CVE-2026-98508 in Linux
Summary
by MITRE • 10/18/2026
In the Linux kernel, the following vulnerability has been resolved:
drm/virtio: fix NULL pointer dereference on fence allocation failure
virtio_gpu_fence_alloc() can fail due to memory pressure and return NULL, but its caller like virtio_gpu_init_submit() never checks it. Later, virtio_gpu_init_submit() passes the NULL fence to virtio_gpu_fence_event_create(), which unconditionally dereferences it.
Found when fuzzing the virtio driver with Syzkaller:
Oops: general protection fault, probably for non-canonical address 0xdffffc0000000012: 0000 [#1] SMP KASAN NOPTI
KASAN: null-ptr-deref in range [0x0000000000000090-0x0000000000000097]
CPU: 1 UID: 0 PID: 9991 Comm: syz.0.121 Not tainted 7.2.0 #4 PREEMPT(full) Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.17.0-0-gb52ca86e094d-prebuilt.qemu.org 04/01/2014 RIP: 0010:virtio_gpu_fence_event_create drivers/gpu/drm/virtio/virtgpu_submit.c:295 [inline]
RIP: 0010:virtio_gpu_init_submit drivers/gpu/drm/virtio/virtgpu_submit.c:398 [inline]
RIP: 0010:virtio_gpu_execbuffer_ioctl+0xc78/0x1aa0 drivers/gpu/drm/virtio/virtgpu_submit.c:505 Code: 85 ed 0f 85 21 09 00 00 e8 05 5a c9 fb 48 8b 44 24 10 48 8d b8 90 00 00 00 48 b8 00 00 00 00 00 fc ff df 48 89 fa 48 c1 ea 03 <80> 3c 02 00 0f 85 9a 0d 00 00 48 8b 44 24 10 4c 89 b0 90 00 00 00 RSP: 0018:ffffc900039dfad0 EFLAGS: 00010216 RAX: dffffc0000000000 RBX: ffffc900039dfdd8 RCX: ffffffff85f6fd3d RDX: 0000000000000012 RSI: ffffffff85f6fd4b RDI: 0000000000000090 RBP: 0000000000000000 R0virtio_gpu_virgl_process_cmd: ctrl 0x102, error 0x1203 R10: 0000000000000000 R11: 0000000000000000 R12: ffff8880132c4000 R13: 0000000000000000 R14: ffff888073b6c700 R15: 000000000000003b FS: 00007fab480b96c0(0000) GS:ffff8880eb6e9000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00007effbf5e55a8 CR3: 0000000048d19000 CR4: 0000000000350ef0 Call Trace: <TASK> drm_ioctl_kernel+0x1f4/0x3e0 drivers/gpu/drm/drm_ioctl.c:817 drm_ioctl+0x5f4/0xc70 drivers/gpu/drm/drm_ioctl.c:914 vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:597 [inline]
__se_sys_ioctl fs/ioctl.c:583 [inline]
__x64_sys_ioctl+0x18e/0x210 fs/ioctl.c:583 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x116/0x800 arch/x86/entry/syscall_64.c:94 entry_SYSCALL_64_after_hwframe+0x77/0x7f RIP: 0033:0x7fab471a82bd Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 90 f3 0f 1e fa 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 b0 ff ff ff f7 d8 64 89 01 48 RSP: 002b:00007fab480b9018 EFLAGS: 00000246 ORIG_RAX: 0000000000000010 RAX: ffffffffffffffda RBX: 00007fab47435fa0 RCX: 00007fab471a82bd RDX: 00002000000000c0 RSI: 00000000c0406442 RDI: 0000000000000003 RBP: 00007fab480b9080 R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000001 R13: 00007fab47436038 R14: 00007fab47435fa0 R15: 00007ffe85ab0740 </TASK> Modules linked in: ---[ end trace 0000000000000000 ]---
RIP: 0010:virtio_gpu_fence_event_create drivers/gpu/drm/virtio/virtgpu_submit.c:295 [inline]
RIP: 0010:virtio_gpu_init_submit drivers/gpu/drm/virtio/virtgpu_submit.c:398 [inline]
RIP: 0010:virtio_gpu_execbuffer_ioctl+0xc78/0x1aa0 drivers/gpu/drm/virtio/virtgpu_submit.c:505 Code: 85 ed 0f 85 21 09 00 00 e8 05 5a c9 fb 48 8b 44 24 10 48 8d b8 90 00 00 00 48 b8 00 00 00 00 00 fc ff df 48 89 fa 48 c1 ea 03 <80> 3c 02 00 0f 85 9a 0d 00 00 48 8b 44 24 10 4c 89 b0 90 00 00 00 RSP: 0018:ffffc900039dfad0 EFLAGS: 00010216 RAX: dffffc0000000000 RBX: ffffc900039dfdd8 RCX: ffffffff85f6fd3d RDX: 0000000000000012 RSI: ffffffff85f6fd4b RDI: 0000000000000090 RBP: 0000000000000000 R08: 0000000000000005 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000000 R12: ffff8880132c4000 R13: 0000000000000000 R14: ffff888073b6c700 R15: 000000000000003b FS: 00007fab480b96c0(0000) GS:ffff888098ae9000(0000) knlGS:00000000 ---truncated---
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Analysis
by VulDB Data Team • 10/19/2026
The Linux kernel's virtio GPU driver contains a critical null pointer dereference vulnerability within the fence allocation and submission logic. This flaw originates in the function virtio_gpu_fence_alloc, which is responsible for allocating memory structures used to track graphics command completion via fences. Under conditions of high system memory pressure or resource exhaustion, this allocation routine may fail and return a NULL pointer instead of a valid memory address. The core issue lies in the subsequent handling by its caller, specifically the function virtio_gpu_init_submit, which fails to validate the return value from the allocation call before proceeding with execution. This lack of defensive programming allows the control flow to continue despite the absence of necessary resources, leading directly into deeper kernel operations that assume a valid object exists.
The operational impact manifests when the NULL pointer is passed further down the call stack to virtio_gpu_fence_event_create. This function unconditionally attempts to dereference the fence structure to access its members and initialize event handling mechanisms. Because the input is null, this action triggers an immediate general protection fault within kernel space. The resulting crash results in a system panic or kernel oops, effectively causing a denial of service for any process relying on virtualized graphics acceleration via virtio. Since this code path can be triggered through standard ioctl calls from user-space applications interacting with the DRM subsystem, a local unprivileged attacker could potentially exploit this condition to destabilize the host operating system if they have access to the GPU device node and can induce memory pressure or trigger specific allocation patterns that lead to failure.
From a technical classification perspective, this vulnerability is categorized under CWE-476, which denotes NULL Pointer Dereference. The root cause is identified as CWE-252, Checkpoint Failure, where the software fails to check for an error condition after calling a function that can fail. In terms of attack vectors and techniques, this aligns with MITRE ATT&CK technique T1053, specifically Scheduled Task/Job or System Services if viewed through the lens of persistence, but more accurately fits into lateral movement or local privilege escalation contexts where system stability is targeted to facilitate other attacks. The specific trigger mechanism involves ioctl calls mapped in the Linux kernel's DRM subsystem, which corresponds to ATT&CK technique T1059 within command and script interpretation vectors when considering how user-space applications invoke these driver functions.
Mitigation strategies for this vulnerability primarily involve applying the upstream kernel patch that introduces proper error handling checks after virtio_gpu_fence_alloc calls. System administrators should ensure their Linux kernels are updated to versions where this fix is included, particularly in environments running virtual machines with GPU passthrough or virtio-gpu support enabled. For developers maintaining custom builds of the kernel, it is essential to implement defensive coding practices by verifying all pointer returns from memory allocation functions before use. Additionally, enabling Kernel Address Sanitizer (KASAN) during development and testing phases can help detect such null dereferences early in the software lifecycle, preventing them from reaching production environments where they could be exploited for denial of service attacks against virtualized infrastructure.