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[PATCH] drm/virtio: fix NULL pointer dereference on fence allocation failure

Peiyang He posted 1 patch 2 weeks, 2 days ago 
drivers/gpu/drm/virtio/virtgpu_submit.c | 7 +++++--
1 file changed, 5 insertions(+), 2 deletions(-)
[PATCH] drm/virtio: fix NULL pointer dereference on fence allocation failure
Posted by Peiyang He 2 weeks, 2 days ago 
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: stable@vger.kernel.org
Signed-off-by: Peiyang He <peiyang_he@smail.nju.edu.cn>
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);
-- 
2.43.0
Re: [PATCH] drm/virtio: fix NULL pointer dereference on fence allocation failure
Posted by Dmitry Osipenko 5 days ago 
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: stable@vger.kernel.org
> Signed-off-by: Peiyang He <peiyang_he@smail.nju.edu.cn>
> 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

Patchew 2.1-devel-ea86937

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