On 9/9/26 12:11, Peiyang He wrote:
> 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:0000000000000000
> CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00007f24c3759000 CR3: 0000000048d19000 CR4: 0000000000350ef0
> ----------------
> Code disassembly (best guess):
> 0: 85 ed test %ebp,%ebp
> 2: 0f 85 21 09 00 00 jne 0x929
> 8: e8 05 5a c9 fb call 0xfbc95a12
> d: 48 8b 44 24 10 mov 0x10(%rsp),%rax
> 12: 48 8d b8 90 00 00 00 lea 0x90(%rax),%rdi
> 19: 48 b8 00 00 00 00 00 movabs $0xdffffc0000000000,%rax
> 20: fc ff df
> 23: 48 89 fa mov %rdi,%rdx
> 26: 48 c1 ea 03 shr $0x3,%rdx
> * 2a: 80 3c 02 00 cmpb $0x0,(%rdx,%rax,1) <-- trapping
> instruction
> 2e: 0f 85 9a 0d 00 00 jne 0xdce
> 34: 48 8b 44 24 10 mov 0x10(%rsp),%rax
> 39: 4c 89 b0 90 00 00 00 mov %r14,0x90(%rax)
>
> Fix by checking virtio_gpu_fence_alloc() in virtio_gpu_init_submit() and
> returning -ENOMEM before any later code can dereference the NULL fence.
>
> Fixes: 70d1ace56db6 ("drm/virtio: Conditionally allocate virtio_gpu_fence")
> Cc: [email protected]
> Signed-off-by: Peiyang He <[email protected]>
> Assisted-by: Codex:gpt-5.5
> ---
> drivers/gpu/drm/virtio/virtgpu_submit.c | 7 +++++--
> 1 file changed, 5 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/virtio/virtgpu_submit.c
> b/drivers/gpu/drm/virtio/virtgpu_submit.c
> index 32cb1e4aa425..857ed5c5f2a8 100644
> --- a/drivers/gpu/drm/virtio/virtgpu_submit.c
> +++ b/drivers/gpu/drm/virtio/virtgpu_submit.c
> @@ -389,10 +389,13 @@ static int virtio_gpu_init_submit(struct
> virtio_gpu_submit *submit,
> if ((exbuf->flags & VIRTGPU_EXECBUF_FENCE_FD_OUT) ||
> exbuf->num_out_syncobjs ||
> exbuf->num_bo_handles ||
> - drm_fence_event)
> + drm_fence_event) {
> out_fence = virtio_gpu_fence_alloc(vgdev, fence_ctx, ring_idx);
> - else
> + if (!out_fence)
> + return -ENOMEM;
> + } else {
> out_fence = NULL;
> + }
>
> if (drm_fence_event) {
> err = virtio_gpu_fence_event_create(dev, file, out_fence,
> ring_idx);
Applied to misc-fixes, thanks!
--
Best regards,
Dmitry
