CVE-2026-64457 in Linux
Summary
by MITRE • 07/25/2026
In the Linux kernel, the following vulnerability has been resolved:
virtio_pci: fix vq info pointer lookup via wrong index
Unbinding a virtio balloon device:
echo virtio0 > /sys/bus/virtio/drivers/virtio_balloon/unbind
triggers a NULL pointer dereference. The dmesg says:
BUG: kernel NULL pointer dereference, address: 0000000000000008 [...]
RIP: 0010:__list_del_entry_valid_or_report+0x5/0xf0 Call Trace: <TASK> vp_del_vqs+0x121/0x230 remove_common+0x135/0x150 virtballoon_remove+0xee/0x100 virtio_dev_remove+0x3b/0x80 device_release_driver_internal+0x187/0x2c0 unbind_store+0xb9/0xe0 kernfs_fop_write_iter.llvm.11660790530567441834+0xf6/0x180 vfs_write+0x2a9/0x3b0 ksys_write+0x5c/0xd0 do_syscall_64+0x54/0x230 entry_SYSCALL_64_after_hwframe+0x29/0x31 [...]
</TASK>
The virtio_balloon device registers 5 queues (inflate, deflate, stats, free_page, reporting) but only the first two are unconditional. The stats, free_page and reporting queues are each conditional on their respective feature bits. When any of these features are absent, the corresponding vqs_info entry has name == NULL, creating holes in the array.
The root cause is an indexing mismatch introduced when vq info storage was changed to be passed as an argument. vp_find_vqs_msix() and vp_find_vqs_intx() store the info pointer at vp_dev->vqs[i], where 'i'
is the caller's sparse array index. However, the virtqueue itself gets vq->index assigned from queue_idx, a dense index that skips NULL entries. When holes exist, 'i' and queue_idx diverge. Later, vp_del_vqs() looks up info via vp_dev->vqs[vq->index] using the dense
index into the sparsely-populated array, and hits NULL.
Fix this by storing info at vp_dev->vqs[queue_idx] instead of
vp_dev->vqs[i], so the store index matches the lookup index
(vq->index). Apply the fix to both the MSIX and INTX paths.
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Analysis
by VulDB Data Team • 07/25/2026
This vulnerability exists within the linux kernel's virtio pci driver implementation, specifically affecting the virtio balloon device management functionality. The flaw manifests as a null pointer dereference when attempting to unbind a virtio balloon device through the sysfs interface, creating a critical kernel panic condition that can lead to system instability and potential denial of service attacks. The vulnerability stems from an indexing inconsistency in how virtqueue information is stored and retrieved within the driver's internal data structures.
The technical root cause involves a mismatch between sparse array indexing and dense queue indexing mechanisms within the virtio pci subsystem. When a virtio balloon device registers its queues, it creates five distinct virtqueues including inflate, deflate, stats, free_page, and reporting queues. However, only the first two queues are always present while the remaining three are conditionally enabled based on feature bits. This conditional registration creates gaps in the array structure where entries have name == NULL, forming holes that disrupt normal indexing operations.
The vulnerability occurs during the device removal process when the vp_del_vqs() function attempts to clean up virtqueue resources. The driver stores virtqueue information pointers at positions corresponding to the sparse array index vp_dev->vqs[i] where 'i' represents the position in the sparse array structure. However, the actual virtqueue objects receive their index assignments from queue_idx which represents a dense indexing scheme that skips over NULL entries. This fundamental mismatch means that when vp_del_vqs() attempts to access the stored information using vq->index as the lookup key, it accesses an invalid memory location corresponding to a NULL entry in the sparse array, resulting in the kernel null pointer dereference.
This vulnerability directly maps to CWE-476 which describes NULL Pointer Dereference conditions in software systems. The attack vector is facilitated through legitimate system interfaces using standard sysfs operations that are part of normal device management workflows. The impact extends beyond simple denial of service as this represents a potential privilege escalation path since kernel memory corruption can be exploited by malicious actors with access to the system.
The mitigation strategy involves correcting the indexing mechanism by ensuring that virtqueue information is stored at vp_dev->vqs[queue_idx] rather than vp_dev->vqs[i], aligning the storage index with the lookup index used by vq->index. This fix must be applied consistently across both MSI-X and legacy interrupt handling paths to ensure complete coverage of all affected code branches. The solution addresses the fundamental architectural inconsistency without altering the functional behavior of the virtio subsystem, maintaining backward compatibility while preventing the kernel crash condition.
The vulnerability demonstrates a classic software engineering flaw in data structure management where assumptions about array indexing were not properly validated against dynamic allocation patterns. This type of issue commonly appears in kernel drivers where complex resource management and conditional feature support create sparse data structures that require careful index handling to prevent memory access violations. The fix represents a straightforward but critical correction that ensures proper synchronization between storage and retrieval mechanisms in the driver's internal data management system, aligning with best practices for kernel memory safety as recommended by the Linux kernel security team and documented in standard secure coding guidelines.