CVE-2024-26686 in Linux
Summary
by MITRE • 04/03/2024
In the Linux kernel, the following vulnerability has been resolved:
fs/proc: do_task_stat: use sig->stats_lock to gather the threads/children stats
lock_task_sighand() can trigger a hard lockup. If NR_CPUS threads call do_task_stat() at the same time and the process has NR_THREADS, it will spin with irqs disabled O(NR_CPUS * NR_THREADS) time.
Change do_task_stat() to use sig->stats_lock to gather the statistics outside of ->siglock protected section, in the likely case this code will run lockless.
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Analysis
by VulDB Data Team • 07/17/2025
The vulnerability identified as CVE-2024-26686 represents a critical performance degradation and potential system instability issue within the Linux kernel's process statistics gathering mechanism. This flaw specifically affects the fs/proc subsystem where the do_task_stat() function is responsible for collecting thread and child process statistics. The vulnerability manifests when multiple threads simultaneously attempt to access process statistics, creating a scenario that can lead to system-wide lockups and denial of service conditions. The root cause lies in the improper locking mechanism used during statistics collection, where the existing implementation relies on lock_task_sighand() which can trigger hard lockups under concurrent access conditions.
The technical implementation of this vulnerability stems from the kernel's handling of signal statistics locks within the process management subsystem. When numerous threads call do_task_stat() concurrently while a process has many threads, the system enters a spinlock scenario with interrupts disabled for an extended period proportional to the product of NR_CPUS and NR_THREADS. This creates a pathological scaling issue where the computational overhead grows exponentially with system load, effectively grinding the system to a halt. The vulnerability specifically targets the synchronization primitives used in signal handling and process statistics collection, where the traditional approach of using lock_task_sighand() proves inadequate under high concurrency conditions.
The operational impact of CVE-2024-26686 extends beyond simple performance degradation to encompass potential system crashes and complete denial of service conditions. Systems running under high thread load or with processes containing many child threads become particularly vulnerable to this condition, as the spinlock behavior with disabled interrupts can cause the entire system to become unresponsive. This vulnerability affects any Linux system where the proc filesystem is actively used for process monitoring and statistics gathering, making it particularly dangerous in production environments where system stability is paramount. The risk is amplified in multi-core systems where the probability of multiple threads accessing the same process statistics simultaneously increases significantly.
The mitigation strategy for this vulnerability involves implementing a redesign of the statistics gathering mechanism to eliminate the problematic locking pattern. The fix introduces the use of sig->stats_lock for collecting thread and child statistics outside of the traditional siglock protected section, enabling lockless operation in most cases. This approach aligns with established best practices for concurrent programming in kernel space, where minimizing lock acquisition time and avoiding nested locking scenarios are critical for system performance. The solution addresses the core issue identified in CWE-664, which deals with improper control of a resource through time-of-check to time-of-use vulnerabilities, and follows ATT&CK technique T1499.001 for resource exhaustion attacks. By moving statistics gathering outside the critical section, the kernel avoids the hard lockup scenario while maintaining data consistency through appropriate locking mechanisms that don't block multiple concurrent access patterns.