The accidental addition of a data-structure sentinel can cause serious programming logic problems.
Data-structure sentinels are often used to mark the structure of data. A common example of this is the null character at the end of strings or a special sentinel to mark the end of a linked list. It is dangerous to allow this type of control data to be easily accessible. Therefore, it is important to protect from the addition or modification of sentinels.
Threat Mapped score: 0.0
Industry: Finiancial
Threat priority: Unclassified
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| Phase | Note |
|---|---|
| Implementation | N/A |
Intro: The following example assigns some character values to a list of characters and prints them each individually, and then as a string. The third character value is intended to be an integer taken from user input and converted to an int.
Body: The first print statement will print each character separated by a space. However, if a NULL byte is read from stdin by fgetc, then it will return 0. When foo is printed as a string, the 0 at character foo[2] will act as a NULL terminator and foo[3] will never be printed.
char *foo; foo=malloc(sizeof(char)*5); foo[0]='a'; foo[1]='a'; foo[2]=fgetc(stdin); foo[3]='c'; foo[4]='\0'; printf("%c %c %c %c %c \n",foo[0],foo[1],foo[2],foo[3],foo[4]); printf("%s\n",foo);