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 4673E4DDB35; Thu, 15 Oct 2026 16:25:03 +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=1792081515; cv=none; b=tHnE275FQt/KKuwUNDnBsbSIeGlipxTbRCVL/b6niLMyRNbW4yiCpB9d014YROoTcWdZsDNdqHHMG8YzkVv2kzgPXMi2rTAHdz9qxZbybvgWZHze2+LRdnH14hhUsLshr2UaJdauNIVUaCL829ylaW/CzMWSy25zJ3H9aqh9cLE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1792081515; c=relaxed/simple; bh=NJRLI3ehmSEpgTBEls8bsaM5nLIbgZNPc2143Iy49vQ=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=Ct0RiLivf0lWTw862h6wFJR331faguyfUbmA2/9gROvmXfXJ8bUJtZmP+GdS4x5erpR1Z1KvTVoZ8gBWbQ9OwyZXrEsQYZwEphL/fa2sAA9esumTrQt7zPKL94JtJWLu1DfI7ghR/2HyJgGSY/e6FUbxw+rmyRDrWmuCFuSWWK8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=Sg2OSTVN; 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="Sg2OSTVN" Received: by smtp.kernel.org (Postfix) with ESMTPSA id BFA831F000C4; Thu, 15 Oct 2026 16:25:02 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1792081502; bh=YmDX9bQ+H2eYCS0s9rsjukTcn3P4o2IORKpy2mY2a5E=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=Sg2OSTVN9N+cfwkBXHnBSUyCX6m3t+q3mGjXbWXCN73V+4di6lKBWq3iudwFsXM/0 dmVOw2kT97WWWxXO7/p84cx1pmX+1yA4zpgdbGoWbpkPM6Acn8u1r/eByBlTyccU99 dcahZGM4RwAbjl1k1vpPdDZ2vWOrFlX0o/Dcyxk0XoT31ER7eKEdbNIuSDsHeWd7ax r655PI3EGwDLUA1W3JtIt2/OmpWj2ZWweWLYhadOB57vVcucSNMKtQGtVsIJlomK/C zFnZjhXjI9YiFklzcvdMiEVL1BJZJCIJlZ4KeiaTJGvn21e3tf3BCQ78bJBtsIGdsH fqwGNhY4S2weA== Date: Thu, 15 Oct 2026 09:25:02 -0700 From: Kees Cook To: cve@kernel.org, linux-kernel@vger.kernel.org Cc: linux-cve-announce@vger.kernel.org, Greg Kroah-Hartman , Oleg Nesterov , Jinjie Ruan Subject: Re: CVE-2026-89603: entry: Fix seccomp bypass after ptrace with TSYNC Message-ID: <20261015162119.1a1e0d-kees@kernel.org> References: <2026091133-CVE-2026-89603-dad5@gregkh> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <2026091133-CVE-2026-89603-dad5@gregkh> On Fri, Sep 11, 2026 at 09:44:52PM +0200, Greg Kroah-Hartman wrote: > This race condition could allow an unprivileged process to execute > a prohibited system call (e.g., execve) that the newly installed filter > was intended to block, especially since the tracer might have modified > the system call number during the ptrace stop. I'm disputing this one: please reject CVE-2026-89603. The fix is a fine consistency change, but the flaw gave neither the tracer nor the tracee anything they didn't already have. The missed check only affects a thread's first filter. Once a thread has any filter, seccomp_run_filters() loads the current filter list when it runs, so a filter synced during the ptrace stop applies anyway. So the thread entered the syscall with no filter at all, and stopped under a tracer that controlled it. That tracer could already have made it run any syscall before the filter existed, or simply refused its seccomp() call. No syscall gets past a filter that was in place when the syscall started. The same window exists without ptrace: TSYNC can land just after syscall entry reads the work flags, and the syscall in flight runs unfiltered. TSYNC has never applied to a syscall a thread has already entered, only to its next one. Sorry I missed this when the CVE originally went out! Thank you to Oleg for calling this to my attention on the original patch's thread: https://lore.kernel.org/all/as9Jqi5BvSZWfxj8@redhat.com/ :) -Kees -- Kees Cook