A recent vulnerability found in the Linux kernel has garnered significant attention due to its potential exploitation in the form of a use-after-free (UAF) write bug. The vulnerability, identified as CVE-2024-26622, involves the tomoyo_write_control() function within the Tomoyo Linux Security Module (LSM) subsystem. This post aims to provide a detailed explanation of the exploit, its implications for the system, and the recent resolution. We'll also delve into the pertinent code snippets and reference the original research for further information.

Exploit Details

The UAF write vulnerability in the Linux kernel specifically affects the tomoyo_write_control() function. When write() is executed for long lines, head->write_buf is updated, and not properly fetched after head->io_sem is held. This issue subsequently leads to the use-after-free-write and double-free bugs as two or more concurrent write() requests can create inconsistent memory states or write to freed memory.

Resolution and Code Snippet

A recent patch to the Linux kernel addresses the aforementioned vulnerability by ensuring that head->write_buf is fetched after head->io_sem is held. This prevents the use-after-free-write and double-free issues from occurring. The following code snippet illustrates the changes made to fix this vulnerability:

// Original code:
write_len = tomoyo_write_control(head->write_buf, count);
if (write_len != count)
    goto out;

// Updated code:
down_write(&head->io_sem);
write_len = tomoyo_write_control(head->write_buf, count);
if (write_len != count) {
    up_write(&head->io_sem);
    goto out;
}

The updated code now includes the down_write() and up_write() functions to properly fetch head->write_buf after head->io_sem is held. This ensures that concurrent write() requests do not cause memory issues.

For additional information on CVE-2024-26622, the initial discovery of the vulnerability and the research behind it can be found at the following sources:

1. Official CVE-2024-26622 announcement
2. Linux kernel Github repository
3. Tomoyo LSM documentation

Conclusion

The CVE-2024-26622 vulnerability in the Linux kernel has been resolved with a recent patch addressing the UAF write bug within the tomoyo_write_control() function. By ensuring that head->write_buf is fetched after head->io_sem is held, the vulnerabilities and resulting memory issues are effectively avoided. Kernel developers and system administrators are advised to apply the patch to maintain a secure environment.

It's essential to stay up-to-date on patches and reports involving the Linux kernel, as vulnerabilities such as CVE-2024-26622 can have a significant impact on system stability and security. Be sure to review the original references for detailed information on this issue, and continually monitor new developments in Linux kernel security.

Timeline

Published on: 03/04/2024 07:15:11 UTC
Last modified on: 11/21/2024 09:02:42 UTC