The program resizes a block of allocated memory. If the resize fails, the original block will be leaked.
Memory leaks have two common and sometimes overlapping causes:
- Error conditions and other exceptional circumstances.
- Confusion over which part of the program is responsible for freeing the memory.
Most memory leaks result in general software reliability problems, but if an attacker can intentionally trigger a memory leak, the attacker might be able to launch a denial of service attack (by crashing the program) or take advantage of other unexpected program behavior resulting from a low memory condition [1].
Example 1: The following C function leaks a block of allocated memory if the call to realloc()
fails to resize the original allocation.
char* getBlocks(int fd) {
int amt;
int request = BLOCK_SIZE;
char* buf = (char*) malloc(BLOCK_SIZE + 1);
if (!buf) {
goto ERR;
}
amt = read(fd, buf, request);
while ((amt % BLOCK_SIZE) != 0) {
if (amt < request) {
goto ERR;
}
request = request + BLOCK_SIZE;
buf = realloc(buf, request);
if (!buf) {
goto ERR;
}
amt = read(fd, buf, request);
}
return buf;
ERR:
if (buf) {
free(buf);
}
return NULL;
}
[1] Standards Mapping - OWASP Top 10 2004 - (OWASP 2004) A9 Application Denial of Service
[2] Standards Mapping - Security Technical Implementation Guide Version 3 - (STIG 3) APP6080 CAT II
[3] Standards Mapping - Common Weakness Enumeration - (CWE) CWE ID 401
[4] Standards Mapping - Payment Card Industry Data Security Standard Version 1.1 - (PCI 1.1) Requirement 6.5.9