From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=100.103.45.18 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1794049252; b=S3sVYpZHWk6eaB2976fnEdoHeoI28EQiIrDI3Y+OQpBZ6Xpv95iFO8SpvGNQjQbtzrSU +2pmIqR2FOFMrxDDYVUzJwdZdXQpKE4b1krhZ9rXZnF2V1BS2Qbo/D1xO6cU+hzyp+PV9 OpvsEiE9sJlNhpnXWcvy0UV8i3lizjDgBlJ24X/wya/kiqiMozO3b6ZUSclLH8W8/DyU2 sxpHkSA73u9QFpBqT7RRtQ/29n7WejrXXapPnvU/aKVVaJLBgPc0Nxt1+TYF3hnBaotHr DduV95+YcQ1/Xhdkas7gJpG/TvS7GrGg7AbCEeasax17pHQAdhz3Qdprv06fmzaUFRw== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1794049252; h=Received:DKIM-Signature:From:To:Cc:Subject:Date:Message-ID:X-Mailer: MIME-Version:Content-Type:Content-Transfer-Encoding; bh=nB7nfcG/43CamqBDsQmkONWkznQFFP5uuY4oSeaP+Pc=; b=AvpTg3zm6v4CSKc2PqAd9AdXzwlhEiHOlitX+sxgdxXhN44luCItw+plK2AqAh2Rcx2S h8TWnSUyhQUix+X9DZiPZnGm6jRJuWKXV0vlSYGITYIXgyUqp1Hy0zoNHNpmTGAxIzXcA 1fIbQWRuZzPSUbQQvq8QcilrwAFCaLnBX7xHstcD6/UQLxA6sO763+FK76p7Os1DrqoQW UhISncomqMKeMyW6hrTK+UnMn4kXcGxZcou7QlSeWazBtDu/PuJGRgWbzoTZxFk78sS3/ 6XVdpif8xutRfusenMSLpeLtX8e1HIQjUn44mOmoyF10C9RPmAUe+lXPJ5HXN4BVQdA== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=Y3uIsDhF; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id BDAFA606A326 for ; Sat, 7 Nov 2026 11:00:51 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=Y3uIsDhF Received: by smtp.kernel.org (Postfix) with ESMTPSA id 38B9B1F0089F; Sat, 7 Nov 2026 11:00:51 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1794049251; bh=nB7nfcG/43CamqBDsQmkONWkznQFFP5uuY4oSeaP+Pc=; h=From:To:Cc:Subject:Date; b=Y3uIsDhFwHTwMGkxhvC3bsgQWrNjjs+sjgJjU1xiqt+k8GlitsZy+XLGXwQdzRfLM jrYTqe7hf1T0h38x9tvhBFyP9mf4CkD8khgqxxA9mp9ZW6JYnFBLncWD3eGAM5/Z39 a0ji9fc5gb9ndt5oON9aSECenjViavVhXCBkIo7MX+uW8NbCjefAVOaRnlNp8G23oV UKDxCON7P0m/V/OvgZci2Yvs5ynuKOZfLkoXNUrY7MTGD+0lMTJKEgqDdZK1lUYPVi F8PdugsHbOUFkeGGOjjuMsWWyDmgF8sQTBfX2h0q3t1FmLqjU934AkVLE4zY8SnLft Y0H6H4Pt00h9A== From: Sasha Levin To: tiwai@suse.de, farhad.alemi@berkeley.edu Cc: stable@vger.kernel.org Subject: FAILED: patch "[PATCH] ALSA: control: Fix UAF in snd_ctl_elem_add() on card disconnect" failed to apply to 5.15-stable tree Date: Sat, 7 Nov 2026 06:00:50 -0500 Message-ID: <20261107060049-failed-5.15-d4febca239be@kernel.org> X-Mailer: git-send-email 2.53.0 X-Mailing-List: stable@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit The patch below does not apply to the 5.15-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to . To reproduce the conflict and resubmit, you may use the following commands: git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.15.y git checkout FETCH_HEAD git cherry-pick -x d4febca239be3c91498762dd0535a87d4af1eabc # git commit -s git send-email --to '' --in-reply-to '20261107060049-failed-5.15-d4febca239be@kernel.org' --subject-prefix 'PATCH 5.15.y' 'HEAD^..' Thanks, Sasha ------------------ original commit in Linus's tree ------------------ >From d4febca239be3c91498762dd0535a87d4af1eabc Mon Sep 17 00:00:00 2001 From: Takashi Iwai Date: Tue, 29 Sep 2026 14:53:42 +0200 Subject: [PATCH] ALSA: control: Fix UAF in snd_ctl_elem_add() on card disconnect A use-after-free can be triggered via SNDRV_CTL_IOCTL_ELEM_ADD when a USB audio card is disconnected while an ELEM_ADD ioctl is in flight. The reproducer parks the ioctl thread inside copy_from_user() using userfaultfd, then tears down the USB device. Unlike every other ALSA control _user handler (ELEM_INFO, ELEM_READ, ELEM_WRITE, TLV_*), snd_ctl_elem_add_user() never calls snd_power_ref_and_wait(), so the parked thread holds no power reference. snd_card_disconnect() therefore cannot observe it via snd_power_sync_ref() and proceeds unimpeded: 1. card->shutdown is set to 1 2. device_del(&card->card_dev) drops the kobject reference on the parent USB interface device (card->dev = &intf->dev) 3. The USB core drops its own reference and calls device_release(), freeing the struct usb_interface, including the embedded struct device that card->dev points to When the userfaultfd is resolved and the thread resumes, snd_ctl_elem_add() acquires controls_rwsem without checking card->shutdown and calls __snd_ctl_add_replace(). Because the reproducer pre-registered the same control, the CTL_ADD_EXCLUSIVE path calls dev_err(card->dev, ...) on the freed USB interface: KASAN: slab-use-after-free Read in __dev_printk Add a card->shutdown guard immediately after acquiring controls_rwsem in snd_ctl_elem_add(). At that point card->shutdown is guaranteed to be stable: snd_card_disconnect() sets it before freeing the parent device, and it never transitions back to 0. A thread that acquired the lock before disconnect sees shutdown=0 and holds the write lock through the rest of the operation, preventing concurrent disconnect from proceeding past its own controls_rwsem-less shutdown=1 store (which happened earlier, outside the lock) from racing with dev_err(). Reported-by: Farhad Alemi Cc: stable@vger.kernel.org Signed-off-by: Takashi Iwai Link: https://patch.msgid.link/20260929125346.1478631-3-tiwai@suse.de --- sound/core/control.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/sound/core/control.c b/sound/core/control.c index 4199342d4ffe0..535ceba294acf 100644 --- a/sound/core/control.c +++ b/sound/core/control.c @@ -1802,6 +1802,8 @@ static int snd_ctl_elem_add(struct snd_ctl_file *file, alloc_size = compute_user_elem_size(private_size, count); guard(rwsem_write)(&card->controls_rwsem); + if (card->shutdown) + return -ENODEV; if (check_user_elem_overflow(card, alloc_size)) return -ENOMEM; -- 2.53.0