CVE-2024-57940: Fixing the Infinite Loop in exfat_readdir() in the Linux Kernel

In the Linux kernel, a bug has been identified and fixed in the function exfat_readdir(), which is responsible for reading the contents of directories in an exFAT formatted file system. This vulnerability, labelled CVE-2024-57940, highlights a potential infinite loop issue that could cause system-wide problems, such as hanging other tasks like exfat_sync_fs(). In this post, we will explore the details of the vulnerability and discuss how it has been resolved.

Vulnerability Details

The bug arises when the file system is corrupted in such a way that a cluster is linked to itself in the cluster chain, and there is an unused directory entry in the cluster. Under these circumstances, the variable 'dentry' would not be incremented, leading to an infinite loop which cannot be mitigated by the condition 'dentry < max_dentries'. As a consequence, the s_lock will not be released, causing other tasks, like the previously mentioned exfat_sync_fs(), to potentially stall indefinitely.

Fixing the Vulnerability

To address this issue, the maintainers of the Linux kernel have introduced a patch that explicitly stops the traversal of the cluster chain when there is an unused directory entry in the cluster. This effectively avoids the infinite loop scenario, allowing the system to continue functioning as expected. Here's a code snippet from the patch that illustrates the fix:

// Add a check for unused directory entries while traversing the cluster chain.
if (is_exfat_dent_unused(denta)) {
    // Stop traversing if an unused entry is found.
    break;
}

// ... Rest of the function remains unchanged.

How to Apply the Patch

For system administrators and users, it's essential to keep your Linux kernel up-to-date with the latest patches and security fixes, such as this CVE-2024-57940 resolution. You can follow these steps to update your kernel to include the latest patches:

1. Check the Linux kernel mailing list archive here for the latest information on exFAT-related patches.
2. Obtain the specific patch (in this case, the patch for CVE-2024-57940).

Conclusion

In summary, the Linux kernel has fixed a potentially severe vulnerability (CVE-2024-57940) related to an infinite loop in the exfat_readdir() function. By staying informed and applying the latest patches to your kernel, you can help keep your systems secure and reliable.

Timeline

Published on: 01/21/2025 13:15:08 UTC
Last modified on: 02/02/2025 11:15:14 UTC