Subject: Re: [PATCH] vhost-vdpa: fix use-after-free in _compat_vdpa_reset

From: "Michael S. Tsirkin" <[email-masked]>
Date: Thu, 26 Oct 2023 01:26:10 -0400

On Wed, Oct 25, 2023 at 04:13:14PM -0700, Si-Wei Liu wrote:
> When the vhost-vdpa device is being closed, vhost_vdpa_cleanup() doesn't
> clean up the vqs pointer after free. This could lead to use-after-tree
> when _compat_vdpa_reset() tries to access the vqs that are freed already.
> Fix is to set vqs pointer to NULL at the end of vhost_vdpa_cleanup()
> after getting freed, which is guarded by atomic opened state.
> 
>   BUG: unable to handle page fault for address: 00000001005b4af4
>   #PF: supervisor read access in kernel mode
>   #PF: error_code(0x0000) - not-present page
>   PGD 16a80a067 P4D 0
>   Oops: 0000 [#1] PREEMPT SMP NOPTI
>   CPU: 4 PID: 40387 Comm: qemu-kvm Not tainted 6.6.0-rc7+ #3
>   Hardware name: Dell Inc. PowerEdge R750/0PJ80M, BIOS 1.8.2 09/14/2022
>   RIP: 0010:_compat_vdpa_reset.isra.0+0x27/0xb0 [vhost_vdpa]
>   Code: 90 90 90 0f 1f 44 00 00 41 55 4c 8d ae 08 03 00 00 41 54 55 48
>   89 f5 53 4c 8b a6 00 03 00 00 48 85 ff 74 49 48 8b 07 4c 89 ef <48> 8b
>   80 88 45 00 00 48 c1 e8 08 48 83 f0 01 89 c3 e8 73 5e 9b dc
>   RSP: 0018:ff73a85762073ba0 EFLAGS: 00010286
>   RAX: 00000001005b056c RBX: ff32b13ca6994c68 RCX: 0000000000000002
>   RDX: 0000000000000001 RSI: ff32b13c07559000 RDI: ff32b13c07559308
>   RBP: ff32b13c07559000 R08: 0000000000000000 R09: ff32b12ca497c0f0
>   R10: ff73a85762073c58 R11: 0000000c106f9de3 R12: ff32b12c95b1d050
>   R13: ff32b13c07559308 R14: ff32b12d0ddc5100 R15: 0000000000008002
>   FS:  00007fec5b8cbf80(0000) GS:ff32b13bbfc80000(0000)
>   knlGS:0000000000000000
>   CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>   CR2: 00000001005b4af4 CR3: 000000015644a003 CR4: 0000000000773ee0
>   PKRU: 55555554
>   Call Trace:
>    <TASK>
>    ? __die+0x20/0x70
>    ? page_fault_oops+0x76/0x170
>    ? exc_page_fault+0x65/0x150
>    ? asm_exc_page_fault+0x22/0x30
>    ? _compat_vdpa_reset.isra.0+0x27/0xb0 [vhost_vdpa]
>    vhost_vdpa_open+0x57/0x280 [vhost_vdpa]
>    ? __pfx_chrdev_open+0x10/0x10
>    chrdev_open+0xc6/0x260
>    ? __pfx_chrdev_open+0x10/0x10
>    do_dentry_open+0x16e/0x530
>    do_open+0x21c/0x400
>    path_openat+0x111/0x290
>    do_filp_open+0xb2/0x160
>    ? __check_object_size.part.0+0x5e/0x140
>    do_sys_openat2+0x96/0xd0
>    __x64_sys_openat+0x53/0xa0
>    do_syscall_64+0x59/0x90
>    ? syscall_exit_to_user_mode+0x22/0x40
>    ? do_syscall_64+0x69/0x90
>    ? syscall_exit_to_user_mode+0x22/0x40
>    ? do_syscall_64+0x69/0x90
>    ? do_syscall_64+0x69/0x90
>    ? syscall_exit_to_user_mode+0x22/0x40
>    ? do_syscall_64+0x69/0x90
>    ? exc_page_fault+0x65/0x150
>    entry_SYSCALL_64_after_hwframe+0x6e/0xd8
> 
> Fixes: 10cbf8dfaf93 ("vhost-vdpa: clean iotlb map during reset for older userspace")
> Fixes: ac7e98c73c05 ("vhost-vdpa: fix NULL pointer deref in _compat_vdpa_reset")

So these two are all in next correct?

I really do not like it how 10cbf8dfaf936e3ef1f5d7fdc6e9dada268ba6bb
introduced a regression and then apparently we keep fixing things up?

Can I squash these 3 commits?

> Reported-by: Lei Yang <[email-masked]>
> Closes: https://lore.kernel.org/all/CAPpAL=[email-masked]/
> Signed-off-by: Si-Wei Liu <[email-masked]>
> ---
>  drivers/vhost/vdpa.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/drivers/vhost/vdpa.c b/drivers/vhost/vdpa.c
> index 9a2343c45df0..30df5c58db73 100644
> --- a/drivers/vhost/vdpa.c
> +++ b/drivers/vhost/vdpa.c
> @@ -1355,6 +1355,7 @@ static void vhost_vdpa_cleanup(struct vhost_vdpa *v)
>  	vhost_vdpa_free_domain(v);
>  	vhost_dev_cleanup(&v->vdev);
>  	kfree(v->vdev.vqs);
> +	v->vdev.vqs = NULL;
>  }
>  
>  static int vhost_vdpa_open(struct inode *inode, struct file *filep)
> -- 
> 2.39.3