linux-kernel - [PATCH] drm/i915/kvmgt: avoid dereferencing a potentially null info pointer

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Message-Id: <20170323122230.19064-1-colin.king@canonical.com>
Date:   Thu, 23 Mar 2017 12:22:30 +0000
From:   Colin King <colin.king@...onical.com>
To:     Zhenyu Wang <zhenyuw@...ux.intel.com>,
        Zhi Wang <zhi.a.wang@...el.com>,
        Daniel Vetter <daniel.vetter@...el.com>,
        Jani Nikula <jani.nikula@...ux.intel.com>,
        David Airlie <airlied@...ux.ie>,
        intel-gvt-dev@...ts.freedesktop.org,
        intel-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org
Cc:     kernel-janitors@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH] drm/i915/kvmgt: avoid dereferencing a potentially null info pointer

From: Colin Ian King <colin.king@...onical.com>

info is being checked to see if it is a null pointer, however, vpgu is
dereferencing info before this check, leading to a potential null
pointer dereference.  If info is null, then the error message being
printed by macro gvt_vgpu_err and this requires vpgu to exist. We can
use a null vpgu as the macro has a sanity check to see if vpgu is null,
so this is OK.

Detected with CoverityScan, CID#1420672 ("Dereference nefore null check")

Fixes: 695fbc08d80f ("drm/i915/gvt: replace the gvt_err with gvt_vgpu_err")
Signed-off-by: Colin Ian King <colin.king@...onical.com>
---
 drivers/gpu/drm/i915/gvt/kvmgt.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/i915/gvt/kvmgt.c b/drivers/gpu/drm/i915/gvt/kvmgt.c
index 1ea3eb270de8..f8619a772c44 100644
--- a/drivers/gpu/drm/i915/gvt/kvmgt.c
+++ b/drivers/gpu/drm/i915/gvt/kvmgt.c
@@ -1339,9 +1339,9 @@ static int kvmgt_guest_init(struct mdev_device *mdev)
 
 static bool kvmgt_guest_exit(struct kvmgt_guest_info *info)
 {
-	struct intel_vgpu *vgpu = info->vgpu;
-
 	if (!info) {
+		struct intel_vgpu *vgpu = NULL;
+
 		gvt_vgpu_err("kvmgt_guest_info invalid\n");
 		return false;
 	}
-- 
2.11.0