Possibly wrong buffer size in string copy¶
ID: cpp/bad-strncpy-size
Kind: problem
Security severity: 9.3
Severity: warning
Precision: medium
Tags:
- reliability
- correctness
- security
- external/cwe/cwe-676
- external/cwe/cwe-119
- external/cwe/cwe-251
Query suites:
- cpp-security-extended.qls
- cpp-security-and-quality.qls
Click to see the query in the CodeQL repository
The standard library function strncpy copies a source string to a destination buffer. The third argument defines the maximum number of characters to copy and should be less than or equal to the size of the destination buffer. Calls of the form strncpy(dest, src, strlen(src)) or strncpy(dest, src, sizeof(src)) incorrectly set the third argument to the size of the source buffer. Executing a call of this type may cause a buffer overflow. Buffer overflows can lead to anything from a segmentation fault to a security vulnerability.
Recommendation¶
Check the highlighted function calls carefully, and ensure that the size parameter is derived from the size of the destination buffer, not the source buffer.
Example¶
In the following examples, the size of the source buffer is incorrectly used as a parameter to strncpy:
char src[256];
char dest1[128];
...
strncpy(dest1, src, sizeof(src)); // wrong: size of dest should be used
char *dest2 = (char *)malloc(sz1 + sz2 + sz3);
strncpy(dest2, src, strlen(src)); // wrong: size of dest should be used
The corrected version uses the size of the destination buffer, or a variable containing the size of the destination buffer as the size parameter to strncpy:
char src[256];
char dest1[128];
...
strncpy(dest1, src, sizeof(dest1)); // correct
size_t destSize = sz1 + sz2 + sz3;
char *dest2 = (char *)malloc(destSize);
strncpy(dest2, src, destSize); // correct
References¶
cplusplus.com: strncpy.
I. Gerg. An Overview and Example of the Buffer-Overflow Exploit. IANewsletter vol 7 no 4. 2005.
M. Donaldson. Inside the Buffer Overflow Attack: Mechanism, Method & Prevention. SANS Institute InfoSec Reading Room. 2002.
Common Weakness Enumeration: CWE-676.
Common Weakness Enumeration: CWE-119.
Common Weakness Enumeration: CWE-251.