Introduction:
Recently, an important vulnerability in the Linux kernel has been resolved. This vulnerability is related to the platform/x86 ideapad-laptop and addresses a NULL pointer dereference issue. Identified as CVE-2021-47079, the vulnerability could potentially have a significant impact on the systems running on Linux kernel versions prior to this fix. In this post, we'll delve into the details of this vulnerability, provide code snippets, and share links to the original references.

Vulnerability Details:

A NULL pointer dereference occurs when a program attempts to access or modify memory through a pointer variable that has not been properly initialized or has been set to NULL. In the context of CVE-2021-47079, the issue resides in the platform/x86: ideapad-laptop module in the Linux kernel. Specifically, the problem arises when the third parameter of the dytc_cql_command function is not initialized properly and is instead set to NULL, causing the function to crash when the parameter is dereferenced.

Here's a code snippet demonstrating the vulnerability

static int dytc_cql_command(struct ideapad_private *priv, u8 op, u8 *m,
                             unsigned long *value)
{
    int ret;
    
    /* The third parameter "m" is not checked for NULL before dereferencing it */
    
    ret = ideapad_dytc_cmd(priv, x55AA001 | (op << 8) | (*m << 16), value);
    if (ret || !dytc_sw_ok(priv))
        return -EIO;
    
    return ;
}

As we can see, the third parameter, m, is directly dereferenced without checking for NULL. A safer version of the code would provide a check for NULL before dereferencing the parameter:

static int dytc_cql_command(struct ideapad_private *priv, u8 op, u8 *m,
                             unsigned long *value)
{
    int ret;
    
    /* Check if the third parameter "m" is NULL before dereferencing it */
    if (!m)
        return -EINVAL;
    
    ret = ideapad_dytc_cmd(priv, x55AA001 | (op << 8) | (*m << 16), value);
    if (ret || !dytc_sw_ok(priv))
        return -EIO;
    
    return ;
}

By checking if the m parameter is NULL before using it, we can prevent the NULL pointer dereference vulnerability from occurring.

For more information on this vulnerability, you can refer to the following resources

1. The original patch commit that resolves this vulnerability in the Linux kernel can be found at: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=00dba22a5c69edde2b0091ccd28e5aa600b6039e

2. Detailed information about the CVE-2021-47079 vulnerability can be found on the CVE website: https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2021-47079

Conclusion:

In conclusion, the Linux kernel vulnerability CVE-2021-47079 has been resolved, addressing a NULL pointer dereference issue in the platform/x86 ideapad-laptop module. System administrators and users should apply the patch to ensure that their systems are protected against this vulnerability. Stay informed about the latest security vulnerabilities and updates to safeguard your systems and data effectively.

Timeline

Published on: 03/01/2024 22:15:47 UTC
Last modified on: 12/09/2024 18:41:59 UTC