From 9cf75f15324ca15f013d3dc6a95bb5066a58d375 Mon Sep 17 00:00:00 2001
From: Alex Williamson <alex.williamson@redhat.com>
Date: Mon, 3 Dec 2018 21:53:40 +0100
Subject: [PATCH 22/34] vfio/pci: Handle subsystem realpath() returning NULL

RH-Author: Alex Williamson <alex.williamson@redhat.com>
Message-id: <154387402054.26945.6430332743475303163.stgit@gimli.home>
Patchwork-id: 83231
O-Subject: [RHEL-7.7 qemu-kvm-rhev PATCH 5/7] vfio/pci: Handle subsystem realpath() returning NULL
Bugzilla: 1619778
RH-Acked-by: Peter Xu <peterx@redhat.com>
RH-Acked-by: Cornelia Huck <cohuck@redhat.com>
RH-Acked-by: Auger Eric <eric.auger@redhat.com>
RH-Acked-by: David Hildenbrand <david@redhat.com>

Bugzilla: 1619778

Fix error reported by Coverity where realpath can return NULL,
resulting in a segfault in strcmp().  This should never happen given
that we're working through regularly structured sysfs paths, but
trivial enough to easily avoid.

Fixes: 238e91728503 ("vfio/ccw/pci: Allow devices to opt-in for ballooning")
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
(cherry picked from commit a1c0f886496cfb4c336f8eb4155ed424567d653e)
Signed-off-by: Miroslav Rezanina <mrezanin@redhat.com>
---
 hw/vfio/pci.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/hw/vfio/pci.c b/hw/vfio/pci.c
index 3bc7636..ba3a393 100644
--- a/hw/vfio/pci.c
+++ b/hw/vfio/pci.c
@@ -2889,7 +2889,7 @@ static void vfio_realize(PCIDevice *pdev, Error **errp)
     tmp = g_strdup_printf("%s/subsystem", vdev->vbasedev.sysfsdev);
     subsys = realpath(tmp, NULL);
     g_free(tmp);
-    is_mdev = (strcmp(subsys, "/sys/bus/mdev") == 0);
+    is_mdev = subsys && (strcmp(subsys, "/sys/bus/mdev") == 0);
     free(subsys);
 
     trace_vfio_mdev(vdev->vbasedev.name, is_mdev);
-- 
1.8.3.1