From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id CDC1B3CB56B; Fri, 28 Aug 2026 08:51:41 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787907103; cv=none; b=LhgLw2MrLY09xjRo7YpTAfJhybxPALyzO3/ANMzkZU1mk1D4Jb8NiH3tyrOzdBE5on1TLFJh2BFiosWtJKCnMgH4IJBizdQNp+LMaKLzoUT50YeVHdiIKJiVDRFcFHzOvFTzM95QtuWrjBdXYQbStqnJ0iT/oyzcVZIrXEQFY78= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787907103; c=relaxed/simple; bh=Lehy00NdNljvDsHtHs9Ikhbdp0KCBAIDSAWxSxpM5Qc=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version:Content-Type; b=oHVVg9Ug5JgQaKEp6i/I4VFOaiZrpSqyQs81l/BTStxAnKq7SHU1Z45M54b/hvgdGSSUOHjYe45hqDOY05Gkx1TwBG31R7fi8Otvv64JiQEqlIQYysZuzUY0qSYfCVYh4dXBVL2S7touz1+0Kl1k7lDI06ls8ILThwl/5w6Lp/U= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=MwwoebXP; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="MwwoebXP" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 1DDB21F000E9; Fri, 28 Aug 2026 08:51:37 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1787907101; bh=iHBSUDDx1WbolXW0Nyh2IRj9cxuhb4M6H5r9hbv6v5w=; h=From:To:Cc:Subject:Date; b=MwwoebXPHKhkZn8W5TgPtCIHt2/bh0gn5bc3Op2iQ31YgzRxFScemnTxhXARslqi1 Yr6FVrT05g5hYx0UTnd8lheht+h9oqNXjqp1uFdgM5hBslha1xIAi3O/pfSCvwaAZG 13tIaTynKi1BrzAbc27OhQ01GK/rWqjFrEHtfJOgUtvDo/bTwLSA8PsZNf0vBlA1JQ lDHEo+YlF66FWIZ0wAMlDVeggU+Fbbvv/ddBithXCM83xLYAjMwytdgVZWB3MgjNtj bM1XyS4iXqTwQB7FsXYefGA4qA1uSKbJlym1Gp+tgtLZGCbJ66dn31s4GB6/ybmfwd c4NC5D8Hafz6g== From: "Jiri Slaby (SUSE)" To: devel@lists.crash-utility.osci.io Cc: "Jiri Slaby (SUSE)" , Gemini , =?UTF-8?q?Christian=20K=C3=B6nig?= , Tvrtko Ursulin , Dave Airlie , Gerd Hoffmann , Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , David Airlie , Simona Vetter , stable@vger.kernel.org, virtualization@lists.linux.dev, spice-devel@lists.freedesktop.org, dri-devel@lists.freedesktop.org Subject: [PATCH v2] drm/qxl: fix use-after-free and NULL pointer deref Date: Fri, 28 Aug 2026 10:51:36 +0200 Message-ID: <20260828085136.128561-1-jirislaby@kernel.org> X-Mailer: git-send-email 2.55.0 Precedence: bulk X-Mailing-List: virtualization@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit When allocating a `qxl_release` structure with `kmalloc()`, the underlying memory contained uninitialized garbage. Specifically, `release->base.flags` (part of the embedded `dma_fence`) was not cleared. This garbage in `base.flags` caused helper functions such as `dma_fence_was_initialized()` to return true even for releases where the fence was never actually initialized (e.g. via `dma_fence_init()`). Consequently, during release cleanup in `qxl_release_free()`, the driver attempted to put/free an uninitialized `dma_fence`, leading to refcount underflows (`refcount_t: underflow; use-after-free`) and subsequent NULL pointer dereferences in `dma_fence_signal_timestamp_locked()`. Fix this by switching from `kmalloc()` to `kzalloc_obj()` in `qxl_release_alloc()`, ensuring all fields (including embedded fence flags) are properly zero-initialized upon allocation, and remove redundant explicit zero-initializations. The dumps in question: refcount_t: underflow; use-after-free. WARNING: lib/refcount.c:28 at refcount_warn_saturate+0x59/0x90, CPU#0: kworker/0:0/1534 Modules linked in: af_packet nft_fib_inet ... CPU: 0 UID: 0 PID: 1534 Comm: kworker/0:0 Not tainted 7.1.3-1-default #1 PREEMPT(full) openSUSE Tumbleweed b041a6527f6e58424f4cd3de0fade8d408b378fd ... RIP: 0010:refcount_warn_saturate+0x59/0x90 ... Call Trace: qxl_release_free+0xee/0xf0 [qxl d93e9381353e619799d56790f5f8dda6cce491f6] qxl_garbage_collect+0xd1/0x1b0 [qxl d93e9381353e619799d56790f5f8dda6cce491f6] process_one_work+0x19e/0x3a0 ... And then of course: BUG: kernel NULL pointer dereference, address: 0000000000000028 ... RIP: 0010:dma_fence_signal_timestamp_locked+0x32/0x120 Signed-off-by: Jiri Slaby (SUSE) Assisted-by: Gemini # only commit log Fixes: 2bcbc706dfa0 ("dma-buf: add dma_fence_was_initialized function v2") Closes: https://bugzilla.suse.com/show_bug.cgi?id=1271081 Cc: Christian König Cc: Tvrtko Ursulin Cc: Dave Airlie Cc: Gerd Hoffmann Cc: Maarten Lankhorst Cc: Maxime Ripard Cc: Thomas Zimmermann Cc: David Airlie Cc: Simona Vetter Cc: stable@vger.kernel.org --- Cc: virtualization@lists.linux.dev Cc: spice-devel@lists.freedesktop.org Cc: dri-devel@lists.freedesktop.org [v2] use kzalloc_obj() instead of bare kzalloc() --- drivers/gpu/drm/qxl/qxl_release.c | 6 +----- 1 file changed, 1 insertion(+), 5 deletions(-) diff --git a/drivers/gpu/drm/qxl/qxl_release.c b/drivers/gpu/drm/qxl/qxl_release.c index 06979d0e8a9f..07dc6eafe6f7 100644 --- a/drivers/gpu/drm/qxl/qxl_release.c +++ b/drivers/gpu/drm/qxl/qxl_release.c @@ -89,17 +89,13 @@ qxl_release_alloc(struct qxl_device *qdev, int type, { struct qxl_release *release; int handle; - size_t size = sizeof(*release); - release = kmalloc(size, GFP_KERNEL); + release = kzalloc_obj(*release); if (!release) { DRM_ERROR("Out of memory\n"); return -ENOMEM; } - release->base.ops = NULL; release->type = type; - release->release_offset = 0; - release->surface_release_id = 0; INIT_LIST_HEAD(&release->bos); idr_preload(GFP_KERNEL); -- 2.55.0