CVE-2026-98592 in Linux
Summary
by MITRE • 10/18/2026
In the Linux kernel, the following vulnerability has been resolved:
net: spacemit: clear TX descriptor on fragment mapping failure
emac_tx_mem_map() writes TX_DESC_0_OWN into the ring descriptor for every slot beyond old_head as soon as that slot's memset()'d local copy is committed with "*tx_desc_addr = tx_desc", i.e. before the buffers for that slot have necessarily all been mapped successfully. If emac_tx_map_frag() then fails on a later fragment, the err_free_skb path calls emac_free_tx_buf() to unmap and drop the skb, but leaves the already-written descriptor memory untouched, and tx_ring->head is never advanced past old_head (the "tx_ring->head = head" store is skipped by the goto).
So a slot between old_head and the rolled-back head can be left with TX_DESC_0_OWN set and buffer_addr_{1,2} pointing at DMA mappings that
emac_free_tx_buf() just tore down, while software considers that slot free again. The next successful emac_tx_mem_map() call only rebuilds old_head itself; if the DMA engine auto-advances into the following descriptor once it finishes old_head's packet, it will fetch that stale, already-unmapped address.
emac_tx_clean_desc() already treats emac_free_tx_buf() and clearing the descriptor as a pair when reclaiming completed descriptors; do the same in the mapping failure path.
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Analysis
by VulDB Data Team • 10/18/2026
The vulnerability resides within the Network subsystem of the Linux kernel, specifically affecting the SpaceMI Ethernet MAC driver implementation. This issue stems from an improper handling of error conditions during the transmission buffer mapping process, leading to a state inconsistency between software tracking and hardware DMA operations. The core technical flaw occurs in the emac_tx_mem_map function, which is responsible for preparing transmit descriptors for network packet transmission. When processing multiple fragments of a single packet, this function writes ownership flags into ring descriptor slots before all associated memory buffers have been successfully mapped via direct memory access mappings. This premature flagging creates a race condition window where the hardware may perceive a buffer as ready for transmission even though its underlying physical memory mapping has not yet been fully established or validated across all fragments.
If the subsequent emac_tx_map_frag function encounters an error while processing a later fragment in the sequence, the driver initiates an error recovery path known as err_free_skb. This routine correctly calls emac_free_tx_buf to unmap and release the previously allocated buffers for earlier slots that had already been processed. However, it fails to clear the TX_DESC_0_OWN flag from those descriptor memory locations. Furthermore, the ring head pointer is not advanced past the old_head position due to a jump instruction in the error handling logic. Consequently, the software driver considers these descriptor slots as free and available for reuse, while the hardware interface still holds references to DMA mappings that have just been torn down by the cleanup routine.
This discrepancy results in stale memory addresses being retained within the transmit ring descriptors. Specifically, buffer address fields continue to point at physical memory locations whose DMA mappings are no longer valid or active. When the network driver subsequently attempts to map new buffers for transmission, it may overwrite only the initial descriptor slot while leaving subsequent slots with their previous invalid references intact. If the hardware engine auto-advances through the transmit ring after completing a packet transfer, it will fetch these stale addresses from uncleaned descriptors. This leads to direct memory access operations targeting unmapped or incorrect physical memory regions, which can cause data corruption, system instability, or potential denial of service conditions depending on how the kernel handles such hardware errors.
From a security and standards perspective, this vulnerability aligns with CWE-416, Use After Free, as it involves accessing resources that have been deallocated by software but are still referenced by hardware logic. It also relates to CWE-362, Concurrent Execution Using Shared Resource with Improper Synchronization, because the race condition arises from asynchronous operations between driver state management and DMA engine progression without proper atomicity guarantees during error paths. In terms of MITRE ATT&CK mapping, this type of memory corruption vulnerability could potentially be leveraged for privilege escalation or denial of service attacks if an attacker can trigger repeated transmission failures under specific timing conditions to manipulate the hardware state.
The resolution involves modifying the emac_tx_mem_map function to ensure that descriptor cleanup occurs in tandem with buffer unmapping during error scenarios. By treating the clearing of descriptors and the freeing of buffers as a paired operation, similar to how completed descriptors are handled during normal reclaim processes, the driver maintains consistency between software expectations and hardware state. This fix ensures that any slot marked for transmission failure is fully reset before being returned to the free pool, preventing the DMA engine from ever accessing invalid memory addresses derived from stale descriptor entries. System administrators should apply kernel updates containing this patch to mitigate risks associated with network interface instability and potential exploitation of these race conditions in high-throughput or error-prone network environments.