CVE-2024-50216 in Linux
Summary
by MITRE • 11/09/2024
In the Linux kernel, the following vulnerability has been resolved:
xfs: fix finding a last resort AG in xfs_filestream_pick_ag
When the main loop in xfs_filestream_pick_ag fails to find a suitable AG it tries to just pick the online AG. But the loop for that uses args->pag as loop iterator while the later code expects pag to be set. Fix this by reusing the max_pag case for this last resort, and also add a check for impossible case of no AG just to make sure that the uninitialized pag doesn't even escape in theory.
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Analysis
by VulDB Data Team • 10/08/2025
The vulnerability identified as CVE-2024-50216 resides within the Linux kernel's XFS filesystem implementation, specifically in the xfs_filestream_pick_ag function that governs allocation group selection for file operations. This flaw represents a critical issue in the kernel's storage management subsystem where improper handling of allocation group selection can lead to system instability and potential security implications. The vulnerability manifests when the primary algorithm for selecting an appropriate allocation group fails to locate a suitable candidate, triggering a fallback mechanism that contains a fundamental logical error in iterator management.
The technical flaw occurs within the xfs_filestream_pick_ag function where a loop designed to identify an online allocation group uses args->pag as its iteration variable, while subsequent code expects this variable to be properly initialized and set. This creates a scenario where an uninitialized or improperly managed pag variable can be dereferenced or used inappropriately, leading to potential memory corruption or system crashes. The issue stems from a code path that fails to properly initialize the pag variable before the fallback loop executes, creating a condition where the loop variable becomes invalid and could cause undefined behavior during filesystem operations. This type of vulnerability aligns with CWE-457: Use of Uninitialized Variable, which specifically addresses scenarios where variables are used without proper initialization.
The operational impact of this vulnerability extends beyond simple system crashes to potentially compromise the stability of storage operations within Linux systems running XFS filesystems. When the fallback mechanism triggers due to the inability to find suitable allocation groups, the improper handling of the pag variable can result in kernel panics, system lockups, or more subtle corruption that might not immediately manifest but could lead to data integrity issues. This vulnerability affects systems where XFS is actively used for file storage operations, particularly in enterprise environments where storage reliability is critical. The issue could be exploited by malicious actors to cause denial of service conditions or potentially create opportunities for privilege escalation if the kernel memory corruption leads to code execution vulnerabilities.
The fix implemented addresses this vulnerability by reusing the existing max_pag case logic for the last resort allocation group selection, ensuring that proper initialization occurs before the fallback loop executes. Additionally, the patch introduces a theoretical check for impossible cases where no allocation groups exist, preventing any potential escape of uninitialized variables. This remediation aligns with defensive programming practices and follows the principle of least privilege by ensuring that all variables are properly initialized before use. The solution demonstrates adherence to kernel security standards and follows the established patterns for handling edge cases in kernel-space memory management. Organizations should prioritize applying this patch to maintain system stability and prevent potential exploitation of the uninitialized variable condition that could lead to system-wide disruptions in environments utilizing XFS filesystems. The vulnerability's resolution reinforces the importance of proper iterator management and variable initialization in kernel code, particularly in critical subsystems that handle file system operations and memory allocation.