifs_convert_path_to_utf16(path, cifs_sb);
 	if (!utf16_path)
···
 		return rc;
 	}
 
-	smb2_data = kzalloc(SMB2_MAX_EA_BUF, GFP_KERNEL);
-	if (smb2_data == NULL) {
-		SMB2_close(xid, tcon, fid.persistent_fid, fid.volatile_fid);
-		return -ENOMEM;
+	while (1) {
+		smb2_data = kzalloc(ea_buf_size, GFP_KERNEL);
+		if (smb2_data == NULL) {
+			SMB2_close(xid, tcon, fid.persistent_fid,
+				   fid.volatile_fid);
+			return -ENOMEM;
+		}
+
+		rc = SMB2_query_eas(xid, tcon, fid.persistent_fid,
+				    fid.volatile_fid,
+				    ea_buf_size, smb2_data);
+
+		if (rc != -E2BIG)
+			break;
+
+		kfree(smb2_data);
+		ea_buf_size <<= 1;
+
+		if (ea_buf_size > SMB2_MAX_EA_BUF) {
+			cifs_dbg(VFS, "EA size is too large\n");
+			SMB2_close(xid, tcon, fid.persistent_fid,
+				   fid.volatile_fid);
+			return -ENOMEM;
+		}
 	}
 
-	rc = SMB2_query_eas(xid, tcon, fid.persistent_fid, fid.volatile_fid,
-			    smb2_data);
 	SMB2_close(xid, tcon, fid.persistent_fid, fid.volatile_fid);
 
 	if (!rc)

fs/cifs/smb2pdu.c

···
 }
 
 int SMB2_query_eas(const unsigned int xid, struct cifs_tcon *tcon,
-	u64 persistent_fid, u64 volatile_fid,
-	struct smb2_file_full_ea_info *data)
+		   u64 persistent_fid, u64 volatile_fid,
+		   int ea_buf_size, struct smb2_file_full_ea_info *data)
 {
 	return query_info(xid, tcon, persistent_fid, volatile_fid,
 			  FILE_FULL_EA_INFORMATION, SMB2_O_INFO_FILE, 0,
-			  SMB2_MAX_EA_BUF,
+			  ea_buf_size,
 			  sizeof(struct smb2_file_full_ea_info),
 			  (void **)&data,
 			  NULL);

fs/cifs/smb2pdu.h

···
 	char   FileName[0];     /* Name to be assigned to new link */
 } __packed; /* level 11 Set */
 
-#define SMB2_MAX_EA_BUF 2048
+#define SMB2_MIN_EA_BUF  2048
+#define SMB2_MAX_EA_BUF 65536
 
 struct smb2_file_full_ea_info { /* encoding of response for level 15 */
 	__le32 next_entry_offset;

fs/cifs/smb2proto.h

···
 		      u64 persistent_file_id, u64 volatile_file_id);
 extern int SMB2_query_eas(const unsigned int xid, struct cifs_tcon *tcon,
 			  u64 persistent_file_id, u64 volatile_file_id,
+			  int ea_buf_size,
 			  struct smb2_file_full_ea_info *data);
 extern int SMB2_query_info(const unsigned int xid, struct cifs_tcon *tcon,
 			   u64 persistent_file_id, u64 volatile_file_id,