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In most cases, compilers warn about uninitialized variables. These warnings should be resolved as recommended by MSC00-CPP. Compile cleanly at high warning levels.
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Noncompliant Code Example
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In this noncompliant code example, the programmer mistakenly fails to set the local variable {{error_log}} to the {{msg}} argument in the {{report_error()}} function \[ [mercy 06|AA. Bibliography#mercy 06]\]. Because {{error_log}} has not been initialized, on architectures making use of a program stack, it assumes the value already on the stack at this location, which is a pointer to the stack memory allocated to the {{password}} array. The {{sprintf()}} call copies data in {{password}} until a null byte is reached. If the length of the string stored in the {{password}} array is greater than the size of the {{buffer}} array, then a buffer overflow occurs.
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#include <stdio.h>
#include <ctype.h>
#include <string.h>
int do_auth(void) {
char *username;
char *password;
/* Get username and password from user, return -1 if invalid */
}
void report_error(const char *msg) {
const char *error_log;
char buffer[24];
sprintf(buffer, "Error: %s", error_log);
printf("%s\n", buffer);
}
int main(void) {
if (do_auth() == -1) {
report_error("Unable to login");
}
return 0;
}
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This rule appears in the C Secure Coding Standard as EXP33-C. Do not reference uninitialized memory.
Bibliography
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[ISO/IEC 14882-2003|AA. Bibliography#ISO/IEC 14882-2003]\] Section 8.5 Initializers.
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[Lockheed Martin 05|AA. Bibliography#Lockheed Martin 05] \] AV Rule 142 All variables shall be initialized before use.
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[[ISO/IEC PDTR 24772|AA. Bibliography#ISO/IEC PDTR 24772]\] "LAV Initialization of Variables"
\
[[mercy 06|AA. Bibliography#mercy 06]\]
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EXP32-CPP. Do not access a volatile object through a non-volatile reference 03. Expressions (EXP) EXP34-CPP. Ensure a null pointer is not dereferenced