From a254fe579062a9eaf97f2b81474c19b4b46ddc85 Mon Sep 17 00:00:00 2001
From: Alex Williamson <alex.williamson@redhat.com>
Date: Fri, 10 Apr 2015 16:33:56 +0200
Subject: [PATCH 04/14] vfio: Fix overrun after readlink() fills buffer
 completely

Message-id: <20150410163356.15324.47617.stgit@gimli.home>
Patchwork-id: 64786
O-Subject: [RHEL7.2 qemu-kvm PATCH 4/8] vfio: Fix overrun after readlink() fills buffer completely
Bugzilla: 1210504
RH-Acked-by: Thomas Huth <thuth@redhat.com>
RH-Acked-by: Laszlo Ersek <lersek@redhat.com>
RH-Acked-by: Bandan Das <bsd@redhat.com>

From: Markus Armbruster <armbru@redhat.com>

Upstream: 13665a2d2f675341e73618fcd7f9d36b6c68b509

readlink() returns the number of bytes written to the buffer, and it
doesn't write a terminating null byte.  vfio_init() writes it itself.
Overruns the buffer when readlink() filled it completely.

Fix by treating readlink() filling the buffer completely as error,
like we do in pci-assign.c's assign_failed_examine().

Spotted by Coverity.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
Signed-off-by: Miroslav Rezanina <mrezanin@redhat.com>
---
 hw/misc/vfio.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/hw/misc/vfio.c b/hw/misc/vfio.c
index 57bc974..81e6594 100644
--- a/hw/misc/vfio.c
+++ b/hw/misc/vfio.c
@@ -3767,10 +3767,10 @@ static int vfio_initfn(PCIDevice *pdev)
 
     strncat(path, "iommu_group", sizeof(path) - strlen(path) - 1);
 
-    len = readlink(path, iommu_group_path, PATH_MAX);
-    if (len <= 0) {
+    len = readlink(path, iommu_group_path, sizeof(path));
+    if (len <= 0 || len >= sizeof(path)) {
         error_report("vfio: error no iommu_group for device");
-        return -errno;
+        return len < 0 ? -errno : ENAMETOOLONG;
     }
 
     iommu_group_path[len] = 0;
-- 
1.8.3.1