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 Received: from lists1p.gnu.org (lists1p.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 5669CC982FA for ; Tue, 22 Sep 2026 15:11:14 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists1p.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1x9299-00013K-JN; Tue, 22 Sep 2026 11:11:03 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists1p.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1x9298-000135-Ho; Tue, 22 Sep 2026 11:11:02 -0400 Received: from kylie.crudebyte.com ([5.189.157.229]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1x9296-0000xp-V5; Tue, 22 Sep 2026 11:11:02 -0400 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=crudebyte.com; s=kylie; h=Content-Type:Content-Transfer-Encoding: MIME-Version:References:In-Reply-To:Message-ID:Date:Subject:Cc:To:From: Content-ID:Content-Description; bh=VS1pYh26Ucsso/Fh7CZSSGHyw504gytKGzzopyqGhM4=; b=buoX4O2GA6eG0V5/Jnfb8zz4XO eUC5G3nqX42ofAEzuBW25WaS5Fbcea0vwmNkcvKX8DdEPHRE2FwvAJrzL8wsZUBfDxbtbAm8D+G+m SIKNtl1Yv4bQeLnOfZGyEKQvWTn9CTPnhkj6O3Wu1FdsY9LFve8aohSZLxQFD79V77eEfYJTM2nWF jKBVKH7bHFYl4ia1K6mFgJZwObIFV+1NQafmMJOQbsBooy0aKnNx6E5prP+nLT9TygDdX6619mOZM 0Hkdw3CJRUjtScHPSlwNaQSiI9rYA3aWYKeSDIYFIEjGK4HOe+0qGitTWJDwaBMTocs51sBG1fjk+ rgaWYBdoOuq5GP8tXuaiFdpKTq0A4yICW5VpH12B291p6LF/xsnJ3/UwyOrzvYLvvu5xsaB0Rb1Ym OTgp6Dqp6pzquu4/gW8GD1ORcnj+zoaDNU3XRYi1Np/nWoXJrx4Mc4WRSx0X942dpZIFqJoPjO0Qe fGtzfyk6UaCtchriGq2fh6s8wuaHJ8RvKBa8S+8SRwYZuqFQLKTQ/uetT9grF+7yKuiiZG/b2Lzch uyw/edtNNe566ID3Hw6nHH1Q+vRwFOiwtFvUvMmTA7GACwHB8C+uoANEqby7SSWAvkFpISGBiy0WT HdN3kGAW1IhTo82s9NVmWPeHldM6K4td2w8agfNeM=; From: Christian Schoenebeck To: Greg Kurz , qemu-devel@nongnu.org, qemu-stable@nongnu.org Cc: Daniel =?UTF-8?B?UC4gQmVycmFuZ8Op?= Subject: Re: [PATCH] hw/9pfs: mutate FID path from main thread only (CVE-2026-93834) Date: Tue, 22 Sep 2026 17:10:58 +0200 Message-ID: <3717038.iIbC2pHGDl@weasel> In-Reply-To: References: <20260922081301.244e5524@bahia> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" Received-SPF: pass client-ip=5.189.157.229; envelope-from=qemu_oss@crudebyte.com; helo=kylie.crudebyte.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, SPF_HELO_PASS=-0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: qemu development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On Tuesday, 22 September 2026 14:30:53 CEST Daniel P. Berrang=C3=A9 wrote: > On Tue, Sep 22, 2026 at 08:13:01AM +0200, Greg Kurz wrote: > > On Mon, 21 Sep 2026 14:18:58 +0200 > >=20 > > Christian Schoenebeck wrote: > > > v9fs_co_open2() is the only code that mutates a FID path from a worker > > > thread: inside its v9fs_co_run_in_worker() block it frees fidp->path > > > and copies in the new path under the held FID path write lock. > > >=20 > > > Every other FID path mutation in the 9p codebase happens on the main > > > thread, so main thread readers (v9fs_walk(), v9fs_xattrwalk(), > > > v9fs_stat(), v9fs_co_name_to_path()) rely on the same (main) thread > > > atomicity and don't take the path read lock themselves on main thread. > > >=20 > > > Fix this by making the worker thread block in v9fs_co_open2() read-on= ly > > > with respect to the FID: render the new path into the local 'path' > > > variable only and copy it to fidp->path after the worker block return= ed > > > back to the main thread and still under the held write lock of the FI= D, > > > like every other FID path mutation does. > > >=20 > > > Fixes: 02cb7f3a25 ("hw/9pfs: Use read-write lock for protecting fid > > > path.") > >=20 > > Wow, it's a long standing issue ! ;-) > >=20 > > > Fixes: CVE-2026-93834 > >=20 > > Cannot find it... embargoed ? > >=20 > > > Reported-by: Milad Nasr > > > Suggested-by: Milad Nasr > > > Resolves: https://gitlab.com/qemu-project/qemu/-/work_items/4491 > >=20 > > Cannot find that either... >=20 > Initially confidential, so only visible to maintainers with acccounts > added to the gitlab project. Bugs should be made public when their > patch is posted for review, so I've turned off the confidential flag > now. Strange policies. I would have: =2D Added Greg (reviewer and previous 9p maintainer for years) to the repor= t=20 while it was still private. Instead I am the only one getting LLM generated= =20 security reports thrown at me. =2D Considering the severeness of the vulnerability, I would have waited fo= r the=20 patch been pushed through stable branches before making the full report=20 public, or at least until merged on git. /Christian