CWE Rule 240

Improper Handling of Inconsistent Structural Elements

Since R2024a

Description

Rule Description

The product does not handle or incorrectly handles when two or more structural elements should be consistent, but are not.

Polyspace Implementation

The rule checker checks for Mismatch between data length and size.

Examples

Mismatch between data length and size

Issue

This issue occurs when you do not check the length argument and data buffer argument of memory copying functions such as memcpy, memset, or memmove, to protect against buffer overflows.

Risk

If an attacker can manipulate the data buffer or length argument, the attacker can cause buffer overflow by making the actual data size smaller than the length.

This mismatch in length allows the attacker to copy memory past the data buffer to a new location. If the extra memory contains sensitive information, the attacker can now access that data.

This defect is similar to the SSL Heartbleed bug.

Fix

When copying or manipulating memory, compute the length argument directly from the data so that the sizes match.

Example — Copy Buffer of Data

#include <stdlib.h>
#include <string.h>

typedef struct buf_mem_st {
    char *data;
    size_t max;     /* size of buffer */
} BUF_MEM;

extern BUF_MEM beta;

int cpy_data(BUF_MEM *alpha)
{
    BUF_MEM *os = alpha;
    int num, length;

    if (alpha == 0x0) return 0;
    num = 0;

    length = *(unsigned short *)os->data;
    memcpy(&(beta.data[num]), os->data + 2, length); //Noncompliant

    return(1);
}

This function copies the buffer alpha into a buffer beta. However, the length variable is not related to data+2.

Correction — Check Buffer Length

One possible correction is to check the length of your buffer against the maximum value minus 2. This check ensures that you have enough space to copy the data to the beta structure.

#include <stdlib.h>
#include <string.h>

typedef struct buf_mem_st {
    char *data;
    size_t max;     /* size of buffer */
} BUF_MEM;

extern BUF_MEM beta;

int cpy_data(BUF_MEM *alpha)
{
    BUF_MEM *os = alpha;
    int num, length;

    if (alpha == 0x0) return 0;
    num = 0;

    length = *(unsigned short *)os->data;
    if (length<(os->max -2)) {
        memcpy(&(beta.data[num]), os->data + 2, length); 
    }

    return(1);

}

Check Information

Category: Others

Version History

Introduced in R2024a