Commit df649835 authored by Markus Armbruster's avatar Markus Armbruster
Browse files

qjson: Limit number of tokens in addition to total size 



Commit 29c75ddd "json-streamer: limit the maximum recursion depth and
maximum token count" attempts to guard against excessive heap usage by
limiting total token size (it says "token count", but that's a lie).

Total token size is a rather imprecise predictor of heap usage: many
small tokens use more space than few large tokens with the same input
size, because there's a constant per-token overhead: 37 bytes on my
system.

Tighten this up: limit the token count to 2Mi.  Chosen to roughly
match the 64MiB total token size limit.

Signed-off-by: default avatarMarkus Armbruster <armbru@redhat.com>
Reviewed-by: default avatarEric Blake <eblake@redhat.com>
Message-Id: <1448486613-17634-13-git-send-email-armbru@redhat.com>
parent 9bada897

qobject/json-streamer.c

+2 −0
Original line number Diff line number Diff line
@@ -16,6 +16,7 @@ 
#include "qapi/qmp/json-streamer.h"



#define MAX_TOKEN_SIZE (64ULL << 20)

#define MAX_TOKEN_COUNT (2ULL << 20)

#define MAX_NESTING (1ULL << 10)



static void json_message_free_tokens(JSONMessageParser *parser)
@@ -68,6 +69,7 @@ static void json_message_process_token(JSONLexer *lexer, GString *input, 
         parser->bracket_count == 0)) {

        goto out_emit;

    } else if (parser->token_size > MAX_TOKEN_SIZE ||

               g_queue_get_length(parser->tokens) > MAX_TOKEN_COUNT ||

               parser->bracket_count + parser->brace_count > MAX_NESTING) {

        /* Security consideration, we limit total memory allocated per object

         * and the maximum recursion depth that a message can force.