Signal Handler Use of a Non-reentrant Function
The product defines a signal handler that calls a non-reentrant function.
Description
Non-reentrant functions are functions that cannot safely be called, interrupted, and then recalled before the first call has finished without resulting in memory corruption. This can lead to an unexpected system state and unpredictable results with a variety of potential consequences depending on context, including denial of service and code execution.
Many functions are not reentrant, but some of them can result in the corruption of memory if they are used in a signal handler. The function call syslog() is an example of this. In order to perform its functionality, it allocates a small amount of memory as "scratch space." If syslog() is suspended by a signal call and the signal handler calls syslog(), the memory used by both of these functions enters an undefined, and possibly, exploitable state. Implementations of malloc() and free() manage metadata in global structures in order to track which memory is allocated versus which memory is available, but they are non-reentrant. Simultaneous calls to these functions can cause corruption of the metadata.
Demonstrations
The following examples help to illustrate the nature of this weakness and describe methods or techniques which can be used to mitigate the risk.
Note that the examples here are by no means exhaustive and any given weakness may have many subtle varieties, each of which may require different detection methods or runtime controls.
Example One
In this example, a signal handler uses syslog() to log a message:
char *message;
void sh(int dummy) {
syslog(LOG_NOTICE,"%s\n",message);
sleep(10);
exit(0);
}
int main(int argc,char* argv[]) {
...
signal(SIGHUP,sh);
signal(SIGTERM,sh);
sleep(10);
exit(0);
}
If the execution of the first call to the signal handler is suspended after invoking syslog(), and the signal handler is called a second time, the memory allocated by syslog() enters an undefined, and possibly, exploitable state.See Also
Weaknesses in this category are related to concurrency.
Weaknesses in this category are related to the rules and recommendations in the Signals (SIG) section of the SEI CERT C Coding Standard.
This category identifies Software Fault Patterns (SFPs) within the Use of an Improper API cluster (SFP3).
This view (slice) covers all the elements in CWE.
This view (slice) lists weaknesses that can be introduced during implementation.
This view (slice) covers issues that are found in C++ programs that are not common to all languages.
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