From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-14.3 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 4034AC47094 for ; Thu, 10 Jun 2021 15:21:46 +0000 (UTC) Received: from gabe.freedesktop.org (gabe.freedesktop.org [131.252.210.177]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 01B6361182 for ; Thu, 10 Jun 2021 15:21:45 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 01B6361182 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=gmail.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=dri-devel-bounces@lists.freedesktop.org Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id 6C8256ED72; Thu, 10 Jun 2021 15:21:45 +0000 (UTC) Received: from mail-pj1-x102b.google.com (mail-pj1-x102b.google.com [IPv6:2607:f8b0:4864:20::102b]) by gabe.freedesktop.org (Postfix) with ESMTPS id 787E76ED64 for ; Thu, 10 Jun 2021 15:21:44 +0000 (UTC) Received: by mail-pj1-x102b.google.com with SMTP id m13-20020a17090b068db02901656cc93a75so3936219pjz.3 for ; Thu, 10 Jun 2021 08:21:44 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=subject:to:references:from:message-id:date:user-agent:mime-version :in-reply-to:content-language:content-transfer-encoding; bh=FuMYH+W4A5O7+Tews5dUBZThHa9L7Mfi17lH81DY2zM=; b=geW08CQPQBOVBMMTrnm4QUFNszNlWY3MoOiwGTuxU4NxJ7MI2P5D3oCLIMfMw0dMy+ x+MAOJ9JGVdJiaP1cAH7u2dY8eX8FzNnaEPEresoL8Y0KlYO/JAWlw9i0Pap8ssR4A8h pXah6TYAeLM6CpQIP4weQ4x92R5zT/1f8OHYjrFFyL2CAJ6jpBTnuxhLsHs2o/UQCBvr LscT4VJWLKBGredrdp958uDKi4IuaIIuZrliAXNigqpz7BebZtMAOc2k1Uz8XzPE5JcG wrlGJe8bndU79Igoq2Yb2IcvMCqi1Nag+DNg47+6VQVynXTqVvEdK5F1KDX6wljdI0Td AnJQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:subject:to:references:from:message-id:date :user-agent:mime-version:in-reply-to:content-language :content-transfer-encoding; bh=FuMYH+W4A5O7+Tews5dUBZThHa9L7Mfi17lH81DY2zM=; b=GC6ErpgNd2F8HvKZ1MEr6CtRX0T1z7s9tnGIWpXIXqEGB3K2OSbTjXuAE0h1wWX7ei 6tmfeXIViXS3llXEOc7AIT1/CENZIspWadezbu83Z51/XPhdPor2WDJ1BYPvRFB0zccv myQqyWdarY7gEI5LfRqTGqkngi1GIDQo4wzJ4xh3V1Kn8WbQrNIyJEFKay5PshkbSPVy vScmV/iYjPGOhiet8XMLMQQR+aj1KO5CCANbwHOkcl0qW3aylk6yHNwFE2vtnfvLp0Y2 +IjXa9AWtK09gOOr538yiqpmXzILg8axsm4LZPWRpEfzofS3mvzoYGbUrLoxOvJn4XCr 4Zew== X-Gm-Message-State: AOAM533pUTSR5ZLBsmr0reNjUEh7bcT7ZMSfF1hx1JTl3Ugc2+Wm3BUv z8izyW8THp6zEm8MZLnNrF8= X-Google-Smtp-Source: ABdhPJwY3Ac4NGkGa69ARb226Snl9c/IgAMvA5T4R/MfkCVsafMp2WO5EMJAHpECCzDhwmOKZgu58w== X-Received: by 2002:a17:90a:1b8f:: with SMTP id w15mr3847687pjc.101.1623338504011; Thu, 10 Jun 2021 08:21:44 -0700 (PDT) Received: from [192.168.1.237] ([118.200.190.93]) by smtp.gmail.com with ESMTPSA id d92sm2920355pjk.38.2021.06.10.08.21.40 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 10 Jun 2021 08:21:43 -0700 (PDT) Subject: Re: [PATCH] drm: Lock pointer access in drm_master_release() To: maarten.lankhorst@linux.intel.com, mripard@kernel.org, tzimmermann@suse.de, airlied@linux.ie, dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org, skhan@linuxfoundation.org, gregkh@linuxfoundation.org, linux-kernel-mentees@lists.linuxfoundation.org, Dan Carpenter References: <20210609092119.173590-1-desmondcheongzx@gmail.com> From: Desmond Cheong Zhi Xi Message-ID: Date: Thu, 10 Jun 2021 23:21:39 +0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.8.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=windows-1252; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-BeenThere: dri-devel@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Direct Rendering Infrastructure - Development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: dri-devel-bounces@lists.freedesktop.org Sender: "dri-devel" On 10/6/21 6:10 pm, Daniel Vetter wrote: > On Wed, Jun 09, 2021 at 05:21:19PM +0800, Desmond Cheong Zhi Xi wrote: >> This patch eliminates the following smatch warning: >> drivers/gpu/drm/drm_auth.c:320 drm_master_release() warn: unlocked access 'master' (line 318) expected lock '&dev->master_mutex' >> >> The 'file_priv->master' field should be protected by the mutex lock to >> '&dev->master_mutex'. This is because other processes can concurrently >> modify this field and free the current 'file_priv->master' >> pointer. This could result in a use-after-free error when 'master' is >> dereferenced in subsequent function calls to >> 'drm_legacy_lock_master_cleanup()' or to 'drm_lease_revoke()'. >> >> An example of a scenario that would produce this error can be seen >> from a similar bug in 'drm_getunique()' that was reported by Syzbot: >> https://syzkaller.appspot.com/bug?id=148d2f1dfac64af52ffd27b661981a540724f803 >> >> In the Syzbot report, another process concurrently acquired the >> device's master mutex in 'drm_setmaster_ioctl()', then overwrote >> 'fpriv->master' in 'drm_new_set_master()'. The old value of >> 'fpriv->master' was subsequently freed before the mutex was unlocked. >> >> Reported-by: Dan Carpenter >> Signed-off-by: Desmond Cheong Zhi Xi > > Thanks a lot. I've done an audit of this code, and I found another > potential problem in drm_is_current_master. The callers from drm_auth.c > hold the dev->master_mutex, but all the external ones dont. I think we > need to split this into a _locked function for use within drm_auth.c, and > the exported one needs to grab the dev->master_mutex while it's checking > master status. Ofc there will still be races, those are ok, but right now > we run the risk of use-after free problems in drm_lease_owner. > > Are you up to do that fix too? > Hi Daniel, Thanks for the pointer, I'm definitely up for it! > I think the drm_lease.c code also needs an audit, there we'd need to make > sure that we hold hold either the lock or a full master reference to avoid > the use-after-free issues here. > I'd be happy to look into drm_lease.c as well. > Patch merged to drm-misc-fixes with cc: stable. > -Daniel > >> --- >> drivers/gpu/drm/drm_auth.c | 3 ++- >> 1 file changed, 2 insertions(+), 1 deletion(-) >> >> diff --git a/drivers/gpu/drm/drm_auth.c b/drivers/gpu/drm/drm_auth.c >> index f00e5abdbbf4..b59b26a71ad5 100644 >> --- a/drivers/gpu/drm/drm_auth.c >> +++ b/drivers/gpu/drm/drm_auth.c >> @@ -315,9 +315,10 @@ int drm_master_open(struct drm_file *file_priv) >> void drm_master_release(struct drm_file *file_priv) >> { >> struct drm_device *dev = file_priv->minor->dev; >> - struct drm_master *master = file_priv->master; >> + struct drm_master *master; >> >> mutex_lock(&dev->master_mutex); >> + master = file_priv->master; >> if (file_priv->magic) >> idr_remove(&file_priv->master->magic_map, file_priv->magic); >> >> -- >> 2.25.1 >> > From what I can see, there are other places in the kernel that could use the _locked version of drm_is_current_master as well, such as drm_mode_getfb in drm_framebuffer.c. I'll take a closer look, and if the changes make sense I'll prepare a patch series for them. Best wishes, Desmond