CVE-2026-98804 in Linux
Summary
by MITRE • 10/18/2026
In the Linux kernel, the following vulnerability has been resolved:
net: page_pool: fix use-after-free in page_pool_recycle_ring_bulk()
With CONFIG_PAGE_POOL_STATS=y, page_pool_recycle_ring_bulk() updates the recycle stats after dropping the producer lock. If it just recycled the last inflight netmems of a pool being destroyed, page_pool_release() can pass its producer-lock barrier and free the pool before recycle_stat_add() runs.
Commit fcc680a647ba7 ("page_pool: allow mixing PPs within one bulk") moved this stat update after the unlock. Commit 271683bb2cf32 ("page_pool: Fix use-after-free in page_pool_recycle_in_ring") later added the barrier, but only fixed page_pool_recycle_in_ring(). Move the update back under the lock.
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Analysis
by VulDB Data Team • 10/18/2026
The Linux kernel network subsystem contains a critical memory safety vulnerability within the page pool implementation, specifically affecting the bulk recycling mechanism for network memory buffers. This issue arises in the function page_pool_recycle_ring_bulk when the configuration option CONFIG_PAGE_POOL_STATS is enabled. The core technical flaw involves a race condition caused by an incorrect ordering of operations relative to synchronization primitives. Specifically, the code updates recycle statistics after releasing the producer lock that protects the pool's internal state. In scenarios where the last inflight network memory buffers are being recycled from a pool that is simultaneously undergoing destruction, this timing gap allows for a use-after-free scenario. The page_pool_release function can acquire and pass its own barrier checks while holding or acquiring necessary locks, leading to the deallocation of the pool structure before the delayed statistic update operation completes. This creates a window where the recycling code attempts to access memory that has already been freed by the release routine, resulting in undefined behavior such as kernel crashes, data corruption, or potential privilege escalation if an attacker can influence the timing and allocation patterns.
The root cause of this vulnerability is traced back to specific commits aimed at optimizing performance and fixing related issues without fully addressing the synchronization implications for statistics updates. An earlier commit allowed mixing page pools within a single bulk operation but inadvertently moved the statistic update outside the critical section protected by the producer lock. A subsequent fix attempted to address use-after-free conditions in a different recycling path, page_pool_recycle_in_ring, by adding appropriate memory barriers and locking mechanisms. However, this fix was not applied consistently across all code paths involving bulk operations. The disparity between how single-item recycling and bulk recycling handle synchronization led to the residual vulnerability in the bulk function. By moving the statistic update back under the producer lock, the kernel ensures that the pool structure remains valid for the duration of any operation accessing its metadata or state, thereby eliminating the race condition where deallocation could occur concurrently with access.
From a security taxonomy perspective, this vulnerability is classified as CWE-416: Use After Free. This category encompasses situations where software continues to use memory after it has been freed, which can lead to crashes, data corruption, and arbitrary code execution depending on how the freed memory is reallocated and used by subsequent operations. In the context of network processing, such vulnerabilities are particularly dangerous because they reside in high-throughput paths that handle packet buffers frequently. The operational impact includes potential denial of service through kernel panics or oops messages when the invalid memory access occurs. Furthermore, if an attacker can control the contents of the freed memory region before it is reallocated for another purpose, there may be opportunities to exploit this state inconsistency to execute arbitrary code with kernel privileges. This aligns with ATT&CK techniques related to exploitation of binary vulnerabilities and potentially privilege escalation via local exploits targeting kernel subsystems.
Mitigation strategies primarily involve applying the upstream Linux kernel patch that corrects the locking order in page_pool_recycle_ring_bulk. System administrators should ensure their systems are updated with a kernel version that includes this fix, which typically involves updating to a stable release or backporting the specific commit if running an older supported LTS branch. For environments where immediate updates are not feasible, monitoring for unusual system behavior such as frequent reboots or log entries related to page pool errors can serve as an indicator of compromise attempts exploiting this flaw. Additionally, disabling CONFIG_PAGE_POOL_STATS in custom kernel builds removes the vulnerable code path entirely, although this may impact visibility into network buffer recycling metrics and is generally not recommended for production environments where observability is critical. The long-term resolution relies on maintaining rigorous synchronization practices across all variants of similar functions to prevent divergent behavior between single-item and bulk processing paths within shared subsystems.