| Message ID | 20180409131021.5132-1-stefanha@redhat.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Mon, Apr 09, 2018 at 09:10:21PM +0800, Stefan Hajnoczi wrote: > Commit d65026c6c62e7d9616c8ceb5a53b68bcdc050525 ("vhost: validate log > when IOTLB is enabled") introduced a regression. The logic was > originally: > > if (vq->iotlb) > return 1; > return A && B; > > After the patch the short-circuit logic for A was inverted: > > if (A || vq->iotlb) > return A; > return B; > > The correct logic is: > > if (!A || vq->iotlb) > return A; > return B; > > Reported-by: syzbot+65a84dde0214b0387ccd@syzkaller.appspotmail.com > Cc: Jason Wang <jasowang@redhat.com> > Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com> Acked-by: Michael S. Tsirkin <mst@redhat.com> > --- > drivers/vhost/vhost.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c > index 5320039671b7..f6af4210679a 100644 > --- a/drivers/vhost/vhost.c > +++ b/drivers/vhost/vhost.c > @@ -1246,7 +1246,7 @@ int vhost_vq_access_ok(struct vhost_virtqueue *vq) > { > int ret = vq_log_access_ok(vq, vq->log_base); > > - if (ret || vq->iotlb) > + if (!ret || vq->iotlb) > return ret; > > return vq_access_ok(vq, vq->num, vq->desc, vq->avail, vq->used); > -- > 2.14.3
On Mon, Apr 9, 2018 at 6:10 AM, Stefan Hajnoczi <stefanha@redhat.com> wrote: > @@ -1246,7 +1246,7 @@ int vhost_vq_access_ok(struct vhost_virtqueue *vq) > { > int ret = vq_log_access_ok(vq, vq->log_base); > > - if (ret || vq->iotlb) > + if (!ret || vq->iotlb) > return ret; That logic is still very non-obvious. This code already had one bug because of an odd illegible test sequence. Let's not keep the crazy code. Why not just do the *obvious* thing, and get rid of "ret" entirely, and make the damn thing return a boolean, and then just write it all as /* Caller should have vq mutex and device mutex */ bool vhost_vq_access_ok(struct vhost_virtqueue *vq) { if (!vq_log_access_ok(vq, vq->log_base)) return false; if (vq->iotlb || vq_access_ok(vq, vq->num, vq->desc, vq->avail, vq->used); } which makes the logic obvious: if vq_log_access_ok() fails, then then vhost_vq_access_ok() fails unconditionally. Otherwise, we need to have an iotlb, or a successful vq_access_ok() check. Doesn't that all make more sense, and avoid the insane "ret" value use that is really quite subtle? Linus
On Mon, Apr 09, 2018 at 09:52:13AM -0700, Linus Torvalds wrote: > On Mon, Apr 9, 2018 at 6:10 AM, Stefan Hajnoczi <stefanha@redhat.com> wrote: > > @@ -1246,7 +1246,7 @@ int vhost_vq_access_ok(struct vhost_virtqueue *vq) > > { > > int ret = vq_log_access_ok(vq, vq->log_base); > > > > - if (ret || vq->iotlb) > > + if (!ret || vq->iotlb) > > return ret; > > That logic is still very non-obvious. > > This code already had one bug because of an odd illegible test > sequence. Let's not keep the crazy code. > > Why not just do the *obvious* thing, and get rid of "ret" entirely, > and make the damn thing return a boolean, and then just write it all > as > > /* Caller should have vq mutex and device mutex */ > bool vhost_vq_access_ok(struct vhost_virtqueue *vq) > { > if (!vq_log_access_ok(vq, vq->log_base)) > return false; > > if (vq->iotlb || vq_access_ok(vq, vq->num, vq->desc, > vq->avail, vq->used); > } > > which makes the logic obvious: if vq_log_access_ok() fails, then then > vhost_vq_access_ok() fails unconditionally. > > Otherwise, we need to have an iotlb, or a successful vq_access_ok() check. > > Doesn't that all make more sense, and avoid the insane "ret" value use > that is really quite subtle? > > Linus I agree it's cleaner. Stefan, I reposted your patch on netdev (since the breakage got applied there too). Would you like to self-nak it and post v2? Pls remember to CC netdev.
diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c index 5320039671b7..f6af4210679a 100644 --- a/drivers/vhost/vhost.c +++ b/drivers/vhost/vhost.c @@ -1246,7 +1246,7 @@ int vhost_vq_access_ok(struct vhost_virtqueue *vq) { int ret = vq_log_access_ok(vq, vq->log_base); - if (ret || vq->iotlb) + if (!ret || vq->iotlb) return ret; return vq_access_ok(vq, vq->num, vq->desc, vq->avail, vq->used);
Commit d65026c6c62e7d9616c8ceb5a53b68bcdc050525 ("vhost: validate log when IOTLB is enabled") introduced a regression. The logic was originally: if (vq->iotlb) return 1; return A && B; After the patch the short-circuit logic for A was inverted: if (A || vq->iotlb) return A; return B; The correct logic is: if (!A || vq->iotlb) return A; return B; Reported-by: syzbot+65a84dde0214b0387ccd@syzkaller.appspotmail.com Cc: Jason Wang <jasowang@redhat.com> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com> --- drivers/vhost/vhost.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)