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qjson: Limit number of tokens in addition to total size

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Commit 29c75dd "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: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Message-Id: <1448486613-17634-13-git-send-email-armbru@redhat.com>
This commit is contained in:
Markus Armbruster 2015-11-25 22:23:33 +01:00
parent 9bada89711
commit df649835fe
1 changed files with 2 additions and 0 deletions
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2
qobject/json-streamer.c
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@ -16,6 +16,7 @@
#include "qapi/qmp/json-streamer.h" #include "qapi/qmp/json-streamer.h"
#define MAX_TOKEN_SIZE (64ULL << 20) #define MAX_TOKEN_SIZE (64ULL << 20)
#define MAX_TOKEN_COUNT (2ULL << 20)
#define MAX_NESTING (1ULL << 10) #define MAX_NESTING (1ULL << 10)
static void json_message_free_tokens(JSONMessageParser *parser) 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)) { parser->bracket_count == 0)) {
goto out_emit; goto out_emit;
} else if (parser->token_size > MAX_TOKEN_SIZE || } 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) { parser->bracket_count + parser->brace_count > MAX_NESTING) {
/* Security consideration, we limit total memory allocated per object /* Security consideration, we limit total memory allocated per object
* and the maximum recursion depth that a message can force. * and the maximum recursion depth that a message can force.