linux-kernel - [PATCH] drm/vgem: fix use-after-free when drm_gem_handle

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Message-Id: <20190226204726.92256-1-ebiggers@kernel.org>
Date:   Tue, 26 Feb 2019 12:47:26 -0800
From:   Eric Biggers <ebiggers@...nel.org>
To:     dri-devel@...ts.freedesktop.org, David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>
Cc:     Chris Wilson <chris@...is-wilson.co.uk>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>,
        linux-kernel@...r.kernel.org
Subject: [PATCH] drm/vgem: fix use-after-free when drm_gem_handle_create() fails

From: Eric Biggers <ebiggers@...gle.com>

If drm_gem_handle_create() fails in vgem_gem_create(), then the
drm_vgem_gem_object is freed twice: once when the reference is dropped
by drm_gem_object_put_unlocked(), and again by __vgem_gem_destroy().

This was hit by syzkaller using fault injection.

Fix it by skipping the second free.

Reported-by: syzbot+e73f2fb5ed5a5df36d33@...kaller.appspotmail.com
Fixes: 5ba6c9ff961a ("drm/vgem: Fix mmaping")
Cc: stable@...r.kernel.org
Signed-off-by: Eric Biggers <ebiggers@...gle.com>
---
 drivers/gpu/drm/vgem/vgem_drv.c | 8 +++-----
 1 file changed, 3 insertions(+), 5 deletions(-)

diff --git a/drivers/gpu/drm/vgem/vgem_drv.c b/drivers/gpu/drm/vgem/vgem_drv.c
index 5930facd6d2d8..70646d9da1596 100644
--- a/drivers/gpu/drm/vgem/vgem_drv.c
+++ b/drivers/gpu/drm/vgem/vgem_drv.c
@@ -189,15 +189,13 @@ static struct drm_gem_object *vgem_gem_create(struct drm_device *dev,
 		return ERR_CAST(obj);
 
 	ret = drm_gem_handle_create(file, &obj->base, handle);
+
 	drm_gem_object_put_unlocked(&obj->base);
+
 	if (ret)
-		goto err;
+		return ERR_PTR(ret);
 
 	return &obj->base;
-
-err:
-	__vgem_gem_destroy(obj);
-	return ERR_PTR(ret);
 }
 
 static int vgem_gem_dumb_create(struct drm_file *file, struct drm_device *dev,
-- 
2.21.0.rc2.261.ga7da99ff1b-goog