cifs: fix parsing of symbolic link error response

RHBZ: 1672539

In smb2_query_symlink(), if we are parsing the error buffer but it is not something
we recognize as a symlink we should return -EINVAL and not -ENOENT.
I.e. the entry does exist, it is just not something we recognize.

Additionally, add check to verify that that the errortag and the reparsetag all make sense.

Signed-off-by: Ronnie Sahlberg <lsahlber@redhat.com>
Acked-by: Paulo Alcantara <palcantara@suse.de>
Signed-off-by: Steve French <stfrench@microsoft.com>

fs/cifs/smb2ops.c

@@ -2605,26 +2605,32 @@ smb2_query_symlink(const unsigned int xid, struct cifs_tcon *tcon,
 	err_buf = err_iov.iov_base;
 	if (le32_to_cpu(err_buf->ByteCount) < sizeof(struct smb2_symlink_err_rsp) ||
 	    err_iov.iov_len < SMB2_SYMLINK_STRUCT_SIZE) {
-		rc = -ENOENT;
+		rc = -EINVAL;
+		goto querty_exit;
+	}
+
+	symlink = (struct smb2_symlink_err_rsp *)err_buf->ErrorData;
+	if (le32_to_cpu(symlink->SymLinkErrorTag) != SYMLINK_ERROR_TAG ||
+	    le32_to_cpu(symlink->ReparseTag) != IO_REPARSE_TAG_SYMLINK) {
+		rc = -EINVAL;
 		goto querty_exit;
 	}
 
 	/* open must fail on symlink - reset rc */
 	rc = 0;
-	symlink = (struct smb2_symlink_err_rsp *)err_buf->ErrorData;
 	sub_len = le16_to_cpu(symlink->SubstituteNameLength);
 	sub_offset = le16_to_cpu(symlink->SubstituteNameOffset);
 	print_len = le16_to_cpu(symlink->PrintNameLength);
 	print_offset = le16_to_cpu(symlink->PrintNameOffset);
 
 	if (err_iov.iov_len < SMB2_SYMLINK_STRUCT_SIZE + sub_offset + sub_len) {
-		rc = -ENOENT;
+		rc = -EINVAL;
 		goto querty_exit;
 	}
 
 	if (err_iov.iov_len <
 	    SMB2_SYMLINK_STRUCT_SIZE + print_offset + print_len) {
-		rc = -ENOENT;
+		rc = -EINVAL;
 		goto querty_exit;
 	}
 

fs/cifs/smb2pdu.h

@@ -166,6 +166,8 @@ struct smb2_err_rsp {
 	__u8   ErrorData[1];  /* variable length */
 } __packed;
 
+#define SYMLINK_ERROR_TAG 0x4c4d5953
+
 struct smb2_symlink_err_rsp {
 	__le32 SymLinkLength;
 	__le32 SymLinkErrorTag;