linux-kernel - [PATCH] drm/i915/gvt: Fix use-after-free in intel_vgpu_create

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Date:   Tue, 6 Aug 2019 21:20:33 -0500
From:   "Gustavo A. R. Silva" <gustavo@...eddedor.com>
To:     Zhenyu Wang <zhenyuw@...ux.intel.com>,
        Zhi Wang <zhi.a.wang@...el.com>,
        Jani Nikula <jani.nikula@...ux.intel.com>,
        Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
        Rodrigo Vivi <rodrigo.vivi@...el.com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Xiong Zhang <xiong.y.zhang@...el.com>
Cc:     intel-gvt-dev@...ts.freedesktop.org,
        intel-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org,
        "Gustavo A. R. Silva" <gustavo@...eddedor.com>
Subject: [PATCH] drm/i915/gvt: Fix use-after-free in
 intel_vgpu_create_workload

kmem_cache_free() frees *workload*, hence there is a use-after-free bug
when calling function gvt_vgpu_err().

Fix this by storing the value of workload->wa_ctx.indirect_ctx.guest_gma
and workload->wa_ctx.per_ctx.guest_gma into automatic variable
guest_gma before freeing *workload*, for its further use.

Addresses-Coverity-ID: 1452235 ("Read from pointer after free")
Fixes: 2089a76ade90 ("drm/i915/gvt: Checking workload's gma earlier")
Signed-off-by: Gustavo A. R. Silva <gustavo@...eddedor.com>
---
 drivers/gpu/drm/i915/gvt/scheduler.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/i915/gvt/scheduler.c b/drivers/gpu/drm/i915/gvt/scheduler.c
index 32ae6b5b7e16..c8cdb4a309f6 100644
--- a/drivers/gpu/drm/i915/gvt/scheduler.c
+++ b/drivers/gpu/drm/i915/gvt/scheduler.c
@@ -1525,9 +1525,11 @@ intel_vgpu_create_workload(struct intel_vgpu *vgpu, int ring_id,
 			if (!intel_gvt_ggtt_validate_range(vgpu,
 				workload->wa_ctx.indirect_ctx.guest_gma,
 				workload->wa_ctx.indirect_ctx.size)) {
+				unsigned long guest_gma =
+				       workload->wa_ctx.indirect_ctx.guest_gma;
 				kmem_cache_free(s->workloads, workload);
 				gvt_vgpu_err("invalid wa_ctx at: 0x%lx\n",
-				    workload->wa_ctx.indirect_ctx.guest_gma);
+					     guest_gma);
 				return ERR_PTR(-EINVAL);
 			}
 		}
@@ -1539,9 +1541,11 @@ intel_vgpu_create_workload(struct intel_vgpu *vgpu, int ring_id,
 			if (!intel_gvt_ggtt_validate_range(vgpu,
 				workload->wa_ctx.per_ctx.guest_gma,
 				CACHELINE_BYTES)) {
+				unsigned long guest_gma =
+					workload->wa_ctx.per_ctx.guest_gma;
 				kmem_cache_free(s->workloads, workload);
 				gvt_vgpu_err("invalid per_ctx at: 0x%lx\n",
-					workload->wa_ctx.per_ctx.guest_gma);
+					     guest_gma);
 				return ERR_PTR(-EINVAL);
 			}
 		}
-- 
2.22.0