linux-kernel - Re: [PATCH] KVM: x86/xen: Fix eventfd error handling in kvm_xen_eventfd

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Date:   Fri, 28 Oct 2022 12:47:17 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Eiichi Tsukata <eiichi.tsukata@...anix.com>, seanjc@...gle.com,
        tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
        dave.hansen@...ux.intel.com, x86@...nel.org, hpa@...or.com,
        kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        ankur.a.arora@...cle.com, dwmw@...zon.co.uk,
        joao.m.martins@...cle.com
Cc:     syzbot+6f0c896c5a9449a10ded@...kaller.appspotmail.com
Subject: Re: [PATCH] KVM: x86/xen: Fix eventfd error handling in
 kvm_xen_eventfd_assign()

On 10/28/22 11:26, Eiichi Tsukata wrote:
> Should not call eventfd_ctx_put() in case of error.
> 
> Fixes: 2fd6df2f2b47 ("KVM: x86/xen: intercept EVTCHNOP_send from guests")
> Reported-by: syzbot+6f0c896c5a9449a10ded@...kaller.appspotmail.com
> Signed-off-by: Eiichi Tsukata <eiichi.tsukata@...anix.com>
> ---
>   arch/x86/kvm/xen.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kvm/xen.c b/arch/x86/kvm/xen.c
> index 93c628d3e3a9..a357994982c6 100644
> --- a/arch/x86/kvm/xen.c
> +++ b/arch/x86/kvm/xen.c
> @@ -1716,7 +1716,7 @@ static int kvm_xen_eventfd_assign(struct kvm *kvm,
>   	if (ret == -ENOSPC)
>   		ret = -EEXIST;
>   out:
> -	if (eventfd)
> +	if (eventfd && !IS_ERR(eventfd))
>   		eventfd_ctx_put(eventfd);
>   	kfree(evtchnfd);
>   	return ret;

Slightly more verbose, but cleaner:

diff --git a/arch/x86/kvm/xen.c b/arch/x86/kvm/xen.c
index 6714bbdbedf3..2dae413bd62a 100644
--- a/arch/x86/kvm/xen.c
+++ b/arch/x86/kvm/xen.c
@@ -1666,18 +1666,18 @@ static int kvm_xen_eventfd_assign(struct kvm *kvm,
  	case EVTCHNSTAT_ipi:
  		/* IPI  must map back to the same port# */
  		if (data->u.evtchn.deliver.port.port != data->u.evtchn.send_port)
-			goto out; /* -EINVAL */
+			goto out_noeventfd; /* -EINVAL */
  		break;
  
  	case EVTCHNSTAT_interdomain:
  		if (data->u.evtchn.deliver.port.port) {
  			if (data->u.evtchn.deliver.port.port >= max_evtchn_port(kvm))
-				goto out; /* -EINVAL */
+				goto out_noeventfd; /* -EINVAL */
  		} else {
  			eventfd = eventfd_ctx_fdget(data->u.evtchn.deliver.eventfd.fd);
  			if (IS_ERR(eventfd)) {
  				ret = PTR_ERR(eventfd);
-				goto out;
+				goto out_noeventfd;
  			}
  		}
  		break;
@@ -1717,6 +1717,7 @@ static int kvm_xen_eventfd_assign(struct kvm *kvm,
  out:
	if (eventfd)
  		eventfd_ctx_put(eventfd);
+out_noeventfd:
  	kfree(evtchnfd);
  	return ret;
  }

Only the last goto has to be changed in order to fix the bug, the
others are only needed to respect the LIFO order of the unwinding
labels.

Paolo