[src/trunk]: src/sys/dev/pci Fix use-after-free. If we're not polling, virtio...

[maxv <maxv%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/56d82dfde55a
branches:  trunk
changeset: 455780:56d82dfde55a
user:      maxv <maxv%NetBSD.org@localhost>
date:      Sat Apr 13 06:17:33 2019 +0000

description:
Fix use-after-free. If we're not polling, virtio_enqueue_commit() will send
the transaction, and it means 'xs' can be immediately freed. So, save the
value of xs_control beforehand.

Detected by KASAN, ok jdolecek@.

Fixes PR/54008
Reported-by: syzbot+6513c4afe66237d7207f%syzkaller.appspotmail.com@localhost

diffstat:

 sys/dev/pci/vioscsi.c |  8 +++++---
 1 files changed, 5 insertions(+), 3 deletions(-)

diffs (38 lines):

diff -r 2481d0207f6b -r 56d82dfde55a sys/dev/pci/vioscsi.c
--- a/sys/dev/pci/vioscsi.c     Sat Apr 13 03:15:25 2019 +0000
+++ b/sys/dev/pci/vioscsi.c     Sat Apr 13 06:17:33 2019 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: vioscsi.c,v 1.20 2018/06/10 14:59:23 jakllsch Exp $    */
+/*     $NetBSD: vioscsi.c,v 1.21 2019/04/13 06:17:33 maxv Exp $        */
 /*     $OpenBSD: vioscsi.c,v 1.3 2015/03/14 03:38:49 jsg Exp $ */
 
 /*
@@ -18,7 +18,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: vioscsi.c,v 1.20 2018/06/10 14:59:23 jakllsch Exp $");
+__KERNEL_RCSID(0, "$NetBSD: vioscsi.c,v 1.21 2019/04/13 06:17:33 maxv Exp $");
 
 #include <sys/param.h>
 #include <sys/systm.h>
@@ -270,6 +270,7 @@
        struct virtio_scsi_req_hdr *req;
        struct virtqueue *vq = &sc->sc_vqs[VIOSCSI_VQ_REQUEST];
        int slot, error;
+       bool dopoll;
 
        DPRINTF(("%s: enter\n", __func__));
 
@@ -418,9 +419,10 @@
             sizeof(struct virtio_scsi_res_hdr), 0);
        if (xs->xs_control & XS_CTL_DATA_IN)
                virtio_enqueue(vsc, vq, slot, vr->vr_data, 0);
+       dopoll = (xs->xs_control & XS_CTL_POLL) != 0;
        virtio_enqueue_commit(vsc, vq, slot, 1);
 
-       if ((xs->xs_control & XS_CTL_POLL) == 0)
+       if (!dopoll)
                return;
 
        DPRINTF(("%s: polling...\n", __func__));