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char string[]*path = "Hello secure coding wiki!";getenv("PATH"); /* PATH is something like "/usr/bin:/bin:/usr/sbin:/sbin" */ char *token; token = strtok(stringpath, ' '":"); puts(token); while (token = strtok(NULL0, ' '":")) { puts(token); } printf("PATH: %s\n", path); /* stringPATH is hasnow been modifiedjust "/usr/bin" */ |
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In this example, the {{strtok()}} function is used to parse the first argument into spacecolon-delimited tokens; it will output each word from the string on a new line. However, after the while loop ends, stringpath\[\] will have been modified to look like this: {{"Hello\0secure\0coding\0wiki/usr/bin\0/bin\0/usr/sbin\0/sbin\0"}}. This is an issue on several levels. If Anywe furthercheck manipulationour oflocal {{stringpath}} operating on the assumption that it is still whole will see only "Hello" instead of the expected string valuevariable, we will only see {{/usr/bin}} now. Even worse, we have changed the environment variable PATH, which could cause more confusion (see ENV30-C). |
Compliant Solutions
One possible solution is to copy the string being tokenized into a temporary buffer which isn't referenced after the calls to strtok():
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