State synchronization refers to a set of flaws involving
contradictory states of execution in a process which result in undefined
behavior.
Time of Introduction
Architecture and Design
Implementation
Applicable Platforms
Languages
All
Common Consequences
Scope
Effect
Depending on the nature of the state of corruption, any of the listed
consequences may result.
Likelihood of Exploit
Medium to High
Demonstrative Examples
Example 1
(Bad Code)
C and C++
static void print(char * string) {
char * word;
int counter;
fflush(stdout);
for(word = string; counter = *word++; )
putc(counter, stdout);
}
int main(void) {
pid_t pid;
if( (pid = fork()) < 0)
exit(-2);
else if( pid == 0)
print("child");
else print("parent\n");
exit(0);
}
(Bad Code)
Java
class read{
private int lcount;
private int rcount;
private int wcount;
public void getRead(){
while ((lcount == -1) || (wcount !=0));
lcount++;
}
public void getWrite(){
while ((lcount == -0);
lcount--;
lcount=-1;
}
public void killLocks(){
if (lcount==0)
return;
else if (lcount == -1)
lcount++;
else lcount--;
}
}
Potential Mitigations
Phase
Description
Implementation
Pay attention to asynchronous actions in processes and make copious
use of sanity checks in systems that may be subject to synchronization
errors.
Other Notes
The class of synchronization errors is large and varied, but all rely on
the same essential flaw. The state of the system is not what the process
expects it to be at a given time. Obviously, the range of possible symptoms
is enormous, as is the range of possible solutions. The flaws presented in
this section are some of the most difficult to diagnose and fix. It is more
important to know how to characterize specific flaws than to gain
information about them.
Description
