From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 C0D0E14386D; Sun, 23 Mar 2025 20:57:25 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1742763445; cv=none; b=MhgXyc+7rGXHNl9ad+CIMdlTEiSZkF9Z3lgkdGKDgIHcrPgYqBpt1VFwtTv5yc8bQ6FkTHJSgWgjIGQTV1HNyBPQa9s+tO4ytUOy2FadD2HpBtQgs0vAZx3xREVRPyAIiGGChVhtSuPfDqelHXp0qmvGaJ0TyvPboQZWxUzMqPo= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1742763445; c=relaxed/simple; bh=Ev4tSesxO91BpPfkFPCZ9nFl2zIVQfSRk1iXPRbGrk4=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=PzLWzOdMpb0SLjqBZywO8iE7+rMQm/hwy0TJstX69xe+2ds7+UQ+lyQ9boUI1chfa7tc8suvNZHelKPulz/NEWRQGEOuQ74Gu4/y3BlI5+G79QY6Ry0yOwgTbovz1JmMjUyDlmqA44BEejMHJR5VP+OFBL5RktzU2F4v4PQHWpM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=rlV7EjwB; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="rlV7EjwB" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 6DD5EC4CEE2; Sun, 23 Mar 2025 20:57:24 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1742763445; bh=Ev4tSesxO91BpPfkFPCZ9nFl2zIVQfSRk1iXPRbGrk4=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=rlV7EjwBKKUpVqqY81Jdzx/BLuN+HSH3HFPkoJbJ/b3TEGabUg49QUOXOdp9wVz9h hdHAJGl1026w3fAjAKFnohMe7K6tbdWrIjtMNOQCP4btG79dkcZODFqwri6HDrtLSR +mSe6Z8ApNBw8stpzev3TuuCbj0+mOTnNWnHgNaeoyfpoLDExbYct7Y/dp2Bi21a4I /nyodGh8MR/x52VPoAACsUFO7XAbXMQ7YY6P/tI9TutSXSi3kn5NM111k2RBDS4zR4 PsBbMNsEJeKD56EXCncyYguBhi13hvDBzfKdNc456lAWSgfD1Ht4uXH1ZiUEVtWbjD KmuXIvCkkVlAQ== Date: Sun, 23 Mar 2025 21:57:23 +0100 From: Christian Brauner To: Oleg Nesterov Cc: Al Viro , Kees Cook , jack@suse.cz, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, syzkaller-bugs@googlegroups.com, syzbot Subject: Re: [syzbot] [fs?] [mm?] KCSAN: data-race in bprm_execve / copy_fs (4) Message-ID: <20250323-haftverschonung-rochen-22c230317a23@brauner> References: <67dc67f0.050a0220.25ae54.001f.GAE@google.com> <202503201225.92C5F5FB1@keescook> <20250321-abdecken-infomaterial-2f373f8e3b3c@brauner> <20250322010008.GG2023217@ZenIV> <20250322155538.GA16736@redhat.com> <20250322185007.GI2023217@ZenIV> <20250323181419.GA14883@redhat.com> 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=utf-8 Content-Disposition: inline In-Reply-To: <20250323181419.GA14883@redhat.com> On Sun, Mar 23, 2025 at 07:14:21PM +0100, Oleg Nesterov wrote: > On 03/22, Al Viro wrote: > > > > On Sat, Mar 22, 2025 at 04:55:39PM +0100, Oleg Nesterov wrote: > > > > > And this means that we just need to ensure that ->in_exec is cleared > > > before this mutex is dropped, no? Something like below? > > > > Probably should work, but I wonder if it would be cleaner to have > > ->in_exec replaced with pointer to task_struct responsible. Not > > "somebody with that fs_struct for ->fs is trying to do execve(), > > has verified that nothing outside of their threads is using this > > and had been holding ->signal->cred_guard_mutex ever since then", > > but "this is the thread that..." > > perhaps... or something else to make this "not immediately obvious" > fs->in_exec more clear. Well, it would certainly help to document that cred_guard_mutex serializes concurrent exec. This is kind of important information given that begin_new_exec() and finalize_exec() are only called from ->load_binary() and are thus always located in the individual binfmt_*.c files. That makes this pretty implicit information. Let alone that the unlocking is all based on bprm->cred being set or unset. Otherwise the patch looks good to me. > > But I guess we need something simple for -stable, so will you agree > with this fix for now? Apart from changelog/comments. > > retval = de_thread(me); > + current->fs->in_exec = 0; > if (retval) > current->fs->in_exec = 0; > > is correct but looks confusing. See "V2" below, it clears fs->in_exec > after the "if (retval)" check. > > syzbot says: > > Unfortunately, I don't have any reproducer for this issue yet. > > so I guess "#syz test: " is pointless right now... > > Oleg. > --- > > diff --git a/fs/exec.c b/fs/exec.c > index 506cd411f4ac..02e8824fc9cd 100644 > --- a/fs/exec.c > +++ b/fs/exec.c > @@ -1236,6 +1236,7 @@ int begin_new_exec(struct linux_binprm * bprm) > if (retval) > goto out; > > + current->fs->in_exec = 0; > /* > * Cancel any io_uring activity across execve > */ > @@ -1497,6 +1498,8 @@ static void free_bprm(struct linux_binprm *bprm) > } > free_arg_pages(bprm); > if (bprm->cred) { > + // for the case exec fails before de_thread() > + current->fs->in_exec = 0; > mutex_unlock(¤t->signal->cred_guard_mutex); > abort_creds(bprm->cred); > } > @@ -1862,7 +1865,6 @@ static int bprm_execve(struct linux_binprm *bprm) > > sched_mm_cid_after_execve(current); > /* execve succeeded */ > - current->fs->in_exec = 0; > current->in_execve = 0; > rseq_execve(current); > user_events_execve(current); > @@ -1881,7 +1883,6 @@ static int bprm_execve(struct linux_binprm *bprm) > force_fatal_sig(SIGSEGV); > > sched_mm_cid_after_execve(current); > - current->fs->in_exec = 0; > current->in_execve = 0; > > return retval; >