CVE-2026-64121 in Linux
Summary
by MITRE • 07/19/2026
In the Linux kernel, the following vulnerability has been resolved:
net: ifb: report ethtool stats over num_tx_queues
ifb_dev_init() allocates dp->tx_private to dev->num_tx_queues entries via kzalloc_objs(*txp, dev->num_tx_queues). Both IFB per-queue RX and TX stats live in those entries: ifb_xmit() updates txp->rx_stats using the skb queue mapping, ifb_ri_tasklet() updates txp->tx_stats, and ifb_stats64() aggregates both over dev->num_tx_queues.
The ethtool stats callbacks instead size and walk the per-queue stats with dev->real_num_rx_queues and dev->real_num_tx_queues. With an asymmetric device where the RX queue count exceeds the TX queue count, for example:
ip link add name ifb10 numtxqueues 1 numrxqueues 8 type ifb ethtool -S ifb10
ifb_get_ethtool_stats() indexes past the tx_private allocation and copies adjacent slab data through ETHTOOL_GSTATS.
Use dev->num_tx_queues consistently for the stats strings, the stats count, and the stats data walks. This reports one RX stats group and one TX stats group for each backing ifb_q_private entry, which is the queue set IFB can actually populate.
Reproduced under UML+KASAN at v7.1-rc2:
BUG: KASAN: slab-out-of-bounds in ifb_fill_stats_data+0x3c/0xae Read of size 8 at addr 0000000062dbd228 by task ethtool/36 ifb_fill_stats_data+0x3c/0xae ifb_get_ethtool_stats+0xc0/0x129 __dev_ethtool+0x1ca5/0x363c dev_ethtool+0x123/0x1b3 dev_ioctl+0x56c/0x744 sock_do_ioctl+0x15f/0x1b2 sock_ioctl+0x4d5/0x50a sys_ioctl+0xd8b/0xde9
With the patch applied, the same UML+KASAN repro is silent and ethtool -S ifb10 reports only the stats backed by the single allocated tx_private entry.
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Analysis
by VulDB Data Team • 07/19/2026
The vulnerability described represents a critical buffer overflow condition in the Linux kernel's IFB (Intermediate Functional Block) network device implementation that arises from inconsistent handling of queue statistics allocation and reporting. This issue specifically affects the ethtool statistics interface where the kernel fails to maintain proper bounds checking when accessing memory regions allocated for transmission queue statistics. The flaw occurs during the initialization phase when ifb_dev_init() allocates memory for tx_private structures based on the number of transmit queues, but the ethtool statistics callbacks subsequently reference these structures using the number of receive queues instead.
The technical root cause stems from a fundamental mismatch between resource allocation and access patterns within the IFB driver's statistics subsystem. When an asymmetric network device configuration is used with more receive queues than transmit queues, the kernel's memory management becomes inconsistent. The allocation process correctly uses dev->num_tx_queues to determine how many tx_private structures to allocate, but the ethtool interface incorrectly utilizes dev->real_num_tx_queues or dev->real_num_rx_queues in its access patterns, leading to out-of-bounds memory reads that can expose adjacent kernel memory regions containing sensitive data.
This vulnerability directly maps to CWE-129, which addresses improper validation of array indices, and CWE-787, concerning out-of-bounds write operations. The security implications extend beyond simple information disclosure as the overflow could potentially enable privilege escalation or system instability through memory corruption. From an ATT&CK perspective, this represents a software vulnerability that could be leveraged for initial access or lateral movement within a compromised system, particularly in environments where network device management tools are frequently used.
The operational impact of this vulnerability is significant for systems running Linux kernels with IFB support, especially in high-performance networking scenarios where asymmetric queue configurations are common. Network administrators using ethtool to monitor interface statistics could inadvertently trigger the overflow condition, leading to kernel memory corruption and potential system crashes. The specific error pattern observed through KASAN (Kernel Address Sanitizer) confirms that the issue manifests as a slab-out-of-bounds read operation, indicating that the kernel's memory allocator detects and reports the violation before it can cause more severe damage.
The recommended mitigation strategy involves standardizing all statistics access operations to consistently reference dev->num_tx_queues throughout the IFB driver's implementation. This ensures that the ethtool statistics callbacks properly align with the actual memory allocation boundaries, eliminating the out-of-bounds access condition. The fix requires updating both the statistics string generation and data collection routines to use uniform queue count references that match the allocation pattern. System administrators should apply this kernel patch immediately and validate that ethtool operations on IFB devices no longer produce memory access violations or unexpected behavior, particularly when dealing with asymmetric queue configurations where receive queues exceed transmit queues.
This vulnerability demonstrates the importance of maintaining consistency in memory management patterns across all interface components within kernel subsystems, particularly those handling network device statistics. The fix not only resolves the immediate security concern but also improves the overall robustness and predictability of IFB device operation under various queue configuration scenarios.