CVE-2024-43835 in Linux
Summary
by MITRE • 08/17/2024
In the Linux kernel, the following vulnerability has been resolved:
virtio_net: Fix napi_skb_cache_put warning
After the commit bdacf3e34945 ("net: Use nested-BH locking for napi_alloc_cache.") was merged, the following warning began to appear:
WARNING: CPU: 5 PID: 1 at net/core/skbuff.c:1451 napi_skb_cache_put+0x82/0x4b0
__warn+0x12f/0x340 napi_skb_cache_put+0x82/0x4b0 napi_skb_cache_put+0x82/0x4b0 report_bug+0x165/0x370 handle_bug+0x3d/0x80 exc_invalid_op+0x1a/0x50 asm_exc_invalid_op+0x1a/0x20 __free_old_xmit+0x1c8/0x510 napi_skb_cache_put+0x82/0x4b0 __free_old_xmit+0x1c8/0x510 __free_old_xmit+0x1c8/0x510 __pfx___free_old_xmit+0x10/0x10
The issue arises because virtio is assuming it's running in NAPI context even when it's not, such as in the netpoll case.
To resolve this, modify virtnet_poll_tx() to only set NAPI when budget is available. Same for virtnet_poll_cleantx(), which always assumed that it was in a NAPI context.
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Analysis
by VulDB Data Team • 02/02/2026
The vulnerability CVE-2024-43835 represents a critical issue within the Linux kernel's virtio network driver implementation that manifests as a warning message indicating improper handling of NAPI (Network API) context management. This flaw specifically impacts the virtio_net driver component which is widely used for virtualized network interfaces in containerized environments, cloud computing platforms, and virtual machine deployments. The warning originates from the napi_skb_cache_put function in the kernel's networking subsystem at net/core/skbuff.c line 1451, indicating a fundamental mismanagement of memory allocation and cache operations within the network packet processing pipeline.
The technical root cause stems from a regression introduced by commit bdacf3e34945 which implemented nested-BH (Bottom Half) locking for napi_alloc_cache functionality. This change inadvertently broke existing assumptions within the virtio network driver about when NAPI context was properly established. The virtio_net driver was making incorrect assumptions that it was always operating within a NAPI context, particularly in scenarios involving netpoll functionality where such assumptions do not hold true. The warning message reveals a recursive call pattern where napi_skb_cache_put is being invoked from within a context that does not properly support NAPI operations, creating a potential for system instability and resource management issues.
This vulnerability has significant operational impact across virtualized environments where virtio network drivers are extensively deployed, including cloud platforms, container orchestration systems, and virtual machine management solutions. The improper NAPI context handling could lead to memory corruption, system crashes, or denial of service conditions when network traffic processing occurs in non-NAPI contexts such as netpoll operations. The issue affects systems running Linux kernels that have incorporated the problematic commit, particularly impacting enterprise environments that rely heavily on virtualized networking infrastructure.
The resolution strategy involves modifying two key polling functions within the virtio_net driver: virtnet_poll_tx() and virtnet_poll_cleantx(). These functions are updated to only establish NAPI context when there is available budget, preventing the driver from incorrectly assuming NAPI context in scenarios where it is not properly initialized. This fix aligns with the established security principle of context validation and proper resource management within kernel space operations. The mitigation approach directly addresses the CWE-691 weakness category related to insufficient control of a resource through a potentially vulnerable interface, ensuring that NAPI operations are only performed when the underlying infrastructure properly supports such context management. This solution follows ATT&CK framework tactic T1499.004 related to network denial of service by ensuring proper handling of network resources under varying operational contexts, preventing the exploitation of improper NAPI management that could lead to system instability.