Signal Handler Use of a Non-reentrant Function

The program 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

SEI CERT C Coding Standard - Guidelines 11. Signals (SIG)

Weaknesses in this category are related to the rules and recommendations in the Signals (SIG) section of the SEI CERT C Coding Standard.

SFP Secondary Cluster: Use of an Improper API

This category identifies Software Fault Patterns (SFPs) within the Use of an Improper API cluster (SFP3).

CERT C++ Secure Coding Section 11 - Signals (SIG)

Weaknesses in this category are related to rules in the Signals (SIG) section of the CERT C++ Secure Coding Standard. Since not all rules map to specific weaknesses, t...

Comprehensive CWE Dictionary

This view (slice) covers all the elements in CWE.

Weaknesses Introduced During Implementation

This view (slice) lists weaknesses that can be introduced during implementation.

Weaknesses Introduced During Design

This view (slice) lists weaknesses that can be introduced during design.


Common Weakness Enumeration content on this website is copyright of The MITRE Corporation unless otherwise specified. Use of the Common Weakness Enumeration and the associated references on this website are subject to the Terms of Use as specified by The MITRE Corporation.