CVE-2024-50219 in Linux
Summary
by MITRE • 11/09/2024
In the Linux kernel, the following vulnerability has been resolved:
mm/page_alloc: let GFP_ATOMIC order-0 allocs access highatomic reserves
Under memory pressure it's possible for GFP_ATOMIC order-0 allocations to fail even though free pages are available in the highatomic reserves. GFP_ATOMIC allocations cannot trigger unreserve_highatomic_pageblock() since it's only run from reclaim.
Given that such allocations will pass the watermarks in __zone_watermark_unusable_free(), it makes sense to fallback to highatomic reserves the same way that ALLOC_OOM can.
This fixes order-0 page allocation failures observed on Cloudflare's fleet when handling network packets:
kswapd1: page allocation failure: order:0, mode:0x820(GFP_ATOMIC), nodemask=(null),cpuset=/,mems_allowed=0-7 CPU: 10 PID: 696 Comm: kswapd1 Kdump: loaded Tainted: G O 6.6.43-CUSTOM #1 Hardware name: MACHINE Call Trace: dump_stack_lvl+0x3c/0x50 warn_alloc+0x13a/0x1c0 __alloc_pages_slowpath.constprop.0+0xc9d/0xd10 __alloc_pages+0x327/0x340 __napi_alloc_skb+0x16d/0x1f0 bnxt_rx_page_skb+0x96/0x1b0 [bnxt_en]
bnxt_rx_pkt+0x201/0x15e0 [bnxt_en]
__bnxt_poll_work+0x156/0x2b0 [bnxt_en]
bnxt_poll+0xd9/0x1c0 [bnxt_en]
__napi_poll+0x2b/0x1b0 bpf_trampoline_6442524138+0x7d/0x1000 __napi_poll+0x5/0x1b0 net_rx_action+0x342/0x740 handle_softirqs+0xcf/0x2b0 irq_exit_rcu+0x6c/0x90 sysvec_apic_timer_interrupt+0x72/0x90
[[email protected]: update comment]
Link: https://lkml.kernel.org/r/[email protected]
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Analysis
by VulDB Data Team • 07/16/2025
The vulnerability in question affects the Linux kernel's memory management subsystem, specifically within the page allocation mechanism under high memory pressure conditions. This issue manifests when GFP_ATOMIC order-0 allocations fail despite sufficient free pages being available in the highatomic reserves. The problem stems from a design gap where these critical allocations cannot access the highatomic reserves that are typically available during low memory scenarios, leading to unexpected allocation failures.
The technical flaw resides in how the kernel handles memory allocation decisions during periods of contention. When memory pressure occurs, the system should allow GFP_ATOMIC allocations to utilize highatomic reserves as a fallback mechanism similar to how ALLOC_OOM operations handle such situations. The current implementation fails to consider that these atomic allocations might still require access to highatomic reserves even when they don't trigger the reclaim process that normally handles such fallbacks.
This vulnerability directly impacts network packet processing on Cloudflare's infrastructure, where the failure occurs during packet reception handling through the bnxt_en driver. The allocation failure path shows kswapd1 attempting to allocate a page with GFP_ATOMIC flags while processing network packets, indicating this affects high-priority system operations that cannot afford allocation failures. The call trace demonstrates how the failure propagates through network interrupt handling code, specifically through __napi_alloc_skb and related driver functions.
The operational impact of this vulnerability is significant for systems under memory pressure, particularly those handling high volumes of network traffic or real-time processing requirements. When GFP_ATOMIC allocations fail, it can lead to packet drops, service interruptions, and degraded performance in network-intensive applications. This affects the reliability of critical infrastructure components that depend on atomic memory allocation semantics for maintaining system stability during resource contention.
The mitigation approach involves modifying the page allocation logic to allow GFP_ATOMIC order-0 allocations to fall back to highatomic reserves when normal watermarks are passed, similar to how ALLOC_OOM operations handle such scenarios. This change aligns the behavior with expected kernel memory management patterns and ensures that critical atomic allocations have access to appropriate reserve resources during memory pressure conditions. The fix addresses a fundamental mismatch between allocation semantics and available resource access during system stress periods.
This vulnerability relates to CWE-476 which deals with NULL Pointer Dereference, though more specifically it represents a resource exhaustion or allocation failure scenario that impacts system stability. From an ATT&CK perspective, this could be categorized under privilege escalation or denial of service techniques when the allocation failures cascade into broader system instability. The fix ensures proper handling of memory allocation boundaries during high-pressure scenarios and aligns with kernel security best practices for resource management under stress conditions.
The resolution demonstrates a critical understanding of how different allocation flags should interact with system memory reserves, particularly in high-priority atomic operations that cannot afford to fail even when other resources appear available. This change improves the robustness of kernel memory management by ensuring consistent behavior across different allocation types during memory pressure scenarios. The fix also reinforces proper handling of memory allocation failure paths and ensures that critical system operations maintain their expected behavior regardless of underlying resource contention levels.